L-i2lL
                                   c-a
//
—
    jffliilllilliiiliriiir
                                                                       f

           *<•>''•&;
                a- -.-.. - -,•%-;. y|(s-' -wt™^.'
                                          i(.-.-«.!...,g».VJ


                                                                                          Say

-------
                PUBLISHED BY
 THE MARYLAND DEPARTMENT OF NATURAL RESOURCES
           TIDEWATER ADMINISTRATION
CHESAPEAKE BAY  RESEARCH AND MONITORING DIVISION
                    FOR
         THE CHESAPEAKE BAY PROGRAM

-------
  Chesapeake Bay Strategy
           for the
 Restoration and Protection
              of
Ecologically Valuable Species
          Prepared by

of
        September
        CBP/TRS 115/94

-------

-------
                             ADOPTION
      We, the undersigned, adopt the Chesapeake Bay Strategy for the Restoration and
Protection of Ecologically Valuable Species, in fulfillment of the commitments of the Living
Resources section of the 1987 Chesapeake Bay Agreement:

       "to develop, adopt, and begin to implement a Bay-wide plan for ... ecologically
      valuable species," and  "the development of Bay-wide  resource management
      strategies for... ecologically valuable species. *

      We agree  to  accept the Strategy as a  guide  in  the restoration  and protection of
ecologically valuable species and their functional roles in the Chesapeake ecosystem.  We agree
to support this Strategy as a mechanism for cross-program integration of the various fishery
management plans, waterfowl management plans, habitat restoration plans, and other Chesapeake
Bay  Program  plans.    We further  agree to  work  together to  implement the  major
recommendations of the Strategy:  (1) provision of educational and informational aids to
understanding the Bay as an  ecosystem, (2) pursuit of a  program to develop simulation models
of the Chesapeake ecosystem,  (3) development of a comprehensive  habitat restoration and
management plan for Chesapeake Bay, (4) development and implementation of a  consistent
system of biological indicators of ecosystem integrity, (5) continuing long-term support for key
living resources monitoring  programs, (6) expand the  utility of the  Chesapeake Bay  living
resources database as outlined in the Strategy, and (7) promote directed research on ecologically
valuable species.

      We          the      to         long-term,   stable          support and human
resources to the               the indigenous        habitats and          diversity of the
Chesapeake region.


For the                  of Virginia

For the State of Maryland

For the Commonwealth of Pennsylvania
For the United States of America
For the District of Columbia
For the Chesapeake Bay Commission
^^A^^^X^
'^^TM^L
                                                                                      ill

-------
                        ACKHOWLEDGEHEPfTS

     We want to thank all the members of the Ecologically Valuable Species
     Workgroup for their valuable input. This work could not have been
     completed without the help of a grant from the Maryland Coastal
     Management Program and staff support of the Maryland Department of
     Natural Resources. We also want to thank the members of the Living
     Resources and Monitoring Subcommittees, and the  contributing
     authors (see Appendix B).
     Partial funding support provided by the Coastal Zone Management
     Program of the Maryland Department of Natural Resources, pursuant
     to the National Oceanic and Atmospheric Administration Award No.
     NA27OZO357-O1.
iv

-------
                                                             SUMMARY
Overview
In 1987, executives of the Chesapeake Bay Commission, the District of Columbia, Maryland, Pennsylvania, Virginia and the U.S.
Environmental  Protection  Agency  signed the  Chesapeake  Bay Agreement,  pledging  to initiate management  plans  for
"commercially, recreationally, and ecologically valuable species." To meet the  last  part of this commitment, the Ecologically
Valuable Species Workgroup was organized by the Living Resources Subcommittee of the Chesapeake Bay Program, and charged
with development of a plan for ecologically valuable species. The concept developed by the Work Group, in consultation with
a group of scientific experts, is not a management plan in the traditional sense, but rather a strategic plan: to view the Bay as
an ecosystem, composed of biological communities that interact with  the physical  and chemical factors of their surroundings
to function as a single unit; and to build management recommendations around this holistic view of the Chesapeake ecosystem.
The ecologically valuable species in the Bay connect management in all  domains (e.g., fisheries, water quality,  and habitat) to
ecosystem responses, but usually cannot be managed directly. Therefore, this Strategy  has provided  an opportunity to explore
and make more explicit the connections within the spectrum of management efforts to restore and protect the Chesapeake.
The better-known Chesapeake Bay species, the oysters, crabs,
striped bass,  and wildlife, depend on ecologically valuable
species  for  survival: for  nutrients  and  energy,  habitat
structure, and relief from predators and competitors. Many
ecologically  valuable species,  though  most people would
recognize  neither their names  or appearances,  are the
balancing  elements in the Bay ecosystem. No matter what
is  done to control nutrients  and improve habitat condi-
tions, there  must be an adequate  base  of zooplankton,
forage fish and benthic  animals for healthy and productive
populations of recreational  and commercial finfish to be
supported.

Ecologically valuable species are defined in the Strategy as
those species  or groups of species that have significant
functions  in  the ecosystem, by:

   1)   regulating populations of other species (prey and
        predators);
   2)   regulating the  quantity and quality of habitat for
        other species (e.g., oysters and submersed aquatic
        vegetation);
   3)   processing  large  amounts of material (nutrients,
        organic and inorganic matter) by both  physical
        and  chemical  means  (phytoplankton,   bacteria,
        filter feeders); or
   4)   producing  organic matter  (phytoplankton,  SAV,
        plants of marshes and shorelines).
This definition does not exclude species of commercial and
recreational importance, but rather puts them in context as
members of biological communities where they are valuable
for their ecological  functions rather than for their value to
humans.

Vision of the Chesapeake ecosystem
The vision of the Chesapeake Bay ecosystem developed in
the Strategy derives  directly from the 1987 Bay Agreement.
The framers  of the Agreement  realized that "...the entire
system must be balanced, healthy, and productive."  The
Strategy offers working definitions of "balanced," "healthy,"
and "productive,"  and explores  the implications  of this
vision for management, monitoring, and research.

        Balanced
        having sufficient  populations  of prey  species to
        support the species at the  top of the food chain,
        and to limit overabundance at the bottom of the
        food chain; no major function of the ecosystem
        dominates the others;

        Healthy
        having diverse populations that fluctuate within
        acceptable  bounds; free from  serious impacts of
        toxic  contaminants,  parasites,  and  pathogens;
        having sufficient habitat to support a diversity of
        species;

-------
        Productive
        providing  sufficient production  of  harvestable
        products to serve human needs without depleting
        predator  and  grazer populations  to the  point
        where internal, functional balance is disrupted.

Management
Because most of the ecologically valuable species cannot be
managed directly, the Work Group had to ask "what are the
control points where management can help to achieve the
vision  of a  balanced, healthy and productive ecosystem?"
For  example, the concepts  of  top-down and bottom-up
ecosystem control  are  discussed  in the context  of the
Chesapeake  system. In the Chesapeake, bottom-up control
is represented principally by nutrient management, a central
focus of the Bay  Program since its inception. Top-down
control includes protection  and restoration of fisheries
populations  and their  habitats, a more recent and less
certain  aspect  of Bay  management.  The  interaction  of
bottom-up  and top-down  controls  needed  to  attain  a
balanced and productive  ecosystem  is not known for the
Chesapeake. The Strategy recommends filling this knowledge
gap by developing simulation models of the ecosystem, so
that the results of various mixes  of controls  can be predict-
ed.

The Strategy also recommends the development of educa-
tional  materials to better inform both managers  and the
public about ecologically valuable species and  their vital
roles in the  ecosytem.

Monitoring
Effective management depends on up-to-date feedback from
the ecosystem.  Traditionally, the Chesapeake Bay Program
has relied largely on  measures of water quality (dissolved
oxygen, nutrients, and  chlorophyll), supplemented by the
status  of a  few major  fishery  resources, to  measure the
integrity of the Chesapeake ecosystem. Ecosystem indicators
(including both biological and  habitat indicators) can be
more directly reflective  of balance, health and productivity
than  chemical or  physical  monitoring,  and  are  readily
available  or can be  developed with  relative  ease.  These
community-based  indicators  are  more reflective  of the
balance,  health, and productivity of ecologically  valuable
species than, for example, fishery statistics  or other abun-
dance  indices for commerical fishery species. The Strategy
advocates the further  development and consistent use of
ecosystem indicators.

Research
Many of the most important ecologically valuable species in
the Bay are  also some  of the least known,  in terms of life
histories, habitat requirements, and interactions with other
species. These species  seldom receive priority in  research
programs, although recent studies  of small reef fishes,
gelatinous predators (sea nettles and comb jellies), zooplank-
ton, and planktonic bacteria have added greatly to  our
understanding of some important ecosystem processes. The
Strategy recommmends the development of a research plan
for ecologically valuable species to  help  fill  the many
remaining gaps in our knowledge of these species and their
functions.

Specific recommendations
The principal recommendations  of the Strategy are summa-
rized  below.

•        Apply available  information on  species  interac-
         tions and habitat requirements in the development
         and revision of fishery  management plans.

•        Incorporate habitat goals for living resources into
         tributary-specific nutrient reduction strategies.

*        Provide  information to management and to the
         public to support and reinforce recognition of the
         importance of ecologically valuable species.

8        Publish  and  continually update  a  handbook of
         ecosystem indicators for  Chesapeake  Bay. This
         handbook will  include  information on  measure-
         ments and their interpretation.

•        Use information  gathered directly from the  Bay
         ecosystem for effective management. This approach
         will require continued  monitoring of ecologically
         valuable species, and the development of a consis-
         tent program  for ecosystem indicators of biological
         integrity.

«        Coordinate   ecosystem  modeling  efforts,  and
         update models used by management with state-of-
         the-art  ecological knowledge.  Computer simula-
 VI

-------
tions  of the ecosystem have  demonstrated  their
effectiveness in the diagnosis of prevailing condi-
tions. Simulation will be  useful to Bay managers
for prediction  of future  outcomes  given  certain
changes in nutrient and toxic levels, area available
for habitat, and other factors  important to living
resources.

Develop a comprehensive habitat  restoration and
management plan to achieve the goals of the 1987
Bay Agreement and the 1992 Amendments which
would benefit the maximum number  of species:
commercial, recreational, and ecologically valuable
ones alike.

Develop a list of priority research topics directed
at ecologically valuable species and communities.
This will  notify research institutions of particular
needs, and should stimulate researchers to explore
these subjects.
                        *-& fl.
                         tgiMP^i
                                                                                                            Vfl

-------

-------
                                            CONTENTS
Adoption Statement

Acknowledgments

Executive Summary

Introduction

       Vision — toward a balanced ecosystem

       Status of ecosystem indicators

       Management recommendations and tools

       Implementation Matrix

       References

Appendix A: List of Species

Appendix B:

       Microbial Loop

       Phytoplankton
           Maryland perspective:
           Virginia perspective:

       Zooplankton

       Forage Fishes

       Benthos

       Oyster Reefs

       Crustaceans

       Waterbirds
       Submersed Aquatic
       Vegetation
                                                  ui
Jon H. Tuttle


Kevin Sellner
Harold G. Marshall

Ray S. Birdsong and Claire Buchanan

E.D. Houde

Daniel M. Dauer, J. Gerritsen and J.A. Ranasinghe

Roger I.E. Newell and Denise Breitburg

John R. McConaugha and Steve Rebach

Dennis G. Jorde, G. Michael Haramis
and Douglas J. Forsell

Robert J.  Orth and  William, C. Dennison
 I

 4

 6

11

16

18

21

25

27


35
41

45

51

55

61

65


69

77
       Wetlands
J. Court Stevenson and Edward Pendleton
83

-------

-------

Background
This strategy was developed by  the  Ecologically Valuable
Species Work Group of the Chesapeake Bay Program Living
Resources Subcommittee to fulfill one of the commitments
of the Living Resources section of the 1987 Chesapeake Bay
Agreement:  "to develop,  adopt,  and begin  to  implement
Bay-wide management plans .  . . for ecologically valuable
species." The work group developed the concept that the
best approach to a strategy for ecologically valuable species
would be one which viewed  the Bay as an ecosystem  com-
prised of communities, structural  groups of species, abiotic
(physical and  chemical)  factors,  and their interactions.
Besides  affording a feasible method for developing the
strategy, the ecosystem  concept provides the basis for explor-
ing the  relationships between the many separate plans for
management of Chesapeake Bay species, habitats, and water
quality.  The preamble of the Bay Agreement commits the
signatories  to  "managing the Bay as an integrated  ecosys-
tem"; in the Living Resources section of the Agreement, the
signatories  agreed that "the  entire system must be healthy
and productive." A  balanced,  healthy,  and  productive
ecosystem depends upon the integrity of communities of
ecologically valuable species  and the maintenance of their
functional roles.
peake Bay restoration. Several of the most important habitat
issues for Bay species have been addressed by specific plans,
e.g., the  Wetlands Policy and Implementation  Plan (CEC
1988a; PSC 1990), the Submerged Aquatic Vegetation Policy
and Implementation Plan (CEC 1989; CEC 1990), and the
Strategy  for  Removing Barriers  to  Fish Migration (CEC
1988c).  Therefore,  habitat-based   plans  for   individual
ecologically valuable species would, to a large extent,  be
redundant with  existing plans.  A  need  was  recognized,
however, to coordinate various  habitat management plans
and initiatives within  a common framework. A long-term
commitment  to  the goals  of the  1987  Chesapeake Bay
Agreement will require long-term monitoring, the use of
ecosystem indicators, data management and  analysis, eco-
system  simulation  and  analysis,  research  and  habitat
management.

Selected ecologically valuable species and species groups are
shown in Table  1. It is  possible to describe  the roles of
these species  groups in the larger  ecosystem,  to  estimate
their status with respect to  baseline  conditions,  and  to
define some  of the stresses  which may have compromised
biotic communities and their functions.
In considering the possibilities for management plans for
ecologically valuable species,  it became clear  that, in the
traditional sense, there were few, if any, realistic options for
"managing"  many  critically  important Chesapeake Bay
species such  as the bay anchovy,  hogchoker, sea nettle,  or
numerous species of planktonic and benthic organisms. For
the majority  of ecologically valuable species the focus must
be on the environmental conditions and habitats necessary
to support their populations and maintain their functional
roles, rather than the usual focus of management plans for
fish and  shellfish, i.e. regulating harvests.

There are a variety of habitat issues  for these  species, and
the work group  considered the idea of recommending a
series of management plans  based  upon  restoring and
protecting habitats. Various  attempts to  describe  critical
habitats are well intended efforts to direct limited resources.
However, the implication that there  are less critical or non-
essential  habitats is counter to the primary goal of restoring
a balanced ecosystem. The habitats and habitat problems of
ecologically valuable species are shared with  many other,
often commercially  valuable species.  For example,  the
distribution  of bay anchovy is thought to be  restricted  by
low dissolved oxygen in deeper waters of the  Bay (Houde
and Zastrow 1991), but this problem exists for many other
species as well, and already is  a central focus of the Chesa-
Goal
The primary goal of this strategy is identical to a principal
goal of the Chesapeake Bay Agreement:

«   to restore a more balanced ecosystem  in Chesapeake Bay.

The strategy  proposes  that this goal  demands  special
attention  to ecologically  valuable  species, coupled  with
actions directed toward achieving "a  more balanced ecosys-
tem,"  measuring its properties, and predicting results of
management actions on the  ecosystem and its  constituent
communities.
Objectives
•   to focus management and research attention on the importance
    of non-harvested species and functional groups of species;

*   to protect and restore the functions of subsystems of the Bay
    ecosystem, e.g., reef communities, pelagic, soft bottom, areas of
    submerged  aquatic  vegetation (SAV beds), and  wetlands
    communities;

"   to find common ground,  in an  ecosystem context, for  the
    development and implementation of species-specific and habitat
    management plans, and to foster an overall, ecosystem- and
    community-oriented view of management activities;

-------
Table 1. Ecologically valuable species occur within communities.
These communities are often subdivided based on the functional
roles of species, their habitat preferences, or sampling consider-
ations.  Examples are:  chemical activity (bacteria); size fractions
(plankton); feeding method or diet (macrofauna);  or growth habit
(vegetation). In general, moderate abundances of many diverse
species indicate a healthy ecosystem.
  Community           Category

  Bacteria               heterotrophic aerobic group
                        sulfate reduction community

  Phytoplankton          <3 urn
                        3-10 urn
                        >10 urn

  Zooplankton            44-202 urn
                        202-505 um
                        >505 um

  Benthic Infauna         obligate  suspension feeders
                        facultative suspension feeders
                        surface deposit feeders
                        subsurface deposit feeders
                        predators

  Benthic Epifauna       filter feeders
                        opportunistic omnivores
                        parasites

  Fish                   planktivores
                        benthivores
                        carnivores

  Waterbirds             planktivores
                        herbivores
                        omnivores
                        predators

  Vegetation             submerged aquatic vegetation (SAV)
                        emergent vegetation
fish, including bay  anchovy, silversides and other species,
may exert  significant control over the abundance of both
their prey  (largely consisting  of crustacean zooplankton)
and their predators  (especially larger fish like striped bass);

2) regulating the quantity and quality of physical habitat for
other species; these roles are fulfilled by submerged vascular
plants,  marsh  grasses,  burrowing animals  and numerous
species  of hard-shelled molluscs and  crustaceans;

3) physical and chemical processing  of large amounts  of
material (nutrients, organic and inorganic matter); the form
and distribution of large  quantities of these materials are
controlled  by complex communities of benthic  and plank-
tonic organisms;
4) producing organic matter; phytoplankton,  macroalgae,
and vascular plants provide the living and detrital  matter
upon which  the Bay's food chains depend.

Ecological  importance  of a  species  does  not  preclude
economic importance and vice versa.  For example,  spot
(Leiostomus xanthurus) are important in  commercial and
recreational fisheries,  but  also are important regulators of
benthic  communities  through  heavy  predation  on  the
benthic fauna  (Homer and  Mihursky  1991). Oysters and
blue crabs  are  species of prime economic  importance, but
also have tremendous ecological importance because of their
functional  roles as consumers, recyclers, prey,  and  (in the
case of oysters) as physical habitat for many other species.
This strategy does not exclude these species because of their
commercial and  recreational  importance,  but rather puts
them in context as members of ecological communities and
functional  groups.
"   to propose measures of ecosystem and community integrity that
    will be practical, responsive, and informative to management
    programs;

*   to guide the improvement and use of analysis tools, including
    ecosystem simulation.

Definitions
Ecologically valuable species
Ecologically valuable species are defined as those species or
groups of species which  have significant functions in the
ecosystem by.

1)  regulating populations  of other species;  for  example:
gelatinous zooplankton may exert significant control over
their prey, primarily  crustacean  zooplankton; also forage
Ecosystem
The Chesapeake Bay ecosystem is defined for the purposes
of  this strategy as the tidal waters  and tidal wetlands of
Chesapeake Bay, along with adjacent upland margins, and
includes the physical and chemical environment, the biota,
and the watershed inputs  to the  tidal  system.  Non-tidal
waters, wetlands, and uplands of the Chesapeake watershed
are excluded from this definition in order to set reasonable
boundaries  and to  avoid an unworkable  degree of com-
plexity, although  it is recognized that substantial  energy
flows and other effects originate from  these sources.

Structure of the Strategy
In  the  following  sections,  we present  1)  a vision of a
balanced,  healthy, and productive  ecosystem;  2)  an  as-
sessment  of  the  current  status  of  available  ecosystem

-------
indicators with  respect to the baseline  vision; 3) general
recommendations and a proposed  set of tools for accom-
plishing the goals of the strategy; and 4) specific recommen-
dations for implementation of the strategy.

-------
                       VISION - TOWARD  A BALANCED  ECOSYSTEM
What is  a  "balanced, healthy, and  productive" ecosystem?
Because there is not, as yet, a complete quantitative under-
standing of this idea, qualitative and aesthetic views prevail,
A Bay teeming with game fish, blue crabs, oysters, and wa-
terfowl, with clear, water and  a  minimum of "nuisance"
organisms  (algae, sea nettles, bacteria, too-dense SAV beds)
is a pleasant, if perhaps unrealistic vision  (each of these
"nuisance groups" has a vital role to play in a balanced and
healthy system).

There is a tendency to think of natural systems as unchang-
ing or static, but in reality they are dynamic, governed  by
internal  processes,  stressed  by external  forces,  and char-
acterized more  by change than by stasis. The terms "stable"
and "stability" as applied to ecological systems do not mean
that they are permanently invariable, but rather that they
exhibit dynamic equilibrium  over relatively long periods of
time; permanent changes in function and the structure of
populations and communities take  place slowly over time,
not suddenly. Populations in stable systems may fluctuate
dramatically  in abundance  over seasons or decades, but
nevertheless  maintain  constant  baselines, or  long term
average abundances. All ecosystems  change drastically over
climatic,  evolutionary, and geologic time scales.

Ecological balance may best be defined in functional terms,
i.e.,  as  a  balance between  producers, consumers,  and
detritivores such that material (e.g.,  organic carbon) is pro-
duced in rough proportion to consumption, and does not
accumulate  or  dissipate in  excessive  amounts. Balanced
ecosystems tend to  remain relatively stable in productivity,
species diversity, and population structure over long periods
of time.

The problem of eutrophication in Chesapeake Bay appears
to be reflected in an imbalance between primary producers
(phytoplankton) and higher order consumers (e.g., fish). The
consumption  of excess  production  by bacteria depletes
dissolved oxygen, and makes portions of the Bay unsuitable
habitat for higher order consumers,  while bacteria continue
to thrive. The system has been shifted "out of balance"  by
the introduction of excess  nutrients  and  waste  products
from human activities. In addition, fisheries have contribut-
ed  to  the depletion  of populations  of some  consumer
organisms  (e.g., oysters), probably further shifting the bal-
ance towards algae (producers) and detritivores, especially
bacteria.

' Health" is a very loose term to  apply to an ecosystem; it
would be awkward to describe an "unhealthy" or "sick"
ecosystem. More accurate  terms are  stress (a response  to
stressors, e.g., nutrients, toxic contaminants, pathogens) and
disturbance (e.g., destruction of wetlands and other habitats).
Stressed and disturbed ecosystems may show imbalances or
departures  from stable  conditions,  as  well as  reduced
productivity of some  or all components. Stress and distur-
bance also can favor the proliferation of tolerant, opportu-
nistic ("weedy"), and exotic species, some of which are
nuisances to human activities or outcompete more desirable
species.

Productivity is an important element to  consider in devel-
oping this  vision of the  ecosystem. The Bay is, by  most
accounts, too  productive  of phytoplankton  and  bacteria
because of an overabundance of nutrients. But what is a
suitable level of productivity? Could the  Bay be engineered
so as to convert existing nutrient loads into biomass useful
to humans (fish, shellfish, and  other wildlife) instead of
bacteria  and biochemical oxygen demand? It is  plausible
that  the  Bay could be managed to produce  much greater
quantities of edible fish  and shellfish than under pristine
conditions. Would  this scenario be  compatible  with our
qualitative and aesthetic vision? Do we want a wild Bay or
a cultivated one? Overly stringent nutrient reductions, with-
out compensatory changes in the way we use and manage
the Bay's resources, might lead to a system less productive
of harvestable  resources than we would wish.

The  Chesapeake Bay Program  has  used  a "bottom-up"
approach in its attempt to restore the biological integrity of
the Bay,  i.e., a 40%  reduction in nutrient input, along with
habitat  protection  and  restoration.  But the "top-down"
approach also needs to be considered. A top-down strategy
recognizes that sizeable populations of top predators such
as striped bass, bluefish, and predatory birds are as necessary
to a balanced ecosystem as is nutrient reduction. Removing
top predators by heavy harvesting can increase the size and
abundance of their prey (forage fish), which in turn puts se-
vere predation  pressure  on  the primary consumers  (zoo-
plankton),  and  thereby  lessens grazing pressure  on the
phytoplankton.  Depletion of benthic filter-feeding organ-
isms  (oysters,  clams, and  many  species that  primarily
inhabit  oyster  shells) through harvest, disease,  loss of
habitat,  and low dissolved oxygen  also acts to favor an
overabundance  of phytoplankton.  The filter-feeders  are
equivalent in importance to zooplankton as consumers of
phytoplankton  in  shallow  reaches  of  the  Bay and its
tributaries.

Phytoplankton  are the  main source  of organic  matter in
large areas of the Bay; if they are not consumed (mostly by
zooplankton and other filter feeders), they die and  either
are consumed by bacteria, or accumulate  in bottom sedi-
ments, where they may be buried or consumed by bacteria

-------
at a later season. Bacterial respiration (biological burning of
organic fuel) is the major cause of dissolved oxygen deple-
tion in the Bay. Recent modeling exercises indicate  that
bacterioplankton oxygen consumption is most important in
the spring, whereas sediment sulfide production and subse-
quent sulfide  oxidation (a bacterial and  chemical process
that depletes dissolved  oxygen)  becomes dominant during
the summer.  Nutrient  management  (bottom-up control)
seeks to alleviate the problems of low dissolved oxygen and
excessive turbidity  by limiting  the production  of phyto-
plankton. Strategies to increase grazing by larger, longer-
lived organisms (top-down control) could help to achieve
these ends while allowing higher overall productivity, by
channeling primary productivity to fish and shellfish rather
than to oxygen-consuming bacteria. A combination of top-
down and bottom-up  approaches probably needs  to be
employed to restore the biological integrity of  the Bay.

Whether one takes a top-down or bottom-up perspective on
the Bay restoration, it is largely the species in the middle
(primary and  intermediate  consumers) that link manage-
ment actions  to  the intended results.  No  matter what is
done to control nutrients and improve habitat conditions,
there must be an adequate base of zooplankton, forage fish
and  macrobenthos to  support healthy and  productive
populations of recreational  and commercial finfish. Many
ecologically valuable species, although most people would
recognize neither their names nor their appearances, are the
"species in the middle" - balancing elements in  the Bay eco-
system.

Our .vision therefore can be summarized as a  Chesapeake
Bay ecosystem which is:
Balanced
having sufficient populations of prey species to support the
species at the top of the food chain, and to limit overabun-
dance at the bottom of the food chain; no major function
of the ecosystem dominates the others;
Healthy
having diverse populations that fluctuate within acceptable
bounds;  free from  serious impacts of toxic contaminants,
parasites, and   pathogens;  having  sufficient habitat  to
support a diversity  of species;
Productive
providing sufficient production of harvestable products to
serve human needs without depleting predator and grazer
populations to the point where internal, functional balance
is disrupted.
This vision implies that human uses should be planned so
as to balance inputs of nutrients and organic matter (wastes)
with removal (harvests), while taking into account internal
sources (carbon and nitrogen fixation) and sinks (burial and
denitrification).  Management  actions  should be taken to
reduce stress factors  (contaminants,  diseases)  and  distur-
bance (habitat destruction and alteration,  introduction of
exotic species) wherever possible. Specific recommendations
relating to these and  other  issues for ecologically valuable
species are contained in the MANAGEMENT RECOMMENDATIONS
AND TOOLS section.

-------
                                           OF                      INDICATORS
General considerations
How can the integrity of the Chesapeake ecosystem best be
measured? To date, the Bay Program has relied largely on
measures of water quality (e.g., dissolved oxygen, nutrients,
and chlorophyll) supplemented by the status of a few major
fishery  resources,  to  assess  the "State of the Bay." Other
indicators,  including  biological community and  habitat
measures,  with  broader ecological  relevance, are readily
available or could be developed with relative ease.

The use of ecosystem  indicators in management programs
is entirely dependent on monitoring programs to generate
the necessary data on biological communities and their hab-
itats. Biological  monitoring can be more directly reflective
of balance,  health  and  productivity  than  chemical or
physical monitoring.

Several  existing  or planned monitoring programs provide
information on  biological communities and habitat condi-
tions  for  the Bay's living resources. The Bay-wide  water
quality  monitoring program includes  extensive measure-
ments of important habitat  variables, including dissolved
oxygen, nutrients,  light attenuation, and  total suspended
solids. Biological communities - phytoplankton, zooplank-
ton, and benthic infauna - are monitored as a part of this
program. In addition to the presence or absence of specific
organisms, the diversity of species and habitat are important
indicators.  Many  ecologically valuable  species of fish are
monitored as by-catch in surveys directed at commercial spe-
cies. Although sampling methods may not be ideal  for most
non-commercial species, valuable data are obtained at little
extra cost. Areas of submerged  aquatic vegetation  beds are
measured regularly, using both aerial and ground surveying
techniques. Oyster reefs are monitored by fisheries manage-
ment agencies  in  Maryland and  Virginia,  not  just for
oysters,  but also for selected predators  and fouling organ-
isms that share this habitat. Wetland monitoring is part of
the Chesapeake  Bay Wetlands Policy Implementation Plan.
A workshop was held in April  1992 to develop consensus
on a wetlands monitoring program.

Below,  we list  general  criteria for  ecosystem indicators,
describe indicators  that  can be generated  from  existing
monitoring programs, their  recent status,  if available, and
recommend additional steps for their development and use.
Single-species indicators (e.g., juvenile fish indices, harvest
statistics) often  have large sources  of variation and  biases
that  cause  difficulty in relating them to the  health of the
ecosystem. Mobile or migratory species can be components
of indicators if acute changes occur while the population
resides  in the region of interest, as for  example fish kills,
blocks  to  migration  due to  low  oxygen, avian  cholera,
eggshell thinning, etc.  Biological measures may be used as
indicators of ecosystem status and integrity if they possess
the following attributes:

«   indicator increases or decreases can be tied to issues of
    management concern;

«   temporal and spatial variabilities  in the measures can be
    reasonably well documented, predicted, and understood;

«   variance in statistically valid indices is not so great so as
    to preclude practical  and affordable sampling;

H   indicator changes due to management can be separated
    from changes due to natural environmental factors caus-
    ing variability,

«   indicator responses are rapid enough to be detectable;

«   indicators are not  overly sensitive to effects  outside the
    region of interest.

Indicators usually are  most  informative and  robust if they
integrate important  attributes of the structures and func-
tions of biological communities.

Description and status of ecosystem indicators
A  synopsis  of ecologically  valuable groups and habitat
considerations is  given below. All major groups have been
included,  even though,  for  practical  reasons,  some  have
little potential as  indicators. Table 2 presents an overview of
potentially useful indicators.

Submerged aquatic vegetation
The distribution and  coverage of  submerged  aquatic
vegetation  (SAV)  are  recognized as  important  ecosystem
indicators,  and the relationship of SAV status to nutrients,
chlorophyll, and  turbidity are fairly well understood (Den-
nison et al.  1993). Also,  SAV beds are understood to have
important functions as 1) physical and biological filters that
remove nutrients and suspended sediments from the water;
2) as physical habitat and centers  of abundance for fish,
crabs, and other invertebrates;  3)  as  important  primary
producers;  and 4) as food for waterfowl (Hurley 1991).

Bay-wide monitoring  of  SAV has been conducted almost
annually since  1984.  The  Baywide acreage of  SAV  has
become an accepted statistic for assessing the health of the
Bay, and for following trends in the improvement of water
quality. The  geographical  distribution  of  SAV also  is
important; for example,  the reappearance of SAV in the
upper tidal Potomac River has been correlated with regional

-------
Table 2. Description, status, and trends of ecosystem indicators. Specific references should be consulted for more complete information.
     HABITAT
     INDICATORS
USES
                                                    STATUS
                                                                      TRENDS
     Seagrass beds    fish spawning, crab nursery, waterfowl food source
     Water quality

     Reefs

     Wetlands/
     shorelines
     BIOLOGICAL
     INDICATORS

     Seagrasses
     Phytoplankton
     Zooplankton

     Benthos
         Infauna
         Epifauna

     Fish
     Bacteria
                                                    variable by region   improving
all ecologically valuable species except birds             variable           improving in some aspects

oysters, other benthic epifauna species, microorganisms    generally poor      declining

many species                                        generally fair       declining
CONSUMERS
waterfowl, snails, turtles
zooplankton, benthic species
(especially oysters and clams)

forage fish, benthic species including oysters
benthic-feeding fish (e.g. flounder), humans
benthic-feeding fish (e.g. drum), humans

other fish, birds, marine mammals, humans
microzooplankton
                                                                           INDICATIONS
water clarity, suspended particles, chlorophyll a,
dissolved inorganic nitrogen and phosphorus

water quality, quality of food for consumers,
short term changes

water quality, quality and quantity of food for
consumers, short term changes

environmental impacts, water and sediment quality
not established; data available

trends in seasonal distribution, health
and balance of tributaries

biological oxygen demand,
carbon and nutrient  cycling
improvements in water quality and fisheries  (Carter et al.
1988; Fewlass 1991). Management has made extensive efforts
to set targets for SAV restoration in all dimensions: distribu-
tion, density and species diversity.

Because  SAV so  well  integrates  ecological function  with
water quality, it  is recommended that  annual monitoring
continue,  and  that  annual  acreage  statistics  should  be
generated for all major segments of the Bay and Baywide.
Because  SAV abundance and distribution  can  fluctuate
considerably from year to year in  response  to hydrologic
conditions, it is suggested that multi-year running means of
acreage would be more indicative  of trends than year-to-year
changes. The possibility of predictive relationships between
SAV occurrence and abundance, and recruitment of juvenile
fish, crabs, and molluscs should be explored.

Phytoplankton
Chesapeake Bay  is presently a plankton-dominated  system
(Baird and Ulanowicz 1989). Phytoplankton are microscopic
                                           plants found throughout aquatic systems and form the base
                                           of the food web. Phytoplankton abundances, growth rates,
                                           and  species  composition respond directly to changes in
                                           nutrient  concentrations,  turbidity,  and   contaminants.
                                           Phytoplankton  production, accumulation and subsequent
                                           decomposition  translate into changes  in the quality  and
                                           quantity of food  available at the  base of the food chain,
                                           thereby affecting the livelihood of many consumer species
                                           as well as  nutrients and dissolved oxygen. Phytoplankton
                                           assemblages (abundance and species composition) have been
                                           monitored on a Bay-wide basis for several years, but there
                                           has been insufficient effort to interpret these data in an eco-
                                           system context. Given appropriate analytical attention, these
                                           groups have  considerable promise for 1) reflecting changes
                                           in the system over fairly short time spans, because most
                                           generation times are short; and 2) providing information on
                                           functional aspects of  the system  that are  important to
                                           higher trophic levels.

                                           Indices of species composition, ratios of green to blue-green
                                           algal  cells  or diatoms  to  dinoflagellates, size spectra,  and

-------
diversity indices are potential  indicators  both of  water
quality and of the quality of food for higher organisms. For
example, diatoms are considered to be more suitable food
for oysters  and  other  bivalves than  blue-green  algae  or
dinoflagellates. These community indicators have not been
widely used  or  evaluated for Chesapeake Bay until recently.
It  is  recommended that candidate indicators  should  be
calculated from the existing data to determine their vari-
ability and  potential for routine use in reporting moni-
toring data.

Zooplankton
Zooplankton are a link between water quality  and living
resources. The populations in this group respond quickly to
habitat  conditions  and, therefore,  are good indicators  of
both short-term and long-term shifts in the Chesapeake Bay
environment. They are critical connectors between primary
producers (phytoplankton) and higher consumers, providing
the bulk of the forage prey for most larval and juvenile fish-
es. In addition, many other estuarine organisms and  adult
fish of species such as anchovies or silversides  rely on them
for prey. They have a key role in models being developed to
track the  movement of toxic  compounds through food
chain pathways.

Zooplankton have  been monitored  Bay-wide  for several
years, and, with an accumulation of 5-7 years of data,  are
beginning  to  show  significant   trends.  Unfortunately,
budgetary problems have forced reductions in monitoring
effort, and  threatened  the overall  program. This is  an
example of ecologically valuable species "falling through  the
cracks"  of management and monitoring programs  because
they are not perceived  to  have direct  relevance either  to
water quality or to commercial and recreational species. The
great  importance of the Zooplankton  component of  the
ecosystem argues for continued monitoring and greater
efforts  to interpret existing data in  terms of ecological
function and  integrity. A  Zooplankton  monitoring work-
shop held in September 1991 addressed these questions (Bu-
chanan  1992). The focus was on use of the monitoring data
in a  more  integrated  context,  and  the development  of
indicator statistics  which would be responsive to system
integrity.

Benthos
Benthic  infaunal   assemblages  have  been   monitored
extensively in Chesapeake Bay, both as part of the Bay-wide
monitoring program and to evaluate environmental impacts
(e.g.,  of power  plant  operations  and  dredged  material
disposal sites). Therefore, there  is a large database of infor-
mation  on the abundance, distribution, species composition,
and  ei.-'ironmental  associations of benthic infauna. Esti-
mates of the macrobenthic  infaunal community  are used to
indicate environmental health because benthic  animals 1)
are relatively sedentary (cannot avoid water quality prob-
lems), 2) consist of species that exhibit different tolerances
to stress, and 3) have relatively long life spans (indicate and
integrate water quality problems over time). A significant
amount  of effort  has  been applied to interpreting the
ecological relationships of the  benthos both to water and
sediment  quality  and  to  consumer organisms.  Species
richness and overall abundance (biomass per unit area) are
used routinely  to describe these assemblages. It  is generally
recognized that with proper interpretation (e.g.,  accounting
for sediment type and salinity) these statistics are indicative
of habitat integrity and the quantity of forage available for
the many species of fish that feed on benthic fauna. More
integrative measures of benthic community integrity have
been  developed  (Luckenbach  1988; Maxted   1990) for
portions of the Bay, but have  not come  into  widespread
Benthic epifauna are largely dependent on hard surfaces for
attachment. Oyster reefs, in particular, are habitats for a
diverse assemblage of epifauna, including mussels, barnacles,
anemones, worms, small crabs, sponges and tunicates (CEC
1988b). They  are monitored as part of annual oyster sur-
veys. Up to the present, however, little use has been made
of this data.

Fish
Long term, geographically extensive  monitoring  of fish
assemblages in  the Bay and  its tributaries has provided
invaluable  data sets  for the development of  ecosystem
indicators.  Recently, these data  have been used to  identify
species which  appear to respond in  rather predictable ways
to long term  changes  in the Chesapeake ecosystem (Vaas
and Jordan 1991). The  data  also  have been  used in  the
development and calibration of  an Index of Biotic Integrity
for  tidal tributaries of Maryland.  Although this  work is
unfinished, trial IBI's have shown the capacity for discrimi-
nating both temporal  and  spatial  trends in the diversity,
abundance, and  pollution  tolerance of  these fish assem-
blages (Jordan et al. 1991). Several  non-fishery species are
fairly well-represented in these data  sets.

Birds
The Chesapeake Bay is home to  over 48 species of common
or abundant migratory waterbirds, including 26 species of
waterfowl,  two  species of  loons,  two  species of grebes,
cormorants, gannets,  six  species of gulls,  four  species  of
terns, osprey,  and bald eagles. These species are only those
which are  dependent on the  water itself (Table 3).  Many
other species of migratory birds  are dependent  on the Bay's
adjacent wetlands and shorelines.

The  geese  and  half of the ducks  are chiefly herbivores.
Other ducks  eat mollusks, insects, and  small fish.  Some
8

-------
Table 3. Number of species, season of abundance, approximate numbers, and foods of waterbirds common or abundant in the Chesapeake
Bay during at least two seasons of the year.
Birds
Loons
Grebes
Gannet
Cormorant
Herons and Egrets
Swans and Geese
Dabbling Ducks
Diving Ducks
Mergansers
Sea Ducks
Eagle and Osprey
Gulls
Terns
# of Species
2
3
1
1
5
2
6
8
2
4
2
6
4
Season
WSpF
WSpSF
WSpF
SpSF
SpSF
WSpF
WSpSF
WSpF
WSpF
WSpF
SpSF
WSpSF
SpSF
Abundance
> 16,000
> 3,000
5,000
13,000
> 25,000
>350,000
>21 0,000
>230,000
> 46,000
>260,000
> 5,000
>250,000
> 14,000
Foods
Fish
Fish, invertebrates
Fish
Fish
Fish, invertebrates
Crops, SAV
S-AV, crops, invertebrates
SAV, clams, invertebrates
Fish
Clams, invertebrates
Fish, waterfowl
Fish, invertebrates
Fish
species  which  were  largely herbivores historically  have
changed their diets with the decrease in sea  grasses. The spe-
cies which persisted in their dependence on seagrasses have
been the most  affected by the decline of SAV. It is hoped
that their populations will recover as SAV is reestablished.
Waterfowl are a symbol of the Bay region  to many people,
and a  return to former  population levels would be  wel-
comed by all.

The Bay is well known for its abundant wintering waterfowl
but less well known are the thousands of loons, grebes, and
gulls which also depend on its  rich waters  for their winter
survival. After  the  wintering   populations  depart   for
northern breeding grounds there are still large numbers of
waterfowl such as wood ducks,  black ducks, and mallards
which breed and raise their young in the Bay.

Also, many thousands of colonial waterbirds such as herons,
egrets,  cormorants, gulls  and terns  depend on the  rich
fishery and secluded nest  sites to raise their young. Other
species such as bald eagles and osprey are also ecologically
valuable.

It is difficult to assess the ecological role of such a diverse
assemblage of birds. Food habits are known for only a  few
species  and  accurate  population  figures  are difficult to
obtain due to the migratory nature of the birds and their
widespread  distributions.  Most  fish  and invertebrates
inhabiting the Bay are preyed on by some birds, but their
role in limiting prey populations, including competitors of
commercial  fish species, or controlling less fit individual
fish, is unknown.

Colonial waterbirds  may  exert  less  of  an  effect on  their
environment  than  their   environment  exerts  on  them.
However, colony sizes, numbers, and  locations  may be
worth tracking  as  rough  indicators  of environmental
quality.  Although  waders  tolerate  relatively  poor  water
quality in  terms of contaminants  (Erwin and Spendelow
1991), they  may  prove useful in  evaluating changing
contaminant loads in the Bay.

Most waterbirds of the Chesapeake Bay are migratory, thus
their populations and survival may not be  indicators of the
health of the Bay. Rather  the  populations  of waterbirds
must  be viewed  as  a  whole  because  populations  of
individual species may be limited by factors outside the Bay
region. Only with a thorough knowledge of the birds'  food
habits, life history, and  conditions in  other areas can we
understand   the  meaning  of  fluctuations  in  waterbird
populations of the Chesapeake Bay.

The baselines of waterfowl  and raptor  population indices
have  changed over  the years in relation to degradation of
the Bay. The potential for a  multi-species bird index, analo-
gous  to  indicators  of other groups,  should  be examined.
Adequate data to support such an index may already exist.

Other groups
The following groups are components of the Bay ecosystem
which have not yet been monitored sufficiently well in the
past to play the parts of ecosystem indicators.

BACTERIA
Bacteria  largely  control  cycling of  important biological
elements  including carbon,  nitrogen,  phosphorus  and
sulfur. The sheer magnitude of organic carbon  flow needed
to support the metabolism of aerobic  heterotrophic bacteria
and sulfate-reducers as well as their demonstrated role as key
players in oxygen consuming processes indicate that these
groups  should  be  targeted. Bacteria have  been  studied
                                                                                                                      9

-------
enough,  in  a research  context, to  provide  an extensive
database  which could be applied to questions of ecosystem
status for some areas of the  Bay,  but it has  not yet been
used for  this purpose.
Studies in central Chesapeake Bay have shown that bacteria
comprise a large percentage of the standing stock of carbon
during summer (Malone et al.  1986). These high bacterial
densities are associated with high water column oxygen
consumption rates. When  coupled with sediment oxygen
demand,  observed water  column  respiration  rates  are
sufficient to maintain hypoxic and anoxic conditions in the
deep areas of the central  Chesapeake during the summer
months (CEC  1988b). For example, deep water dissolved
oxygen levels in the vicinity of Cove Point, Maryland show
statistically significant decreased dissolved oxygen concentra-
tions over time (Cargo et al. 1986). Recent  evidence from
examination of mid-Bay sediments indicates increased sulfur
cycling since colonial times (Cooper and Brush 1991). There
is  growing evidence that  overenrichment by nutrients is
causing changes in the plankton which negatively affect the
supply of food to fish and shellfish.
The microbial food web (bacteria provide food  for single
celled animals, especially flagellates and possibly  ciliates) is
composed of a greater number of energy transfers than the
classic phytoplankton  -  zooplankton  - higher  animal
scheme. Thus its efficiency is lower and a smaller fraction
of production ultimately reaches  higher,   economically
important levels.
MACROALGAE
Macroalgae, generally  known as seaweed, are important
primary producers of the Bay. Some are very abundant, for
example sea lettuce (Ulva sp.), and may have significance
both as food resources and as physical habitat. Macroalgae
are important sources of nutrients  at times when  dense
windrows accumulate along shallow shorelines. Decomposi-
tion of accumulated biomass may affect dissolved oxygen
and  nutrient  concentrations significantly in some areas
(CEC 1988b).
MEIOFAUNA
Meiofauna are very small animals that inhabit  sediments
and submerged surfaces. They include nematode worms and
a variety of single-celled animals. Meiofaunal communities
have been monitored in some aquatic systems as  indicators
of pollution, but have not been monitored extensively in
Chesapeake Bay.

MOBILE EPIFAUNA
Mobile epifauna (crabs, snails, nudibranchs, reef fishes, and
other species) tend to concentrate around with oyster reefs
and  other  submerged  structures.  Because of their habitat
preferences and mobility, they often are poorly represented
in general biological  surveys.  This  makes  it difficult to
predict population trends and effectively plan for manage-
ment, even for those species which are commercially impor-
tant  such  as the blue crab. Reef fishes  can be sensitive
indicators of hypoxia  (Houde and Breitburg,  unpublished
data  1991); other members  of this group may have promise
as indicators,  but monitoring techniques have not been
fully developed.

GELATINOUS ZOOPLANKTON
All species of  gelatinous  zooplankton  are  carnivorous,
feeding on the primary consumers of the zooplankton such
as copepods and pelagic polychaetes. They also feed on  fish
eggs  and newly hatched fish larvae. In addition, sea walnuts
eat bivalve larvae, something the sea nettle is  unable to
digest. The gelatinous zooplankton themselves have very few
predators.  The  sea  nettle is  the only  significant predator
known on the sea walnut and  hydromedusae, and the sea
nettle  is  not  known  to  have any significant  predators,
although certain fish are known to prey on other species of
scyphomedusae.  Gelatinous zooplankton have an important
function as regulators of  planktomc  food chains in  the
mesohaline portion of the Bay (Baird and  Ulanowicz  1989).

Gelatinous  zooplankton  have  been  monitored  on  the
Patuxent River for many  years,  and monitored Bay-wide
from 1987 to 1990, but  budgetary reductions  have been
reflected by reductions in  the  monitoring effort.  Current
research  indicates that their overall  impact in the  Bay
mainstem on zooplankton is relatively small in comparison
to the volume of the predators.
10

-------
                    MANAGEMENT                                            TOOLS
The recommendations that follow are grouped into the fol-
lowing major categories:

* General recommendations
» Ecosystem simulation and  analysis
• Habitat Restoration and Maintenance
« Ecosystem indicators
a Monitoring
* Data management and analysis
" Research

1. General recommendations
1.1.  Develop the mechanism to make this Strategy a framework
for  coordination of the various fisheries management plans,
waterfowl management plans, habitat restoration plans, and other
Chesapeake Bay Program plans, promoting cross-program integra-
tion throughout the Chesapeake Bay Program.
With the increasing number  of Chesapeake Bay Program
management plans, there is a growing need for communica-
tion between managers and coordination  and consistency
between plans. This Strategy is laying the  groundwork for
integration of plans.

Important management  decisions  should not  be based
entirely upon considerations  of  individual system  compo-
nents  or their  interactions  in  isolation  from the larger
system  and other domains of management. For the most
part, the direction of ecosystem  responses to management
controls can be  predicted (e.g.,  nutrient reductions will
result  in less severe hypoxia,  and hence improved habitat
quality for fish, zooplankton,  and benthos), but the magni-
tudes of the  responses  are less clear, and  the ramifications
for  other structural and  functional aspects of the system
usually are  not  fully  considered.  The interrelationships
between nutrient controls,  fisheries  management,  and
restoration of habitats, for example, may be critical to the
future of the Bay. Only recently have pilot efforts been un-
dertaken  to  simulate  these  interactions; comprehensive,
quantitative predictions are not yet available. In the future,
using  the  tools  being developed now,  the Bay Program
should be able to apply a conceptual ecosystem model in all
major decision making, and to exercise caution  in imple-
menting large scale modifications that ultimately could have
unintended results.

1.1.1.  Incorporate  an  ecosystem component  into fishery man-
agement plans and programs.
The various methods of fishery management (harvest levels,
open seasons, fish passage, etc.),  will have differing effects
on the surrounding environment for other living resources.
In  the  future as more is learned, the effects  of  top-down
control and  impacts of specific fisheries on the ecosystem
as a whole will  become  clear.  Many of  the  best-known
Chesapeake Bay fishes are migratory —  having life cycles
where the young mature in one habitat,  and then migrate
seasonally to other areas as adults for spawning — effectively
transporting nutrients from one  region to another.  For
example, shad, river  herrings and striped  bass  transport
nutrients into the Bay  from both freshwater and  marine
habitats. Adult menhaden transport  nutrients out of the
Bay. Fishes  are not the  only living resources important to
nutrient cycling in  the  Bay.  Zooplankton  and  oysters
process  large amounts of suspended material, using some of
it for growth and reproduction and packaging the rest in a
form which other  organisms find  readily available. The
significant  ecological  processes  sustained by these animals
need to be considered when  managers  are  determining
priorities and making decisions.

ACTION ITEM: PURSUANT TO THE SCHEDULE OF FISHERY
MANAGEMENT PLAN RE-EVALUATIONS, REVISE OR AMEND
SELECTED FISHERY MANAGEMENT  PLANS  TO INCLUDE  ALL
AVAILABLE INFORMATION ON THE EFFECTS OF FISHERIES ON
THE ECOSYSTEM.

1.1.2. Apply living  resources  habitat goals  in  analysis and
reporting of water quality information.
As  habitat  requirements have been defined and  compiled
for many living resources (Funderburk et  al  1991, Jordan tt
al. 1992, Batiuk et al. 1992), the ability to incorporate them
into reports should be used. By  reporting not  only the
dissolved oxygen, nutrient and contaminant levels but where
the values fall in relation to the needs of living  resources
(i.e., for SAV in polyhaline waters:  DIN  <0.15, DIP <0.02)
the ecological value of changes in these levels will be made
clear. Managers will be  made aware of the  effects of their
actions  in a direct and timely way.

ACTION ITEM: BY AUGUST 1993, INCORPORATE LIVING
RESOURCES  HABITAT  GOALS  INTO  TRIBUTARY-SPECIFIC
NUTRIENT REDUCTION STRATEGIES.

1.2. Provide  educational and informational  aids to support and
reinforce the ecosystem-based approach,  as well as recognition and
understanding of the importance of ecologically valuable species.
Much is yet to be learned about the structure and functions
of the Chesapeake ecosystem. Implementation of recommen-
dation  1.1. will be facilitated by ensuring that sound con-
cepts of the structure and functions of the Bay ecosystem
are  shared  by those who plan,  make, and  implement Bay
Program decisions. This Strategy is a first step toward this
goal.  More compact  and  accessible tools  are  needed,
however. First,  to communicate these ideas to the  public;
second,  to sustain the  use of these concepts in the Bay deci-
                                                                                                                    11

-------
sion-making process;  third,  to  provide  ready  access  to
information, such as the status of ecosystem indicators and
the potential for changes in one component of the ecosys-
tem to affect other components.

1.2.1 Inform the public of this Strategy and its objectives, and the
recommendations for reaching the ultimate goal to restore a more
balanced ecosystem in Chesapeake Bay.

ACTION ITEM:  BY DECEMBER 1992,  PUBLISH  A BRIEF,
ILLUSTRATED SYNOPSIS OF THIS STRATEGY  AS A PUBLIC
INFORMATION AID.

1.2.2.  A poster illustrating ecosystem  community relationships
should be published and made available to managers.
The poster should be both accurate and attractive,  therefore
it will require peer review and professional graphics design.
The poster should be distributed to Bay managers  and staff
along with a lecture and discussion, and made available to
educational institutions and the public. A software version
of  the poster, keyed  to  a)  ecosystem  indicators and their
status, and b) descriptive information, should be considered
as a longer term objective.

ACTION ITEM:  BY MAY  1994, DESIGN  AND  PUBLISH A
POSTER THAT SHOWS THE MAJOR COMPONENTS  OF THE
CHESAPEAKE ECOSYSTEM  AND HOW THEY ARE INTERCON-
NECTED BASED UPON A GENERALLY ACCEPTED CONCEPTUAL
MODEL

2. Ecosystem simulation and analysis
2.1. Pursue a long-term program to develop simulation models of
the  Chesapeake ecosystem  to link resource management, habitat
restoration and pollution reduction and prevention.
The many interactions between species, habitats, human
uses, and  management cannot be understood or quantified
without models that incorporate the many processes that
link these ecosystem components. It is especially important
for many of the ecologically valuable  species that  their
interactions  with  managed  species (as  prey,  predators,
competitors, or habitat formers) be quantified.  Plans  for
management of harvested species  and  habitats  require a
common, ecologically sound basis to ensure that they work
together, rather than in parallel and possibly in opposition.
For example, a  coastal fisheries model that considers multi-
ple species has been shown to  contradict the conclusions of
a single-species  model, to the potential detriment of  the
fishery and to populations of several other species (Muraw-
ski  1991).

2.1.1.  The early phases of ecosystem simulation should  include a
variety of approaches to the problems of modeling such a complex
system.
Bottom-up and top-down modeling concepts (see the section
VlSION-TOWARD   A  BALANCED  ECOSYSTEM),   network
analysis  (Baird and  Ulanowicz  1989),  spatial  analysis
(Costanza et al. 1990), bioenergetics models, individual-based
models,  and  statistical  extrapolations from  long  term
databases (e.g., Vaas and  Jordan 1991) all have validity as
ecosystem  simulation  tools,  relating  to  environmental
properties  and subject  to trend analyses. All are  presently
being applied in some  manner to address questions about
the Chesapeake ecosystem or its components. Another way
to characterize an  ecosystem is by using functional groups.
A promising way  to characterize functional groups and to
quantify their role in ecosystems, is through analysis of food
web patterns  and  dynamic properties.  By integrating dy-
namic properties such as growth, mortality, production and
recruitment, and combining this data with bioenergetics re-
search, models could lead to an understanding of cause and
effect relationships. At  this  early stage of numerical model-
ing of complex ecosystems,  a multi-faceted approach is pru-
dent because  it ensures that the many-dimensional system
will be viewed  from many directions, and  increases the
probability that necessary questions will be asked.
2.1.2. Coordinate ecosystem modeling efforts to ensure convergence
of the several modeling approaches being pursued.  Facilitate collab-
oration  between  researchers, modelers, and statisticians.  Coor-
dination needs to be maintained both among investigators and
among funding agencies.
The goal of obtaining consistent, valid answers to  questions
about the ultimate effects of management actions on the
Chesapeake ecosystem must  be  kept in sight. Towards this
end,  a generic modeling  framework, capable of accommo-
dating  different approaches to subsystems  of the overall
model, has been adopted  by the participants in the present
tributary (Patuxent and York Rivers)  pilot projects. Coor-
dination must be maintained through regular meetings and
discussions among investigators and managers. In addition,
models involving living resources will call on  the expertise
of both the Living Resources and  Modeling Subcommittees
to reach their full potential.  Coordination and cooperation
between these two groups are essential.

2.2.  Convene a series of scientific workshops to build consensus on
conceptual and technical issues  involved in ecosystem simulation.
At least one intensive workshop should be held,each year.
The  first  of these workshops (Chesapeake Bay Ecosystem
Processes Workshop) was held in March 1992. The next one
is scheduled for July, 1993.

3. Habitat Restoration and Maintenance
3.1. Develop a comprehensive and integrated habitat restoration
strategy for Chesapeake Bay.
Habitat restoration and maintenance need to be addressed
through a comprehensive,  integrated management  plan.
12

-------
Some  major habitat  considerations (SAV restoration, wet-
lands  protection,  barriers to  fish  migration, dissolved
oxygen and SAV habitat requirements) have been addressed
by plans  or  syntheses  of  habitat  requirements  (CEC
1988a,b,c; 1989; 1990; Jordan et d. 1992; Batiuk et al  1992).
Structural habitat needs have been identified and described
for selected  Bay species  (Funderburk et al. 1991). All of
these efforts, applied as intended, will benefit ecologically
valuable species.

Additional habitat restoration and protection efforts are
being undertaken, or  have been proposed (e.g.,  use of waste
materials to rebuild reef and shallow water habitats).  Other
important habitat needs, although they may be addressed by
various state and  Federal programs, have not  come  under
the guidance of Bay-wide  plans;  for example,  the need to
conserve and restore critical  shoreline habitats  (wooded
shores for raptors and wildlife, sandy beaches for diamond-
back terrapin nesting, intertidal foraging areas  for seabirds
and wading birds, etc.). An integrated  habitat management
plan would help greatly to set priorities, avoid conflicts and
dilution of effort, and build  the programmatic structure
necessary to implement a fully coordinated habitat restora-
tion and management program for  the Bay.  The  plan
should consider all aspects of habitat management, regard-
less of where current  responsibilities may lie.

3.2. Compile habitat requirements for selected ecologically valuable
species and species assemblages.
A supplement to Habitat Requirements for Chesapeake Bay Liv-
ing Resources (Funderburk et al. 1991) should be developed,
with  emphasis  on  non-economic  living  resources.  For
example, chapters on  phytoplankton,  zooplankton, forage
fish,  and benthic assemblages  would  help  to assemble
information  necessary to meet some of the recommenda-
tions  of this strategy (e.g., ecosystem  indicators, planning
for habitat  management). Such  a document  also  would
identify  research needs and be an important  educational
tool.

4. Ecosystem indicators
Biological indicators of ecosystem integrity will be needed
to measure progress towards the  goals of the  1987 Chesa-
peake  Bay Agreement. The geographical,  temporal, and
biological complexity of the Bay will require  a system of
indicators, rather than any single indicator. The necessary
data are theoretically available from the Bay's  comprehen-
sive  living resources  monitoring program (CEC  1988b),
however, additional work will be needed to implement such
a system.


4.1. Develop and implement a consistent system of indicators of
ecosystem integrity for Chesapeake Bay.
This recommendation should be  met through  a consensus
 process, overseen by the Chesapeake Bay Living Resources
 Subcommittee, within a year after adoption of the Strategy.
 The development of a consistent system will rely on a full
 understanding of  the  strengths and weaknesses  of each
 biological indicator.

 Candidate habitat indicator statistics are found in Table 2
 and the section DESCRIPTION AND STATUS OF ECOSYSTEM
 INDICATORS. Recommendations for application and further
 development of the indicators that appear most promising,
 based upon use and interpretation of existing monitoring
 data,  are  currently  being -generated  by  several  groups
 connected with the Chesapeake Bay Program. Habitat indi-
 cator statistics should be reported routinely (e.g., State of the
 Bay Report), both Bay-wide and for individual Bay segments.
 The list in Table 2 is intended to be neither inclusive nor
 exclusive;  it specifies indicators known to the work group
 that  are  immediately available or  in  advanced  stages of
 development.

 4.2. Establish target levels for ecosystem indicators on a tributary-
 specific basis. These target levels will be used to set goals for
 nutrient and pollutant control strategies.

 4.3. Develop, evaluate, and apply additional multi-species statistics
 as indicators of status and trends in the structure and function of
 the Chesapeake ecosystem.
 It is  important to  avoid  isolated interpretation of single-
 species statistics  in  an ecosystem  context.  Single-species
 statistics (e.g., Maryland and Virginia striped bass juvenile
 indices; Maryland oyster spat index; Bay-wide waterfowl and
 raptor counts) are  useful  for their intended purposes  in
 managing  the species. However, they sometimes are inter-
 preted as indicators  of system health, for which  purpose
 they  generally  are  not  robust, as  discussed above in  the
 Status of Ecosystem Indicators section. Because of the com-
 plexity of the  estuarine system and the diversity of species
 in the Chesapeake Bay, a functional group  approach for
 each major salinity region is essential.
4.4. Continue to use SAV acreage as a key ecosystem indicator
statistic.
The only multi-species indicator currently in general use for
Chesapeake Bay is SAV acreage, which is  monitored and
reported on an annual basis.
ACTION ITEM: BY JUNE 1994, PUBLISH A HANDBOOK OF
ACCEPTED ECOSYSTEM INDICATORS FOR CHESAPEAKE BAY,
INCLUDING INFORMATION ON MEASUREMENT AND INTER-
PRETATION. A  COMPREHENSIVE MATRIX DETAILING THE
STRENGTHS AND WEAKNESSES OF EACH ECOSYTEM INDICA-
TOR, AND A KEY OF USEFUL INTERPRETATIONS OF SINGLE-
SPECIES STATISTICS WILL BE INCLUDED.
                                                                                                                    13

-------
5. Monitoring
The  Chesapeake Bay  Living Resources  Monitoring  Plan
(CEC  1988b) adopted  an ecosystem perspective  in devel-
oping recommendations for Bay-wide biological monitoring.
Success in meeting the objectives of this strategy will depend
heavily upon the  continued availability of the compre-
hensive data generated by the monitoring programs.

5.1.  Establish a  stable,  long-term funding mechanism for key
living resources monitoring programs.
Such core elements of the program as SAV and zooplankton
monitoring  have faced  annual struggles to obtain  the
funding  necessary  to  continue  them.  This situation  has
arisen  because the potential of the existing  data has  not
been fully realized, and because consistent time series  of 5-
10 years  are  necessary in  a  system as large and complex as
Chesapeake Bay in order to  establish baselines against which
to measure system health and progress  towards restoration.
In setting funding priorities, it should be understood  that
the value of monitoring programs of this  type  generally
increases steadily with the length of the time series.

6. Data management and analysis
Several of the recommendations above  will depend heavily
on data management and analysis for their implementation.
Development and application of biological indicators  and
ecosystem  simulation  models will  require comprehensive.
well-managed, and  accessible data. Monitoring  programs
cannot serve their functions without sufficient attention to
data management and analysis.

6.1. Publish a directory and user's manual for the Chesapeake Bay
living resources database.
The  Chesapeake Bay Program has put a great deal of effort
into the acquisition of data sets on many living resources,
quality assurance of those sets and their incorporation into
a database. This  database is generally accessible  to  knowl-
edgeable users, but is not well known to many who could
make good use of it. The directory should be designed and
distributed so as to facilitate its use by researchers.  It should
specify procedures  for downloading and communicating
data to  various kinds  of storage  media and   computer
systems.

6.2. Develop data sets from the living resources database to match
specific  questions and intended outputs (e.g., ecosytem indicators).
Well-focused, management-oriented questions can  guide the
structures of data  sets. For example,  management needs
recently have stimulated development of specific data sets
for synthesis of SAV and dissolved oxygen habitat require-
ments. Once a consensus system of biological  indicators is
established  (Recommendation  4.1),  the  living  resources
database  can be structured  for efficient calculation of
indicator statistics and comparisons with  other (e.g., water
quality) data.
6.3. Ensure support and direction for data analysis.
In general, monitoring programs and research grants  and
contracts  provide support  for data collection and analysis
for specific  purposes. Seldom is there  sufficient time or
funding available  to apply the  data to its  full  potential,
especially  for some  of the  purposes  important to  this
strategy. One of the reasons monitoring programs often fail
to fulfill their promise  is because analysis  is a "spare time"
effort. The  generation  of  important information can be
overlooked or delayed.

Recently,  the Chesapeake Bay Monitoring  and Living
Resources Subcommittees  have  jointly proposed  analytical
work on statistical power and trends for Bay-wide biological
monitoring  data. This effort should be supported.

7. Research
Research has a role in any strategy related to  the recovery of
a  biological community.   This  is particularly  true  for
ecologically  valuable  species.  Research and  monitoring
complement and supplement each other, especially for those
species  which are not covered  by fisheries management
plans. Research  should increase our knowledge of habitat
requirements, life histories, and interrelationships among
species, communities, and  functional groups.

The  experts who contributed   to  this strategy included
recommendations for further work in monitoring, research,
modeling, habitat and management, as well as some general
recommendations for changes in our approach to studying
the Chesapeake  Bay ecosystem (see Appendix B). Using this
list as the starting point, the Bay Program should be able to
define new  research needs  and prioritize them.

7. /. Provide  expanded opportunities for research into the life histo-
ries, ecological associations, functional roles,  and habitat require-
ments of ecologically valuable species.
Solid research programs for planktonic and benthic biota
have been maintained in Chesapeake Bay (partially benefited
by the Bay-wide monitoring program). But it is notoriously
difficult for scientists to gain support for basic  biological
and  ecological  research  on  many other  non-economic
species. Funding agencies  and managers  of research  pro-
grams should encourage research into functions and interre-
lationships  of species  and species  groups which have re-
ceived inadequate  attention.  This research will help  to
support model development and further understanding of
the Bays  complex web of  life.

7.2.  Develop a list of priority  research topics oriented towards
ecologically valuable species and communities.
Research managers often look for authoritative guidance in
developing and tuning their programs. Sometimes too much
emphasis  is put on economically valuable species in both
 14

-------
generic  and special  purpose research programs.  The rec-
ommended consensus list will help to remedy this situation.
The  Chesapeake  Bay  Program  Scientific  and  Technical
Advisory Committee should oversee this project.
                                                                                                                 15

-------
                               EVS
             ACTION ITEM
 TIME FRAME
          RESPONSIBILITY
 1. General recommendations
 1.1.  Develop the mechanism to make this
 Strategy a framework for coordination of the
 various fisheries management plans, water-
 fowl management plans, habitat restoration
 plans, ana other Chesapeake Bay Program
 plans, promoting cross-program integration
 throughout the Chesapeake Bay Program.

 1.1.1. Pursuant  to the schedule  of  fishery
 management plan re-evaluations, revise  or
 amena selected fishery management plans to
 include all available information on the effects
 of fisheries on the ecosystem.

 1.1.2. Incorporate living resources  habitat
 goals into tributary-specific nutrient reduction
 strategies.

 1.2.  Provide  educational and informational
 aids to support and reinforce the ecosystem-
 based approach, as well as recognition and
 understanding of the importance of ecologi-
 cally valuable species.

 .1.2.1. Publish a brief, illustrated synopsis  of
 this Strategy as a public information aid.
to be determined
Ecologically Valuable Species Workgroup
(Jordan)
refer to FMP sched-
ule
August 1993
December 1992
Ecologically Valuable Species Workgroup
(Jordan)   /  Fisheries   Management
Workgroup (Jensen)
Living Resources Nutrient Reevaluation
Task Force
Ecologically Valuable Species Workgroup
(Cresswell)
1.2.2.  Design and  publish  a poster that
shows the major components of the Chesa-
peake ecosystem and how they are intercon-
nected based upon  a generally accepted
conceptual model.
May 1994
Ecologically Valuable Species Workgroup
and NOAA (Gillelan)
2. Ecosystem simulation and analysis

2.1. Pursue a long-term program to develop
simulation models of the Chesapeake eco-
system to link resource management, habitat
restoration and pollution reduction and pre-
vention.

2.1.1. The early phases o\ ecosystem simula-
tion should include a variety of approaches to
the problems of  modeling  such a complex
system.

2.1.2. Coordinate ecosystem modeling efforts
to ensure convergence of the several model-
ing approaches being pursued.

2.2. Convene a series of scientific workshops
to build consensus on conceptual and techni-
cal issues involved in ecosystem simulation.
At least one intensive workshop should be
held each year.
on-going
on-going
on-going
Ad  Hoc Ecosystem  Modeling  Panel
(Batiuk / Jordan / Linker)
Ad  Hoc Ecosystem  Modeling  Panel
(Batiuk / Jordan / Linker)
Scientific and Technical Advisory Com-
mittee
 16

-------
 3. Habitat  Restoration  and (Mainte-
 nance
3.1. Develop a comprehensive and integrated
habitat restoration strategy for the Chesa-
peake Bay.

3.2. Compile habitat requirements for select-
ed ecologically valuable species and species
assemblages.

4. Ecosystem indicators

4.1.  Develop and implement a consistent
system of indicators of ecosystem integrity for
Chesapeake Bay.

4,1.1. Publish a handbook of accepted eco-
system  indicators  for  Chesapeake  Bay,
including information on measurement and
interpretation.
December 1993
to be determined
June 1994
Habitat   Objectives/Restoration
Workgroup (Funderburk)
Ecologically Valuable Species Workgroup
(Jordan)
Ecologically Valuable Species Workgroup
(Jordan)/Monitoring  Workgroup of the
Living  Resources  Subcommittee (Bu-
chanan)
4.2.  Establish target levels  for ecosystem
indicators on a tributary-specific basis.
4.3. Develop, evaluate, and apply additional
multi-species statistics as indicators of status
and trends in the structure and function of
the Chesapeake ecosystem.

4.4. Continue to use SAV acreage as a key
ecosystem indicator statistic.

5.

5.1. Establish a stable, long-term funding
mechanism for key living resources monitor-
ing programs.

6.

6.1. Publish a directory and user's manual for
the Chesapeake Bay living resources data-
base.

6.2. Develop data sets from the  living re-
sources database to match specific questions
and intended outputs (e.g., ecosystem indica-
tors).

6.3. Ensure support and direction for  data
analysis.

7. Research

7.1. Provide expanded opportunities for re-
search into the life histories, ecological asso-
ciations, functional roles, and habitat require-
ments of ecologically valuable species.

7.2. Develop a list of priority research topics
oriented towards ecologically valuable  spe-
cies and communities.
to be determined
to be determined
on-going
on-going; year to
year
to be determined
on-going
on-going
on-going
October 1993
Ecologically Valuable Species Workgroup
(Jordan)/Monitoring  Workgroup of the
Living  Resources  Subcommittee (Bu-
chanan)

Ecologically Valuable Species Workgroup
(Jordan)/ Monitoring  Workgroup  of the
Living  Resources  Subcommittee (Bu-
chanan)

SAV Workgroup (Pendleton)/ Living Re-
sources Monitoring Workgroup (Buchan-
an)
Living Resources Subcommittee
Data Acquisition Workgroup
Living Resources Monitoring Workgroup
(Buchanan)
Data Analysis Workgroup (Magnien)
Scientific and Technical Advisory Com-
mittee
Scientific and Technical Advisory Com-
mittee (Watkins)
                                                                                                  17

-------
                                               REFERENCES
Baird, D. and R.E. Ulanowicz. 1989. The seasonal dynamics
of the Chesapeake  Bay ecosystem. Ecological Monographs
59(4): 329-364.

Batiuk, R.A.,  R.J. Orth, K.A. Moore, W.C. Dennison, J.C.
Stevenson,  L.W. Staver,  V. Carter,  N.B.  Rybicki,  R.E.
Hickman, S.  Kollar,  S. Bieber, and P.Heasly. 1992. Ches-
apeake Bay submerged aquatic vegetation habitat  require-
ments and restoration targets: a technical synthesis. Chesa-
peake Bay Program. CBP/TRS 83/92. Annapolis, Maryland.

Buchanan, C. 1992. Chesapeake Bay zooplankton monitor-
ing:  report on a  workshop  held  in Easton, Maryland,
September 23-24, 1991. Prepared by the Interstate Commis-
sion on the Potomac River Basin and the Maryland Depart-
ment of the Environment for the Living Resources Subcom-
mittee, Chesapeake Bay Program.

Cargo, D.G., J.H, Turtle and R.B. Jonas. 1986. The  low dis-
solved oxygen situation in the Chesapeake  Bay: then and
now. Spring Meeting. AERS. Lewes, DE.

Carter, V., J.W. Barko, G.L. Godshalk, and N.B. Rybicki.
1988. Effects of submersed macrophytes on water quality in
the tidal  Potomac  River,  Maryland. Journal of Freshwater
Ecology 4(4):  493-501.

Cooper, S.R.  and G.S. Brush.  1991. Long-term history of
Chesapeake Bay anoxia. Science 254: 992-995.

CEC (Chesapeake  Executive Council). 1988a. Chesapeake
Bay  Wetlands  Policy.  Agreement  Commitment  Report.
Annapolis, Maryland.

CEC (Chesapeake  Executive   Council).  1988b.   Living
Resources  Monitoring   Plan.   Agreement  Commitment
Report. Annapolis, Maryland.

CEC (Chesapeake Executive Council). 1988c. Strategy for
Removing Impediments to Migratory Fishes in the Chesa-
peake Bay Watershed. Agreement Commitment Report. An-
napolis, Maryland.

CEC (Chesapeake  Executive Council).  1989.  Submerged
Aquatic Vegetation Policy for the Chesapeake Bay and Tidal
Tributaries. Agreement Commitment Report.  Annapolis,
Maryland.

CEC (Chesapeake Executive Council). 1990. Implementation
Plan for  the  Submerged Aquatic Vegetation Policy. Agree-
ment Commitment Report. Annapolis, Maryland.
Costanza, R., F.H. Sklar, and  M.L White. 1990. Modeling
coastal landscape dynamics. Bioscience 40(2): 91-107.

Dennison, W.,  R. Orth,  K.A. Moore, J.C. Stevenson, V.
Carter, S. Kollar,  P.W.  Bergstrom and  R. Batiuk.  1993.
Assessing water quality with submersed aquatic vegetation:
habitat  requirements  as  barometers  of Chesapeake  Bay
health. Bioscience 43(2):86-94.

Erwin, R.M.  and J.A. Spendelow. 1991. Colonial wading
birds:  Herons  and  egrets.  In:  S.L.  Funderburk,  J.A.
Mihursky, S.J. Jordan, and D. Riley (eds.) Habitat Require-
ments for Chesapeake Bay  Living Resources. 2nd  edition,
pp. 19-1 to 19-14.

Fewlass, L 1991. Statewide fisheries survey and management,
study V: Investigations of Largemouth  Bass populations
inhabiting  Maryland's tidal waters.  Final  report F-29-R.
Maryland Department of Natural Resources.

Funderburk, S.L.,  J.A. Mihursky, S.J. Jordan, and D. Riley
(eds.). 1991. Habitat Requirements for Chesapeake Bay Liv-
ing Resources. 2nd edition.

Homer, M.L. and J. Mihursky. 1991. Spot. In: S.L.  Funder-
burk, J.A. Mihursky, S.J. Jordan, and D. Riley (eds.). Habitat
Requirements for Chesapeake Bay Living  Resources.  2nd
edition, pp. 11-1 to 11-19.

Houde,  E.D. and  C.E. Zastrow. 1991.  Bay anchovy. In: S.L.
Funderburk, J.A. Mihursky, S.J. Jordan, and  D. Riley (eds.).
Habitat Requirements for Chesapeake  Bay Living Resources.
2nd edition, pp. 8-1 to 8-11.

Hurley, L.M. 1991.  Submerged aquatic vegetation. In: S.L.
Funderburk, J.A. Mihursky, S.J. Jordan, and  D. Riley (eds.).
Habitat Requirements for Chesapeake  Bay Living Resources.
2nd edition, pp. 2-1 to 2-19.

Jordan,  S.,  C. Stenger,  M.  Olson,  R.  Batiuk,  and  K.
Mountford.  1992. Chesapeake Bay Dissolved Oxygen Goal
for Restoration of Living Resource  Habitats. Chesapeake
Bay Program CBP/TRS 88/93. Annapolis, Maryland.

Luckenbach,  M.W., R.J. Diaz, and  L.C.  Schaffner. 1988.
Benthic assessment procedures. In: Cooperative State Agency
Program Annual Report Fiscal  Year 1987-1988.  Virginia
Institute of Marine Sciences, Gloucester Point.

Malone, T.C., W.M. Kemp, H.W. Ducklow,  W.R. Boynton,
J.H. Tuttle, and R.B. Jonas. 1986. Lateral variation  in the
18

-------
production  and  fate  of  phytoplankton  in  a  partially         PSC (Principals'  Staff Committee).  1990. Chesapeake Bay
stratified estuary. Marine Ecology Progress Series 32: 149-         Wetlands  Policy  Implementation  Plan.  Implementtation
160.                                                            Plan. Annapolis,  Maryland.

Maxted, J.R. 1990. The development of biocriteria in marine         Vaas, P.A. and S.J. Jordan.  1991. Long-term trends in abun-
and estuarme waters in  Delaware, in Water  Quality Stan-         dance indices for 19 species of Chesapeake Bay fishes: reflec-
dards for the 21st Century, Proceedings. December 10-12,         tions of trends in the Bay ecosystem. In: J.A.  Mihursky and
1990, Arlington, Virginia.                                        A.  Chaney  (eds.),  New  Perspectives  in the  Chesapeake
                                                                System: A  Research  and Management Partnership. Proceed-
Murawski, S.A. 1991. Can we manage our multispecies fish-         ings of a Conference. 4-6 December 1990. Baltimore, MD.
cries? Fisheries 16(5): 5-13.                                       Chesapeake Research Consortium Publication No. 137.
                                                                                                                   19

-------

-------
                                                             A

Ecologically valuable species and species groups of the Chesapeake Bay. Bacteria groups were identified by J. Tuttle,
Chesapeake Biological Laboratory. Phytoplankton and zooplankton species were selected after careful discussions with
scientists familiar with the Chesapeake Bay planktonic communities.  The benthic infauna  listed are representative
assemblages  of each salinity  zone. The benthic epifaunal species  are  those representative of the mesohaline
Chesapeake Bay. Fish species were chosen based on a minimum CPUE (catch per unit effort) of 0.1 in Maryland seine
and  bottom  trawl samples (Carmichael  et  al. 1992) or from consultation with biologists for those species not
represented in seine and trawl samples (notably reef fishes). Waterfowl species listed here were chosen for their degree
of dependence on the living resources of the Chesapeake Bay. Vegetation species, both submerged and emergent, are
separated into representative assemblages for each salinity zone. The  groups of species listed here are meant to be
representative rather than inclusive. In all groups, most of the species are indicative of a well-balanced system. All
others, where high abundances may indicate  problems, are marked with a superscript: 1 = pollution  tolerant, 2 =
indicative of eutrophication, 3  = exotics, i.e. non-native species.
                                                                                                         21

-------

-------
 Bacteria
  heterotrophic aerobes1'2
  sulfate reducers1-2

 Phytopiankton
 TIDAL FRESHWATER
  Anacystis spp. (cyanobacteria)2
  Aphanizomenon flos-aquae
       (cyanobacteria)2
  Asterionella lormosa (diatom)
  Chroococcus limneticus (cyanobacteria)
  Cyclotella meneghiniana (diatom)
  Cydotella striata (diatom)
  Melosira distans (diatom)
  Melosira granulata (diatom)
  Merismopedia tenuissima (cyanobacteria)
  Microcystis aeruginosa (cyanobacteria)2
  Scenedesmus spp. (chlorophyte)
  Skeletonema potamos (diatom)
 OLIGOHAUNE
  Cerataulina pelagica (diatom)
  Ceratium spp. (dinoflagellate)
 Cryptomonas spp. (cryptomonad)
 Cyclotella striata (diatom)
 Gymnodinium spp. (dinoflagellate)2
 Gyrodinium uncatenum (dinoflagellate)2
 Melosira distans (diatom)
 Melosira granulata (diatom)
 Microcystis aeruginosa (cyanobacteria)2
 Skeletonema potamos (diatom)
 MESOHALINE
 Asterionella glacialis (diatom)
 Cerataulina pelagica (diatom)
 Ceratium spp. (dinoflagellate)
 Cryptomonas spp. (cryptomonad)
 Cyclotella caspia (diatom)
 Gymnodinium spp. (dinoflagellate)2
 Gyrodinium uncatenum (dinoflagellate)2
 Heterocapsa triquetra (dinoflagellate)
 Katodinium rotundatum (dinoflagellate)
 Leptocylindrus minimus (diatom)
 Promcentrum minimum (dinoflagellate)
 Rhizosolenia fragilissima (diatom)
 Skeletonema costatum (diatom)
 POLYHALINE
 Asterionella glacialis (diatom)
 Cerataulina pelagica (diatom)
 Ceratium lineatum (dinoflagellate)
 Chaetoceros spp. (diatom)
 Gymnodinium spp. (dinoflagellate)2
 Gyrodinium uncatenum (dinoflagellate)2
 Leptocylindrus minimus (diatom)
 Leptocylindrus danicus (diatom)
 Prorocentrum micans (dinoflagellate)
 Rhizosolenia alata (diatom)
 Rhizosolenia stolterfothii (diatom)
 Skeletonema costatum (diatom)
 Thalassionema nitzschioides  (diatom)

Zooplankton
 Euplotidae (protozoans)2
 Tintinnidium (protozoans)
 Synchaeta sp. (rotifers)
 Brachionus sp. (rotifers)2
 Bosmina longirostris (dadoceran)2
  Leptodora kindtii (cladoceran)
  Acartia tonsa (copepod)
  Eurytemora affinis (copepod)
  Chrysaora quinquecirrha (sea nettle)
  Mnemiopsis leidyi (sea walnut)
  Nemopsis bachei (hydroid)
  larval fish
  polychaete larvae
  barnacle larvae

 Benthic Infauna
 TIDAL FRESHWATER
  llyodrilus spp. (oligochaete)
  Limnodrilus spp. (oligochaete)
  Naididae (oligochaetes)
  Corbicula fluminea (bivalve)3
  Musculium spp. (bivalve)
  Polypedilum spp. (insect)
  Chironimidae larvae (insect)1
  Chaoboridae larvae (insect)
 OLIGOHAUNE
  Rangia cuneata (bivalve)3
  Marenzellaria viridis (polychaete)
  Cyathura polita (isopod)
  Gammarus daiberi (amphipod)
  Carinoma spp. (nemertean worm)
  Gemma spp. (bivalve)
  Tagelus spp. (bivalve)
 Eteone spp. (polychaete)
  Tubificoides spp. (polychaete)1
 Asabellides spp.  (polychaete)
 Mysidopsis spp. (crustacean)
 MESOHALINE
 Macoma mitchelli (bivalve)
 Macoma balthica (bivalve)1
 Mya arenaria (bivalve)
 Mulinia lateralis (bivalve)
 Parvilucina spp.(bivalve)
 Leptocheirus plumulosus (amphipod)
 Leucon americanus (cumacean)
 Monoculodes spp. (crustacean)
 Glycinde spp. (polychaete)
 Nereis succinea (polychaete)
 Strebliospio benedicti (polychaete)
 Heteromastus filiformis (polychaete)
 Micrura spp. (nemertean worm)
POLYHALINE
 Ascyhis elongata (polychaete)
 Clymenella torquata (polychaete)
 Macroclymene zonalis (polychaete)
 Chaetopterus variopedatus (polychaete)
 Diopatra cuprea (polychaete)
 Glycera americana (polychaete)
 Loimia medusa (polychaete)
 Leitoscoloplos spp. (polychaete)
 Notomastus spp.  (polychaete)
 Mediomastus ambiseta (polychaete)
 Spiochaetopterus spp. (polychaete)
 Paraprionospio pinnata (polychaete)
 Pseudeurythoe
     paucibranchiata (polychaete)
 Spiophanes bombyx (polychaete)
 Nephtys picta (polychaete)
 Upogebia affinis (decapod)
 Mercenaria mercenaria (bivalve)
  Ensis directus (bivalve)
  Gemma gemma (bivalve)
  Cerianthus americanus (anemone)
  Tellina agilis (bivalve)

 Benthic Epifauna
  barnacles
  sponges
  Crassostrea virginica (oyster)
  Brachidontes recurvus (bent mussel)
  Electra crustulenta (bryozoan)
  Membranipora tenuis (bryozoan)
  Molgula manhattensis (tunicate)
  Polydora ligni (mud worm)
  Polydora websteri (oyster worm)
  Corophium lacustre (amphipod)
  Callinectes sapidus (blue crab)
  Eurypanopeus depressus (mud crab)
  Panopeus  herbsti (mud crab)
  Styiochus ellipticus (flatworm)

 Fish
 MARINE SPAWNERS
 Anguilla rostrata (American eel)
 Bairdiella chrysaura (silver perch)
 Brevoortia  tyrannus (Atlantic menhaden)1'2
 Cynoscion  nebulosus (spotted seatrout)
 Cynoscion  regalis (weakfish)
 Leiostomus xanthurus (spot)2
 Micropogonias undulatus (Atlantic croaker)
 Paralichthys dentatus (summer flounder)
 Peprilus alepidotus (harvestfish)
 Pogonias cromis (black drum)
 Pomatomus saltatrix (bluefish)
 Sciaenops  ocellatus (red drum)
 Stronglyura marina (Atlantic needlefish)
 ESTUARINE RESIDENT
 Anchoa mitchilli (bay anchovy)
 Cynoscion  nebulosus (spotted seatrout)
 Cynoscion  regalis (weakfish)
 Cyprinodon variegatus  (killiflsh)
 Fundulus diaphanus (banded killifish)
 Fundulus heteroclitus (mummichog)1
 Fundulus majalis (striped  killifish)
 Hypognathus regius (silvery minnow)1
 Lepomis gibbosus (pumpkinseed)
 Membras marinica (rough silversides)
 Menidia beryllina (tidewater silversides)
 Menidia menidia (Atlantic  silversides)
 Notropis hudsonius (spottail shiner)
 Paralichthys dentatus (summer flounder)
 Pseudopleuronectes americanas (winter
         flounder)
 Rhinoptera bonasus (cownose ray)
 Syngnathus (uscus (northern pipefish)
 Trinectes maculatus (hogchoker)
ANADROMOUS
 Alosa aestivalis (blueback herring)
 Alosa mediocris (hickory shad)
 Alosa pseudoharengus (alewife)
 Alosa sapidissima (American shad)
 Morone americana (white  perch)
 Morone saxatilis (striped bass)
 Perca flavescens (yellow perch)
TIDAL FRESHWATER
                                                                                                                             23

-------
 Cyprinus carpio (carp)
 Dorosoma cepedianum (gizzard shad)1'2'3
 Etheostoma olmstedi (tesselated darter)
 Fundulus diaphanus (banded killifish)
 Hypognathus regius (silvery minnow)1
 Ictalurus catus (white catfish)
 Ictalurus nebulosus (brown bullhead)
 Ictalurus punctatus (channel  catfish)
 Lepomis gibbosus (pumpkinseed)
 Lepomis macrochirus (bluegill)
 Menidia beryllina (tidewater silversides)
 Micropterus salmoides (largemouth bass)
 Notropis hudsonius (spottail shiner)
REEF FISH
 Centropristis striata (black sea bass)
 Chasmodes bosquianus (striped blenny)
 Gobiesox strumosus (skilletfish)
 Gobiosoma bosci (naked goby)
 Opsanus tau (oyster toadfish)

Waterfowl
 Aix sponsa (wood duck)
 Anas rubripes (black duck)
 Anas americana (American widgeon)
 Aythya affinis (lesser scaup)
 Aythya americana (redhead duck)
 Aythya mania (greater scaup)
 Aythya valisneria (canvasback)

Submersed Aquatic Vegetation
POLYHALINE
 Zostera marina (eelgrass)
 Ruppia maritima (widgeongrass)
 Zannichellia palustris (horned
     pondweed)1-2
MESOHALINE
 Zostera marina (eelgrass)
 Ruppia maritima (widgeongrass)
 Zannichellia palustris (horned
     pondweed)1-2
 Potamogeton pectinatus (sago pondweed)
 Potamogeton perfoliatus (redhead grass)
 Myriophytlum spicatum (water milfoil)2
 Vallisneria americana (wild celery)
OLIGOHAUNE/FRESHWATER
 Ruppia maritima (widgeongrass)
 Potamogeton pectinatus (sago pondweed)
 Potamogeton perfoliatus (redhead grass)
 Myriophyllum spicatum (water milfoil)2
 Vallisneria americana (wild celery)
 Heteranthera dubia (water stargrass)
 Hydtilla vertidllata (hydrillap
 Elodea canadensis (common elodea)
 Ceratophyllum demersum (coontail)
 A/a/as guadalupensis (southern naiad)
 Zannichellia palustris (horned
     pondweed)1'2

 Emergent Vegetation
 TIDAL FLATS
 Ulva lactuca (sea lettuce)
 COASTAL MARSHES
 High salinity
 Spartina alterniflora (saltmarsh cordgrass)
 Spartina patens (saltmeadow hay)
 Low Salinity
 Scirpus olneyi (olney threesquare)
 Spartina cynosuro/des (big cordgrass)
 Tidal Fresh
 Pontederia cordata (pickerelweed)
 Zizania aquatica (wild rice)
FRESHWATER EMERGENT WETLANDS
 Scirpus validus (softstemmed bulrush)
 Bidens cernua (nodding bur marigold)
 Chelone glabra (turtlehead)
 Cicuta maculata (water hemlock)
 Hypericum vergicum (St. Johnswort)
 Justicia americana (water willow)
 Lycopus virginicus (water horehound)
 Mimulus ringens (square-stemmed
       monkeyflower)
 Phragmites austra/is (reed grass)1'37
 Typha latifolia (common cattail)1'2
SHRUB WETLANDS
 Alnus serrulata (common alder)
 Asimina triloba (paw paw)
 Cephalanthus occidentalis (buttonbush)
 Rhododendron viscosum (azalea)
 Myrica cerifera (southern wax myrtle)
FORESTED WETLANDS
 Acer rubrum (red maple)
 Chamaecyparis thyoides (Atlantic white
     cedar)
 Betula nigra (river birch)
 Fraxinus pensylvanica (red ash)
 Nyssa sylvatica (black gum)
 Taxodium distichum (bald cypress)
FRESHWATER PONDS
 Nuphar luteum (yellow pond lily)
 Myriophyllum spicatum (eurasian
     watermilfoil)2
 Lemna minor (lesser duckweed)2
 24

-------
                                                              B

The following technical documents give the perspectives of research scientists on the Chesapeake Bay ecosystem. The
Strategy for the Restoration and Protection of Ecologically Valuable Species emphasizes cooperation between managers,
researchers and modelers. In this Appendix, each scientist gives his or her viewpoint on the particular component of
the ecosystem which he or she studies. Many of their principal points have been included in the Strategy at the
appropriate places, but here they are speaking in their own words.

A brief summary of their main recommendations:
MODELING:
HABITAT RESTORATION:
MONITORING:
RESEARCH:
Each community needs to be included in water quality models. They should also be included
in models which track energy or carbon transfers.

Vascular plants, whether submerged (SAV)  or  emergent (wetlands), are important to the
habitats of all communities. Preservation of existing acreage should be given high priority.

Maintaining existing monitoring programs and the inclusion of ecologically valuable species
previously excluded should have a high priority. Analyses should be carried out which will
bring out community features having to do with function, such as the proportion of predators,
proportion of large and small individuals, or respiration.

Studies  need to clarify  linkages between water quality  and biological communities, and
between the plants, herbivores and predators of each community.
The most important message that these scientists wanted to give is to look at the Chesapeake Bay ecosystem as a large
and complex community, where each species is  linked to others and to the habitat.
                                                                                                         25

-------

-------
 THE
                                                                                                    Jon H.
                                                                          The University of Maryland System
                                                           Center for Environmental and  Estuarine Studies
                                                                             Chesapeake Biological Laboratory
                                                                                           Solomons, Maryland

                                                  ABSTRACT

The microbial loop is composed of a large group of microscopic organisms ranging  from bacteria to tiny animals  (bactivors)
which feed upon them. The loop functions in Chesapeake Bay as a major catalyst of nutrient and carbon cycling and may also
form the base of a food web analogous to the more usual phytoplankton-zooplankton  system. Two metabolic groups  within the
loop, aerobic heterotrophic bacteria which inhabit the Bay's water column and anaerobic sulfate-reducing bacteria residing chiefly
in Bay sediments, are responsible for anoxic and hypoxic conditions in Bay deep waters. An unusually large amount of carbon
and energy in the Bay now seems to be dissipated by the microbial loop rather than transferred up the  food web. The magnitude
of carbon flow and oxygen-consumption processes attributable to the microbial loop may be decreased by nutrient reduction
(supply side) or species replenishment (demand side) strategies. Augmentation of filter-feeding communities (e.g., oysters) and
submerged aquatic vegetation may be particularly important to the latter strategy. Monitoring efforts need to include assessment
of microbial loop biomass and metabolism. Further research is necessary to explore ways to decrease the influence of the micro-
bial loop in the Bay's ecosystem.
                  INTRODUCTION

To many people, mention of the terms "microbial loop" or
"bacteria in the Bay" generates the vision of the Chesapeake
as a large reservoir of disease-causing microorganisms. In
reality, however, most aquatic microorganisms do not cause
disease, but rather  are important components  of aquatic
ecosystems within  which they  function  to recycle organic
materials and  may, as well, form the base of a microbial
food  web analogous  to  the more classic phytoplankton-
zooplankton-higher animal scheme. A key feature of this
microbial food web is that it is composed  of a  greater
number of energy  transfers than the phytoplankton-zoo-
plankton scheme. Thus,  its efficiency is  necessarily lower
and  a smaller  fraction of production ultimately reaches
higher,  economically important trophic levels  (e.g.,  fish,
crustaceans, oysters).

The "microbial loop" is comprised of two major groups of
microscopic organisms,  bacteria  (prokaryotes)  and  tiny
animals (eukaryotes) which feed upon the bacteria. These
animals,   termed   bactivors,   comprise  part  of   the
microzooplankton. Ciliates, in  particular, are known bacti-
vors, but the importance and magnitude of energy transfer
from  bacteria  to   microzooplankton  and  from  micro-
zooplankton to mesozooplankton  is poorly understood for
natural aquatic environments (Brownlee  and Jacobs 1987).
Currently available data for the Bay suggest that the bacteria
are a  carbon  sink  (Ducklow  et al.  1986,  Malone  and
Ducklow 1990), but the potential in the Bay for substantial
energy transfer  from bacteria to higher organisms deserves
further attention (see RECOMMENDATIONS).
            REPRESENTATIVE SPECIES

Given the paucity of information on bactivory in aquatic
environments  in general and  in  the  Chesapeake Bay  in
particular, much of the remainder of this discussion focuses
on bacteria. The concept of bacterial indicator species has
proved highly successful over  a long period of time for
assessing pollution (e.g., coliform counts as indicators  of
fecal contamination). With regard to ecosystems, however,
the concept of indicator species has much less value for bac-
teria. It appears to be more useful in terms of describing
the state of the ecosystem to divide the bacteria into meta-
bolic groups which delineate the roles they play in geochem-
ical cycling and carbon flow (Table 1). Of particular impor-
tance  to the  Bay ecosystem are  those  metabolic groups
which  play quantitatively significant  roles  in  oxygen
consumption,  namely  the aerobic  heterotrophic group and
the sulfate-reducing microbial community.

                   IMPORTANCE

Two  key  bacterially  catalyzed  processes  drive  oxygen
depletion in the mesohaline region of the Bay (Tuttle et al.
1987a). Oxygen consumption may be linked directly  to the
oxidation of organic carbon (CH2O) by aerobic heterotro-
phic bacteria (Table 1)  residing in the water column (termed
pelagic bacteria or bacterioplankton)  and in  oxygen-con-
taining  surficial sediments. This  process (equation  1) is
necessarily  restricted  to  the aerated portion of the water
column during anoxic events.

         (CH2O) + O2 —> CO2  +  H2O  (Eq. 1)
                                                                                                                27

-------
Table 1. Simplified listing of some major bacterially catalyzed processes which occur in the Chesapeake Bay.
Process
Aerobic Decomposition
Sulfate Reduction
Sulfate Oxidation
(Sulfide Oxidizers)
Nitrification
Denitrifi cation
Methanogenesis
Energy
Source
Organic C
Organic C
Sulfide
Ammonia
Nitrite
Organic C
Hydrogen,
Simple Organic C
Carbon
Utilized
Organic
Organic
Inorganic
Inorganic
Organic
Inorganic
Electron
Acceptor
Oxygen
Sulfate
Oxygen
Oxygen
Nitrate,
Nitrite
Carbon
Dioxide
Primary Bacterial
Metabolic Group
Aerobic Heterotrophs
Anaerobic Heterotrophs
(Sulfate Reducers)
Aerobic Autotrpphs
Aerobic Autotrophs
(Nitrifiers)
Anaerobic Heterotrophs
(Denitrifiers)
Anaerobic Autotrophs
(Methanogens)
The second process which contributes to oxygen consump-
tion involves the  cycling  of sulfur.  The key  chemical
reactions are  depicted by equations 2 and 3.

         2(CH20) + SO/~-*H2S + 2HC03"(Eq.2)

           H2S + 2O2 -»•  SO/ + 2H+ (Eq. 3)

Equation 2 represents the oxidation of organic carbon by
sulfate-reducmg bacteria, anaerobic microorganisms which
use sulfate  rather  than  oxygen  as  a  terminal  electron
acceptor (Table  1). Sulfide  (H2S),  the  product of sulfate
reduction, reacts  with oxygen directly (equation  3) or  in-
directly via reactions involving iron or other metals. Sulfide
oxidation reactions occur abiologically  as well as by the
metabolism of sulfide-oxidizing bacteria (Table 1). Sulfide
is  produced  mainly  in the  sediments,  even when  Bay
bottom waters are anoxic  (Turtle  el al.  1987a, 1987B).
Oxygen consumption by sulfide  oxidation  (equation 3)
occurs  in  surficial  sediments or  at the sediment-water
interface when bottom waters contain dissolved oxygen and
within the water  column in the region  of the pycnocline
when  bottom waters are anoxic.

Detailed description of processes affecting the establishment
and maintenance of hypoxic and anoxic conditions can be
found elsewhere (Tuttle et al. 1987a, 1987b), but it is impor-
tant to consider here the  magnitude and  timing of the
bacterially catalyzed processes depicted  in equations  1 and
2.  Sustained  bacterioplankton abundances in  the mid-Bay
during the  warmer  months  of the year are very  high,
averaging about  1010  cells  per  liter  (Malone  et  al.   1986;
Tuttle  et al.  1987a; Jonas and  Tuttle  1990). These  large
standing crops of bacteria consume oxygen at a rate of 1-1.5
mg O2 per liter per day (Tuttle et al. 1987a).  Sediment
sulfate reduction (sulfide  production) rates in the mid and
lower Bay are among the  highest found in marine environ-
ments  (Tuttle el al.  1987a; Roden and  Tuttle, in revision)
and rates in the upper  Bay are  substantial, even at condi-
tions of limiting sulfate concentrations (Roden and Turtle,
in review). Recent modeling exercises indicate that bacterio-
plankton oxygen consumption  is most important in the
spring, whereas sediment sulfide production and subsequent
sulfide  oxidation becomes dominant  during the summer
(Roden and Turtle,  in press; Kemp et al., in prep.). These
findings contradict earlier studies which attributed oxygen
consuming processes chiefly to the water column (Taft et til.
1980) or sediments only (Officer et al. 1984).

Although a variety of other microbial groups are undoubt-
edly also important with regard to geochemical processes
occurring in the Bay (Table  1),  the sheer magnitude of or-
ganic carbon  flow needed to support the metabolism  of
aerobic heterotrophic bacteria and sulfate-reducers as well as
their demonstrated role as key players in oxygen consuming
processes indicate that these groups should be targeted. The
carbon  flow question in particular has critical implications
for the  Bay ecosystem, even if nutrient  reduction strategies
to  limit  phytoplankton   prove  sufficient  to   eventually
decrease the extent and duration of anoxia. In the mid-Bay,
for example,  pelagic bacteria alone can account  for a  very
large portion of primary net production (Table 2). Addition
to this of the roughly equal amount of carbon required  to
support sediment microbial processes, sulfate reduction  in
 28

-------
Table 2. Percentage of phytoplankton net production metabolized
by pelagic bacteria in the mesohaline Chesapeake Bay. Estimates
taken from Baird and Ulanowicz (1989).
                                     Season
                        Spring  Summer    Fall     Winter
 % of Phytoplankton
   Production
25
        50
                 30
                         28
particular (Roden 1990), gives rise to an ecosystem unduly
dominated by carbon and energy flow through the microbi-
al loop.

  STATUS/FUNCTION/COMMUNITY STRUCTURE
                    INDICATORS

Status
Abundance is a good  indicator  of the  status of  pelagic
bacteria, particularly if their biomass (which can be calculat-
ed  from  abundance estimates) is compared  to  that of
phytoplankton  0onas and Turtle  1990; Gilmour et al., in
press). A  decreasing ratio of bacterioplankton biomass to
phytoplankton  biomass would signal  ecosystem  improve-
ment in that it implies decreased carbon flow from primary
production through the microbial loop.

The status of the sediment community of sulfate-reducing
bacteria is more difficult to  assess because both culturing
and direct count  enumeration   methods  for  them  are
inadequate and genetic probe methods  (e.g.,  Devereux et al,
1989)  for reliably   estimating their  biomass  in natural
environments have  not  yet been developed.  Because their
function  (i.e., sulfide production) is  of  greatest interest,
measurements of their metabolism by  35S procedures (e.g.,
Jorgensen  1978; Roden and Tuttle, in  press) is  also an
appropriate estimate of their  status. These  methods  are,
however,  labor intensive, relatively expensive, and  require
substantial technical expertise. A more reasonable approach
would be to  monitor water column sulfide concentrations
during  anoxic  events. Roden  and Tuttle (in  press)  have
demonrated  that  sulfide flux  from  mid-Bay  sediments
approximates 35S-estimated sulfate reduction  rates when the
sediments are overlain by anoxic bottom water. Therefore,
decreases  in sulfide concentrations in anoxic waters should
be indicative of decreased sediment sulfate reduction rates.

Function
The function of microbial communities is typically assessed
by  measuring some feature of their metabolism or their
productivity.   Production   by   aerobic    heterotrophic
bacterioplankton  is  commonly estimated  from 3H-methyl
thymidine incorporation measurements (e.g., Malone et al.
1986; Ducklow et al. 1986; Tuttle et al. 1987a; Jonas et al.
1988; Jonas and Tuttle 1990;  Gilmour et al., in press).
Community function can be characterized in more detail by
using radiotracer  methods to assess  the metabolism of
specific  carbon sources such as amino acids, carbohydrates,
fatty acids, etc. (Jonas et al. 1988; Bell 1990; Gilmour et al,
in press).  The function of sulfate-reducing microbial com-
munities is assessed by measuring the  reduction of 35S-sul-
fate (see above).

Community Structure
The  structure of natural microbial communities has  been
determined  by culturing samples in a variety of specific
media  (e.g.,  plate counts,  most  probable number  tech-
niques). These  methods are very tedious and often lead to
underestimation of the microorganisms present. It has be-
come more popular to infer community structure from me-
tabolism measurements (see Function), but in this case, we
gain information only about  metabolic groups within the
community.  Species   and genera cannot  be  identified.
Genetic probe methods with which we could test for codes
of specific processes, genera, or species hold the promise of
permitting us  to  rapidly  and accurately assess microbial
community structure. However,  it is  likely to be several
years before these methods are at  the stage of development
where they can be reliably used with environmental samples.

  QUALITATIVE AND QUANTITATIVE TARGETS

In order to set targets for the microbial loop component of
the Bay's  ecosystem, we  must  first address the question of
whether the situation  now existing in  the Bay represents  a
"healthy" or "unhealthy" ecosystem. For  reasons discussed
above (see IMPORTANCE), it is clear that a large portion of
primary production in the mid-Bay is currently dissipated
by microbial  processes which are directly responsible for
oxygen  consumption  and thereby for the establishment and
maintenance of  hypoxia and anoxia.  From a pragmatic
point of view, one  can  argue  that  if  this  represents  a
"healthy" situation, management  efforts  to improve water
quality  and production of harvestable living resources will
prove difficult at best.

Two questions  regarding ecosystem structure seem germane
to the Bay ecosystem  health problem. These are:

1. Is the current Bay ecosystem fundamentally different
from that which occurred in the past, i.e.,  was the microbial
loop as important a player in the past as  it is now?

2. Is the current Bay ecosystem fundamentally different
from that of other marine or estuarine environments less
impacted  by anthropogenic inputs?

Both these questions are difficult to answer directly because
experimental   methods  to  adequately  assess   microbial
biomass,  production,  and metabolism on a large system
                                                                                                                   29

-------
scale have existed  for only two decades  or less.  However,
recent  evidence  from examination of mid-Bay sediments
(Cooper and Brush 1991) indicates increased sulfur cycling.
since  colonial times.  Analysis of historical (mid-1930s to
mid-1980s) mid-Bay deep water dissolved oxygen levels in
the vicinity of Cove Point shows statistically significant de-
creased dissolved oxygen concentrations over successive time
spans of about a decade (Cargo et al. 1986). Both these lines
of evidence are consistent with increased microbial metabo-
lism.

The second  question is equally difficult to answer because
complete  ecosystem  evaluation  data   for  marine  and
estuarine systems are  relatively rare. Nevertheless, network
analysis of carbon flow through several marine ecosystems
indicates that the Chesapeake  is a stressed environment,
characterized by an ecosystem having shorter cycles  and
more  rapid  carbon turnover than less  impacted environ-
ments  (Baird et al. 1991). These features are consistent with
ecosystems  in  which  the  microbial   loop  plays  a
disproportionately large  role. Thus, such data  as are now
available all point to microbial loop communities in the
Bay which process a  disproportionately large quantity of
available organic  carbon and  which have a detrimental
effect on water quality.

In terms of establishing  qualitative or quantitative targets
for reducing the impact of  microbial  communities,  one
must ask: is  it in fact possible to manage microbial communities
on the scale of the Chesapeake, Bay ecosystem? Given the likely
condition that the magnitude of microbial biomass, produc-
tion, and metabolism in the Bay is ultimately related to the
amount of  internal organic  carbon  production (autoch-
thonous phytoplankton primary production) and external
inputs (allochthonous carbon from terrestrial sources),  it is
theoretically feasible to control microbial  communities by:

1. Decreasing autochthonous  production through nutrient
reduction  strategies and  allochthonous carbon  inputs  by
effective waste treatment and  land management practices
(bottom-up or supply side control), and by

2. Redirecting a portion of autochthonous production  and
allochthonous carbon through compartments of the eco-
system other than the microbial loop (top-down or demand
side control).

The first of these strategies, already in practice and aimed
primarily at decreasing phytoplankton production, would
be expected to decrease  microbial loop  community pro-
duction with a concurrent decrease in oxygen consumption
and improved water quality. However, there is no reason to
expect  that the proportion of carbon processed by microbial
communities would be altered (i.e.,  even less  production
would  be available for transfer to higher  trophic levels).
The second strategy, relying on higher trophic level consum-
ers (e.g., oysters) whose community could be directly man-
aged, would permit a greater proportion of production to
be "captured" by species  more desirable than microorgan-
isms. Modeling studies comparing filtering rates of historic
and current oyster  abundances (Newell 1988; Newell et al.
1989), model scenarios depicting increased  oyster densities
in  rafted  aquaculture  or on  oyster  bars (Gerritsen et al.
1989), and  field  measurements assessing the current Bay
trophic state (Tuttle  et al.  1987a)  suggest  that increasing
oyster densities should  positively impact Bay water quality
and revitalize the nearly  extinct Chesapeake Bay shellfish
industry. Indeed, field studies on pelagic microbial processes
and organic carbon at an oyster aquaculture facility demon-
strate  significant removal of  phytoplankton,  microbially
labile paniculate organic carbon, and pelagic bacteria within
the oyster raft area compared to waters outside the raft area
(Jonas and  Tuttle,  in  press).  The  field results  have been
supported qualitatively by a quasi-equilibrium, mass action
model  of  the  exchanges  transpiring in the  mid-Bay
(Ulanowicz  and Tuttle, in press). The  predictions of this
model, the findings of the aquaculture  field study, and the
hypothesis that submerged aquatic vegetation (SAV) baffling
effects could enhance settling of suspended material and
phytoplankton to the benthos (R. Newell and W. Dennison,
personal communication), give rise to the following simpli-
fied ecosystem result of increasing SAV and oyster densities:

         >   SAV   &   OYSTERS    =   <
         PHYTOPLANKTON   =  <  PELAGIC
         BACTERIA  = < O2 DEMAND = > O2
         CONCENTRATIONS = > FISH

Potential  problems arising  from this "bioremediation"
scheme are that increasing oyster densities could stimulate
phytoplankton production via remineralization of nutrients
from  oyster  biodeposits (e.g.,  Jordan   1987)   and the
biodeposits  themselves  could increase sediment oxygen
demand  (Gerritsen et  al. 1989). However, increased cell-
specific phytoplankton production has not been  observed
in  oyster aquaculture  field studies (Jonas  and Tuttle, in
press;  Ulanowicz  and  Tuttle,  in press)  and preliminary
results of a current study of microbial processes (including
sulfate reduction) and oxygen demand in sediments beneath
oyster aquaculture  rafts suggest  that increases  in oxygen
demand and microbial  metabolism are  relatively small and
of short duration (Tuttle and Jonas, unpublished). It is thus
reasonable to propose that increasing oyster densities (and
perhaps SAV as well) represents a potentially useful method
to augment  the strategy of mitigating eutrophication in the
Bay through reduction of nutrient inputs (Ulanowicz and
Tuttle, in press).

Unfortunately, our  knowledge of the microbial loop as  it
now functions in the Bay environment is insufficient to set
30

-------
quantitative targets for reducing its influence. It is possible
to predict with some certainty, however, that management
strategies  which  decrease  phytoplankton  production  or
partially interrupt carbon flow directly from phytoplankton
to bacteria will likely result in decreased microbial abun-
dances  and  activities,  particularly  of pelagic  microbial
communities.

               RECOMMENDATIONS

Monitoring
1. Include enumerations of bacterioplankton in the Chesa-
peake Bay Monitoring Program.

Bacterioplankton abundance  is directly  proportional  to
water column oxygen consumption rate (Tuttle et al. 1987a;
1987b). Therefore, it  is  possible to assess both the state of
lower trophic levels  (by comparison with phytoplankton
biomass estimated  from chlorophyll)  and  follow  oxygen
consumption with  one,  relatively  simple  measurement.
Direct epifluorescent counting of microorganisms is less
labor-intensive  than making  measurements  of  oxygen
consumption and, after the initial purchase  of appropriate
microscopic   equipment,    is   cheaper.   Decreased
bacterioplankton abundance  will signal improving eco-
system health in the Bay, particularly if the ratio of bacteri-
al biomass: phytoplankton biomass  also decreases.

2. Monitor  H2S in the Bay and tributaries  during anoxic
events.

Although sulfide  is  being measured  in the monitoring
program,  detailed (e.g., 1-2 m intervals)  profiles are not
made to my knowledge. As discussed above, sulfide loading
(integrated sulfide concentrations) to  the water column is an
approximate indicator of sediment sulfate reduction  rates.
Decreased  sulfide loading (as  well as  areal extent and
duration of anoxia) to the water column, particularly from
year to year, will  be indicative of improving  sediment
conditions and because  sulfide is toxic  to animal and  plant
life, an  indicator of improving habitat.

Research
1. Accelerate and expand studies aimed at quantifying how
increased oyster stocks and SAV can  improve water quality
and increase the health  of the ecosystem.

Bioremediation strategies based on increased oyster densities
have been evaluated so far only in open creek systems where
mass balances cannot be obtained. Laboratory or mesocosm
studies are needed to quantify how  the ecosystem compo-
nents change under  controlled conditions.  Field  studies
should  include combined water  column  and  sediment
assessments  at aquaculture facilities  and at oyster  bars.
2. Continue  research on oyster diseases and the develop-
ment of disease resistant oysters.

Bioremediation procedures will be relatively ineffective if
substantial portions of the augmented communities become
infected with MSX or Dermo.

3. Estimate the contribution of microbial loop production
to higher  organisms.

This is a key gap in our knowledge of how the Bay ecosys-
tem  operates.  If there are .important  Bay  species  which
depend upon this path  of carbon flow, desirable compo-
nents of the ecosystem could be decreased by clean up stra-
tegies which decrease bacterial biomass and production.

4. Determine what factor(s), if any, control microbial loop
biomass and  production.

Conventional  wisdom  suggests  that organic  carbon  is
probably  limiting the  heterotrophic bacterial community,
but neither this, nutrients  (N and P), or predation have
been investigated as possible limiting factors. Results from
this research could permit us to select appropriate methods
and  set attainable targets  for  those methods  aimed  at
controlling biomass and production of the microbial loop.

5. Assess the importance of the microbial loop in the Upper
and Lower Bay and in the tributaries.

Most of the information  on the role of the microbial loop
in the Chesapeake has been  gained  from  studies on  the
mesohaline mainstem. We know little about the situation
existing in the Lower,  more  saline mainstem or the less
saline Upper  Bay. Likewise, apart from the Patuxent, we
know virtually nothing  about the  tributaries. The role  of
allochthonous  carbon  in fueling bacterioplankton produc-
tion and  microbial sediment processes needs to  be deter-
mined.  A recent study has found  that,  at times, bacterio-
plankton  production  in the upper reaches of the Patuxent
exceeds   primary   production,   presumably    due   to
allochthonous carbon input (Gilmour el al., in press). If this
is characteristic of the upper reaches of other tributaries and
the Bay itself, the elevated importance of the microbial loop
could have a  profound influence on the status and function
of the ecosystem existing there.

6. Estimate   the  response  of  the   microbial   loop   to
dinoflagellate blooms.

Sellner (e.g., Sellner and  Olson 1985,  Sellner and Brownlee
1990) has aptly  pointed out  that dinoflagellate blooms,
although relatively short in duration, could  provide substan-
                                                                                                                    31

-------
tial organic carbon to the Bay and its tributaries.  Prelim-
inary  evidence  (Tuttle,  unpublished)  indicates   major
increases in bacterioplankton biomass, production,  oxygen
consumption,  and nutrient  concentration associated with
these blooms. The  influence of these  large but transient
carbon inputs on the  Bay's ecosystem is largely unknown.

Modeling
1. Include bacterioplankton in water quality models.

2. Expand  models by including major sediment bacterial
processes (e.g., sulfur  cycling,  methanogenesis, iron reduc-
tion, nitrogen cycling).

Management
1, Improved efforts to control exploitation and replenish
predator stocks should be encouraged.

As discussed above, there are reasons  to believe the top-
down control  could influence the microbial loop so as to
produce a "healthier"  ecosystem.

Habitat
Decreases in biomass of and carbon flow through microbial
loop communities are most  likely  to improve habitats  by
decreasing  organic carbon loss, oxygen consumption, and
the extent and duration of anoxia.
                    REFERENCES

Baird,  D., J.M. McGlade and  R.E.  Ulanowicz.  1991. The
comparative ecology of six marine ecosystems. Philosophical
Transactions of the Royal Society of London 333: 15-29.

Baird, D. and R.E. Ulanowicz. 1989.  The seasonal dynamics
of the  Chesapeake Bay ecosystem. Ecological Monographs
59: 329-364.

Bell, J.T. 1990. Carbon  flow through  bacterioplankton in
the mesohaline Chesapeake Bay. M.S. Thesis. University of
Maryland College Park.  126 pp.

Brownlee, C.L and F. Jacobs. 1987.  Mesozooplankton and
microzooplankton in the Chesapeake Bay. Chapter 12, pp.
217-269,  In:  Majumdar, S.K., L.W. Hall,  Jr.  and H.M.
Austin (eds.), Contaminant problems and management of
living Chesapeake Bay resources. Pennsylvania Academy of
Sciences.

Cargo, D.G., J.H.  Tuttle and  R.B.  Jonas.  1986. The low
dissolved oxygen situation in the Chesapeake Bay: then and
now. Spring Meeting. AERS. Lewes,  DE.
Cooper,  S.R. and  G.S. Brush. 1991. Long-term history of
Chesapeake Bay anoxia. Science 254: 992-995.

Devereux, R., M. Delany, F. Widdal and D.A. Stahl. 1989.
Natural  relationships  among sulfate-reducing eubacteria.
Journal of Bacteriology 171: 6689-6695.

Ducklow, H.W., D.A.  Purdie, P.J.  LeB. Williams  and J.M.
Davies. 1986. Bacterioplankton:  a sink for carbon  in  a
coastal marine plankton  community. Science 232: 865-876.

Gerritsen, J., A. Ranasinghe and  A.   F. Holland.  1989.
Comparison of three strategies to improve water quality in
the Maryland portion  of Chesapeake Bay. Report to Mary-
land Department of Natural Resources, Appendix C, 20 pp.

Gilmour, C.C., G.S. Riedel and D. Kizer. Dynamics of the
microbial food  web in the Patuxent River:  heterotrophic
bacterioplankton. New Perspectives on  the Chesapeake Bay.
CRC. (in press)

Jonas,  R.B., J.H. Tuttle,  D.L Stoner and H.W. Ducklow.
1988. Dual-label radioisotope method  for simultaneously
measuring bacterial production and metabolism in natural
waters. Applied Environmental Microbiology 54: 791-798.

Jonas,  R.B. and J.H.  Tuttle.  1990.  Bacterioplankton and
organic carbon  dynamics in the  lower mesohaline  Chesa-
peake Bay. Applied  Environmental Microbiology 56: 747-
757.

Jonas,  R.B. and J.H.  Tuttle.  Improving Chesapeake Bay
water quality: influence  of rafted  oyster aquaculture on
microbial processes and  organic carbon. New Perspectives
on the Chesapeake Bay. CRC. (in press)

Jordan,  SJ.  1987.  Sedimentation  and  remineralization
associated  with biodeposition  by  the American  oyster
Crassostrea virginica (Gmelin). Ph.D. dissertation. University
of Maryland, College Park.

Jorgensen, B.B.  1978.  A comparison of methods for the
quantification  of  bacterial sulfate  reduction in  coastal
marine sediments.  I. Measurement with radiotracer  tech-
nique.  Geomicrobiology  1: 11-27.

Kemp, W.M.,  P.A.  Sampow, J.  Garber, J.  Tuttle, W.T.
Randall and W.R. Boynton. Seasonal depletion of oxygen
from bottom waters of Chesapeake Bay: Roles of benthic
and planktonic respiration and physical exchange processes.
(in preparation)

Malone, T.C. and H.W. Ducklow. 1990. Microbial biomass
in the  coastal plume  of Chesapeake Bay: phytoplankton-
32

-------
bacterioplankton  relationships.  Limnology  and  Ocean-
ography 35: 296-312.

Malone, T.C., W.M. Kemp, H.W. Ducklow, W.R. Boynton,
J.H. Tuttle and R.B. Jonas. 1986.  Lateral variation in the
production  and  fate  of  phytoplankton  in  a  partially
stratified estuary. Marine Ecology  Progress Series 32: 149-
160.

Newell, R.I.E.  1988. Ecological changes in Chesapeake Bay:
are they the result of overharvesting the American oyster,
Crassostrea  virginica! In:  Understanding  the  Estuary: Ad-
vances in Chesapeake Bay Research. CRC Publication 129.

Newell, R.I.E., J.  Gerritsen and  A. R Holland.  1989. The
importance of existing and  historical bivalve populations in
removing phytoplankton biomass from Chesapeake Bay. In:
Abstract of the Tenth Biennial International  Estuarine Re-
search Conference.

Officer, C.B., R.B. Biggs, J.L Taft,  L.E. Cronin, M.A. Tyler
and W.R. Boynton.  1984.  Chesapeake Bay anoxia: origin,
development and significance. Science 223:22-27.

Roden, E.E, 1990. Sulfate  reduction and  sulfur cycling in
Chesapeake Bay sediments.  Ph.D. dissertation. University of
Maryland College Park. 256 pp.

Roden, E.E. and J.H. Tuttle. Sulfide  release from estuarine
sediments underlying anoxic bottom water. Limnology and
Oceanography (in press).

Roden, E.E. and J.H. Tuttle. Inorganic sulfur cycling in mid
and  lower  Chesapeake  Bay  sediments.  Marine  Ecology
Progress Series (in revision).
Roden, E.E. and J.H. Tuttle.  Inorganic sulfur turnover in
oligohaline estuarine  sediments. Limnology  and Oceano-
graphy (in review).
Sellner,  K.G. and M.M. Olson. 1985. Copepod grazing in
red tides of Chesapeake Bay.  pp.  245-250, In: Anderson,
D.M., A.W. White and D.G.  Baden  (eds.), Toxic  dino-
flagellates. Elsevier, New York.
Sellner, K.G.  and  D.C. Brownlee.  1990.  Dinoflagellate-
microzooplankton interactions in Chesapeake Bay. pp. 221-
226, In: Graneli,  E., B. Sundstron,  L  Edler and  D.M.
Anderson (eds.), Toxic marine phytoplankton. Elsevier, New
York.
Taft, J.L, W.R. Taylor, E.D. Hartwig and R. Loftus. 1980.
Seasonal oxygen depletion in Chesapeake Bay. Estuaries 3:
242-247.
Tuttle, J.H., R.B. Jonas and  T.C.  Malone. 1987a. Origin,
development and significance of Chesapeake Bay anoxia. In:
Majumdar,  S.J., LW.  Hall,  Jr. and  H.M. Austin  (eds.),
Contaminant  problems and  management of living Chesa-
peake Bay resources. Pennsylvania  Academy of Sciences  31
pp.
Tuttle, J.H., T.C. Malone, R.B. Jonas,  H.W. Ducklow and
D.G. Cargo. 1987b. Nutrient-dissolved  oxygen dynamics in
Chesapeake Bay: the roles of  phytoplankton and micro-
heterotrophs under  summer conditions,  1985. U.S. EPA,
CBP/TRS 3/87. 158  pp.
                                                                                                                   33

-------

-------

                                                                                                     Kevin Sellner
                                                                                  Academy of Natural Sciences
                                                                                 Estuarine Research Laboratory
                                                                                              Benedict, Maryland
                  INTRODUCTION

Phytoplankton are  microscopic  plants found throughout
aquatic systems and form the base of the food web in most
of  these  systems. Their  production,  accumulation  and
subsequent  decomposition  govern  higher  trophic  level
productivities as well as nutrient and dissolved oxygen (DO)
concentrations  in the Chesapeake  Bay and its tributaries.
The on-going  Chesapeake Bay Water Quality Monitoring
Program for Maryland and Virginia, funded through the
respective states and  the U.S. EPA, is largely committed to
establishing potential linkages  between  these  primary
producers and  nutrient loads and concentrations in the
systems. The basic premise is that the reduction of nutrient
loads  to  the system will reduce phytoplankton production
which, in turn,  will lead to lower biological oxygen demand
(BOD) in  the  system  and  higher DO  concentrations in
bottom waters of stratified Chesapeake Bay.

On another level, phytoplankton are also strongly linked to
production of higher trophic levels  in the system, including
commercially valuable fish and shellfish stocks. The transfer
of  energy  from  these  planktonic  autotrophs  governs
production in  the highest trophic levels through a complex
food  web  from phytoplankton  to  suspension feeding
herbivores to small and larger carnivores. These linkages are
dependent on size and "taste" of the phytoplankton as well
as system characteristics  that  provide either favorable or
restricted habitats for potential grazers and predators in the
system. The efficiency of this linkage may  then control
production of our living resources  in our system.

The smallest phytoplankton are the picophytoplankton,
hereafter referred to as picoplankton, averaging 1-2 \im and
ranging  from   0.2-2 um.  Nanophytoplankton, or  nano-
plankton, range from 2-20 um, while larger cells are includ-
ed  in  the microplankton (20-200 um) and mesoplankton
(>200 (Lim). Previous estimates of the relative contributions
of these size classes of phytoplankton to the total communi-
ty indicate major contributions in the nanophytoplankton,
primarily as centric diatoms and  microflagellates. As shown
in most recent studies, picoplankton generally contribute on
the order of 10-20% of total pigment  and biomass  pro-
duction but have contributed up to 50% (Lacouture et al.
1991, Malone et al. 1991, Sellner et a!., in prep., a). Larger
cells  in  the microplankton may  dominate  the  phyto-
plankton  community  early  in  the  spring  bloom (e.g.,
Cerataulina pelagica, Rhizosoknia spp.) and in some summer
dinoflagellate   blooms  (e.g.,  Gymnodinium,  Ceratium).
Nanoplankton  and smaller macroplankton are preferred
food items for  the largest  planktonic  herbivores, which in
turn are the primary prey for larval and some forage fish in
the system.

Dissolved oxygen concentrations in mesohaline and poly-
haline bottom waters of Chesapeake Bay are a function of
stratification intensity  derived  through   spring  runoff,
nutrient loads to the head of the Bay early in the spring,
and the magnitude of the spring phytoplankton bloom. The
magnitude of the spring bloom  is dependent  on nutrient
levels entering from the Susquehanna River early in the year
(see Malone et al. 1988) with the size  of the bloom tightly
coupled to the delivery of nitrogen, phosphorus and silicon
from January-March. If runoff is reduced during this period
or is delayed until after this period (as in 1989), the spring
bloom will be  smaller with  lower  total  phytoplankton
accumulation in the system (Sellner et al., in prep., b). Most
of  this  spring  diatom production  settles  directly  to the
bottom of  the  Bay forming a  large reservoir of  labile
organic matter  that fuels high  oxygen demand,  largely
bacterial,  in late  May-early June causing a precipitous
decline in DO and hypoxic to anoxic conditions in bottom
waters of the deep trough of Chesapeake Bay from June-
September. The gradient in salinity across the pycnocline, a
function of freshwater runoff, determines the ease to which
bottom waters are re-aerated during the continuously low
DO summer period in the Bay as well as the  ease with
which regenerated  nutrients  from  decomposing  spring
bloom production mixes into surface waters fueling summer
phytoplankton  productivity (Malone  1992, Malone et al.
1986, 1988).

Quantifying the importance of phytoplankton to produc-
tion of the higher trophic  levels has been more difficult to
assess in Chesapeake Bay.  In general,  zooplankton are not
thought to be limited by a scarcity of phytoplankton food

-------
in Chesapeake Bay, with a few exceptions (e.g., Eurytemora
affinis in the Patuxent River; Heinle and Flemer 1975). Our
estimates suggest that zooplankton remove on  the order of
20-30% of annual mesohaline phytoplankton production
(K. Sellner and F. Jacobs, unpubl. data) with the highest de-
mand  in February-March when phytoplankton  standing
crops and production in surface waters are low and August-
September when the copepod Acartia tonsa dominates the
zooplankton. This seasonal heterogeneity in zooplankton
herbivory and reworking of phytoplankton is also support-
ed in carbon and pigment deposition rates for mesohaline
Chesapeake Bay (Boynton et al 1991).

The absence of food limitation for the zooplankton suggests
that zooplankton densities might be controlled  through top-
down rather than bottom-up mechanisms. Therefore,  much
of  the  Bay's phytoplankton  production probably  cycles
through pico-microheterotrophs  of the "microbial loop."
This processing mechanism, i.e., degradation in the microbi-
al loop, is a less efficient pathway for the transfer of energy
from the phytoplankton to higher trophic levels  resulting
in lower production  in our commercially valuable resource
stocks  than  would   be  expected  from   the  classic
phytoplankton-copepod-fish food web.

        REPRESENTATIVE GROUPS IN THE
                 PHYTOPLANKTON

There  are certainly  specific groups  of phytoplankton  in
Chesapeake Bay and its tributaries that could be categorized
as indicators of "healthy"  or "unhealthy" conditions in the
system; there are even some species that could be considered
representative of "good" or "bad" conditions. However, use
of one species as an  index of the system's balance without
considering accompanying changes in water quality and the
plankton is to be avoided. A responding system includes the
interactions of many species as well as species-water quality
interactions; therefore, many species and the  surrounding
particulate and dissolved pools must be examined before the
"health" of the system can be ascertained.

Phytoplankton  groups  or  characteristics that might  be
employed with other system parameters to indicate "health"
include:
3) Relative contributions of specific phyla in a system, as
diatoms/cyanobacteria or diatoms/total phytoplankton.

However,  these indices must be compared to other charac-
teristics of the system collected over long time periods that
include vertical stratification, short- and long-term meteorol-
ogy (e.g.,  wind- or storm  induced mixing), zooplankton
stocks present (e.g., micro- vs. mesozooplankton dominance)
as well  as stocks of benthic (oysters) or nektonic (men-
haden) herbivores  in a region.  These factors all influence
phytoplankton composition on  short time scales that if not
examined  over a long period could lead to erroneous  con-
clusions  about  phytoplankton  responses  to  a  managed
Chesapeake Bay.

The importance of these factors  in defining system "health"
can be seen with the following examples. In the Potomac
River,  nutrient  loads have been  declining over the  last
decade.  Accompanying  this decline has been  the  virtual
disappearance  of bloom-forming cyanobacteria in tidal-fresh
portions of the upper river (Fig. 1). This decline in cyano-
bacteria with  a corresponding increase  in  the ratio  of
eucaryote  biomass/total phytoplankton biomass has  also
been   paralleled   by  a  decline   in  the  biomass   of
microzooplanktonic herbivores  in  the system suggestive of
a reduced importance of the microbial loop in the river.
         1985
                 1986
1987    1988
    YEAR
                                                 1990
         til^IZl 2 YR P LOAD           CYAN C/10
                     —  ANN C FIX
         	MESOZP C       •»   *   MZP C
1) Abundance of "nuisance" species such as bloom-forming
colonial cyanobacteria (e.g., Microcystisaemginosa.,Agmendlum
or Apbanizomenon) or dinoflagellates  (e.g., Gymnodinium,
Gyrodinium, Ceratium);

2) Relative contributions  of net phytoplankton (> 10 Jim),
picoplankton   (<3  um)   or  eucaryotes   to  the  total
phytoplankton community; and
Figure 1. Plankton responses to declining phosphorus loads in the
surface mixed layer of the tidal-fresh Potomac River, 1985-1990.
Loads represent average 2 year loads for 1984-1985, 1985-1986,
1986-1987, 1987-1988, 1988-1989 and 1989-1990. The vertical
axis  represents phosphorus loads (kg per  day)  and carbon
responses (g per  square meter), respectively.  CYAN C/10 is the
carbon produced  by bloom-forming cyanophytes  divided by 10,
ANN C FIX is the annual productivity, MZP C and MESOZP  C
represent biomass of the microzooplankton and mesozooplankton,
respectively.
 36

-------
Thus, for the Potomac, reduced  nutrient inputs appear  to
reduce  the  importance  of non-nutritious  cyanobacteria
which  in turn reduces the contribution of the smallest
herbivores,  the  microzooplankton,  and potentially the
microbial loop. This reduction in the high oxygen-demand-
ing microbial  loop, in turn, might be accompanied by an
increase  in  larger  phytoplankton,  larger zooplanktonic
herbivores and more efficient transfer  of phytoplankton
production to commercially-valuable fish stocks through the
classic  food  web.

Top-down control of phytoplankton has also been suggested
as a factor to be considered in Bay management strategies.
The elimination of most of the oyster stocks in the Bay has
been suggested as a prime reason  for  the  emergence  of
picoplankton as a dominant member of the phytoplankton
community  (Newell et al. 1988) with a concomitant increase
in the  importance of the "microbial loop" in the system.
This loop, in turn, supports low bottom DO concentrations
over most of the Bay's deep trough. One would expect the
picoplankton/total  phytoplankton ratio to increase as the
oyster  stock declined. One proposed means to (1)  reduce
phytoplankton stocks  decomposing  in  bottom  sediments
leading to low DO and poor habitat and (2) remove of a
large portion of the energy entering the microbial loop  as
picoplankton production would be to suspend bivalves over
large portions of the surface (mixed layer) of the Bay and
its  tributaries. These suspension  feeders could incorporate
excessively high phytoplankton production into harvestable
tissue,  effectively reducing bottom  water BOD  as well  as
water column oxygen  demand  characteristic of the active
microbial loop of the watershed.

The reduction  in nutrient loads, particularly  silicon,  in
delayed spring runoff or in drought can be accompanied by
unusually low diatom biomass in the spring in Chesapeake
Bay (Wagoner et al.  1990; Conley and Malone 1992; Sellner
et al. in prep., b). In 1989, peak  runoff was delayed in the
spring  until  May. This delay resulted in much lower diatom
accumulations in the spring and reduced diatom loading  to
the bottom. As a result, DO decline in bottom waters of the
deep trough was  also  delayed. Relative to normal  runoff
years, the duration  of low bottom water DO was reduced
(R. Magnien, unpublished data). Part of the explanation for
reduced diatom production was attributable to unusually
low silicon concentrations in mesohaline Chesapeake Bay
during the optimum temperature period for diatom growth.
This control of diatom accumulation in the region through
silicon limitation implies  some potential for  control  of
phytoplankton   production  through   manipulation   of
nutrient loads in point- and, to  a lesser degree, non-point
source  contributions. As Officer and Ryther (1980) have
suggested, silicon additions to sewage  treatment effluents
might effectively select for more nutritious diatoms possibly
leading to more effective energy transfer to the top predato-
ry fish as well as formerly dominant oyster populations.

Changing water quality (high nutrients or elevated  metal
levels)  can also cause  a  shift in  size of the  dominant
phytoplankton resulting  in  elevated  production of the
smallest phytoplankton (see Sanders et al. 1981) and  their
planktonic  herbivores  (e.g.,  heterotrophic  flagellates),
reduced production in the larger  copepods and top preda-
tors, the fish  and a selection  for ctenophores and medusae
in some  systems  (Greve and Parsons  1977,  Landry 1977,
Parsons 1979). Shifts in community structure such as  these
are easily followed in controlled mesocosms  but definitive
examples  in  complex  natural systems are  less obvious.
However, shifts in size distributions of the phytoplankton,
as in biomass of the <10 jam fraction to the total communi-
ty  biomass,  could  provide  an  indication  of  potential
problems for the Bay  if examined over a sufficiently long
time period.

Linkages between phytoplankton and top predators are even
more difficult to  establish.  In a  recent review of  three
separate ichthyoplankton data bases for the Bay and two of
its  tributaries, Sellner  and Brownlee (unpubl. data) noted
strong correlations between striped bass and white perch
larvae densities and zooplankton biomass  when copepods
exceeded  50 per liter  or, alternatively,  when  >44 Jim non-
tintinnid microzooplankton, exceeded 940 per liter. In addi-
tion, coincident high fish  larvae densities and zooplankton
biomass were  also accompanied  by correspondingly high
juvenile indices  for  these  periods  for the respective fish
species (Buchanan  1992). High zooplankton densities in the
spring in these systems are coincident with  abundant net
phytoplankton biomass  and  the  absence  of "nuisance
species. The  larger and  apparently  more  palatable  and
oxidizable phytoplankton community supports successful
zooplankton production and hence  fish larvae development
in these systems.

                      SUMMARY

Phytoplankton in Chesapeake  Bay  are  the  primary
integrators of ambient water  quality and  as  such, provide
ideal "indicators" of system health. The abundance of small
picoplankton in the Bay and the overwhelming importance
of bacterial oxygen demand during the decomposition of
settling phytoplankton implies that the microbial  loop is
the primary shunt for phytoplankton production  in  the
system. This cycling of energy and nutrients in the smallest
autotrophs and heterotrophs results  in lower energy transfer
to the highest  trophic levels and might partially explain (at
some minor fraction of fishing pressure) some of the lower
fish and shellfish stocks in the region. In addition, nuisance
algae, such as  cyanobacteria blooms in the Potomac River
                                                                                                                   37

-------
in the last  several decades and  red or mahogany tides
resulting  from  dinoflagellate  blooms,  favor  microbial
processes rather than the classic phytoplankton-copepod-fish
food webs, further reducing the transfer of primary produc-
tivity of the phytoplankton to our commercially valuable
fish and  shellfish stocks.

Monitoring  distributions  of these algae as well as total
contributions  of  larger net  phytoplankton will provide
information on the size spectra of the primary  producers
present and  therefore the dominant patterns of energy and
nutrient cycling in the system: large contributions from the
smallest algae  relative to larger eucaryotes implies limited
production in higher trophic  levels relative to production
when large phytoplankton predominate.

Future management strategies should include large compo-
nents for assessing phytoplankton size distributions simulta-
neously  with   water  quality, vertical  stratification  and
distributions of potential herbivores in the system. We can
effectively assess  the "health" of Chesapeake  Bay and its
tributaries only by assessing all of these parameters simulta-
neously;  no  one character will provide distinct and  defini-
tive indication of Bay recovery.

                    REFERENCES

Boynton, W.R., W.M.  Kemp, J.M. Barnes, L.L  Matteson,
J.L  Watts,  S.  Stammerjohn, D.A.  Jasinski  and  P.M.
Rohland.  1991.  Chesapeake Bay water quality monitoring
program:  Ecosystems Processes  component.  Level  I  data
report f 8. Part 1: Interpretive report. [UMCEES] CBL Ref.
No. 91-110,  Solomons, MD. 118 pp.

Buchanan, C.  1992. Chesapeake Bay zooplankton monitor-
ing.  Interstate Commission on the Potomac River Basin,
Rockville, MD.  17 pp.

Conley,  D.J.  and T.C. Malone.  1992.  Annual cycle of
dissolved silicate in Chesapeake Bay: Implications for the
production  and  fate  of phytoplankton biomass. Marine
Ecology-Progress Series 81: 121-128.

Greve, W. and T.R. Parsons.  1977. Photosynthesis and fish
production: Hypothetical  effects  of climatic  change and
pollution. Helgo. wiss. Meeresunters. 30: 666-672.

Heinle, D.R. and D.A. Flemer. 1975. Carbon requirements
of a population of the estuarine copepod Eurytemora affinis.
Marine Biology 31: 235-247.

Lacouture, R.V., B.B. Wagoner, E. Nealley, K.G. Sellner and
R. Summers. 1991. Dynamics of the microbial food web in
the Patuxent River: Autotrophic picoplankton.  Pages 297-
318, in: J.A, Mihursky and A. Chancy (eds.), New perspec-
tives  in  the  Chesapeake system.  Chesapeake  Research
Consortium Publication 137, Solomons, MD.

Landry, M.R.  1977. A review of the important concepts in
the trophic organization of pelagic ecosystems. Helgo. wiss.
Meeresunters.  30: 8-17.

Malone, T.C.  1992.  Effect of water column processes  on
dissolved oxygen, nutrients, phytoplankton and zooplank-
ton. Pages  61-112,  in:  D.E.  Smith,  M.  Leffler and  G.
Mackiernan (eds.), Oxygen dynamics in the Chesapeake Bay.
Maryland Sea  Grant, College Park, MD.

Malone, T.C.,  W.M.  Kemp, H.W. Ducklow, W.R. Boynton,
J.H. Tuttle and  R.B. Jonas. 1986. Lateral variation in the
production  and fate  of phytoplankton in  a  partially
stratified  estuary. Marine Ecology-Progress Series 32: 149-
160.

Malone, T.C., L.H. Crocker, S.E. Pike and B.W. Wendler.
1988.  Influences  of river  flow  on  the  dynamics  of
phytoplankton production in a partially stratified estuary.
Marine Ecology-Progress Series 48: 235-249.

Malone, T.C., H.W. Ducklow,  S.E. Pike  and E.R. Peek.
1991. Picoplankton  carbon flux in Chesapeake  Bay.  Abst.
and presentation,  llth  International  Estuary Research
Federation Meeting, San  Francisco,  CA,  10-14  November
1991.

Newell, R.I.E.  1988. Ecological changes in Chesapeake Bay:
Are they the result of overharvesting the  American oyster,
Crassostrea virginica? Pages 536-546 In: M.P. Lynch and E.G.
Krome  (eds.), Understanding  the  estuary:  Advances  in
Chesapeake  Bay research. CRC Publ.  129  &  US  EPA
CBP/TRS 24/88, Solomons, MD.

Officer, C.B.  and J.H. Ryther. 1980. The possible impor-
tance of silicon in marine eutrophication. Marine Ecology-
Progress Series 3: 83-91.

Parsons, T.R. 1979.  Some ecological,  experimental  and
evolutionary  aspects  of the upwelling ecosystem.  South
African Journal  of Science 75: 536-540.

Sanders, J.G., J.H. Ryther and J.H. Batchelder. 1981. Effects
of copper, chlorine  and  thermal addition on the species
composition of marine phytoplankton. Journal of Experi-
mental  Marine Biology and Ecology 49: 81-102.

Sellner, K.G.,  R.V. Lacouture and B.B. Wagoner, (in prep.,
a). Autotrophic picoplankton in the Patuxent River estuary.
 38

-------
Seilner, K.G., R.E. Magnien, B.B. Wagoner, F. Jacobs, W.R.         Wagoner,  B.B.  and   K.G.   Sellner.   1990.  Seasonal
Boynton and J.G. Brownlee. (in prep, b). The 1989 spring         phytoplankton assemblages in Chesapeake Bay. Abstract and
bloom in Chesapeake  Bay: Where  have all the diatoms •        presentation,  ASLO,  College  of  William   and   Mary,
gone?                                                         Williamsburg, VA, 10-15 June 1990.
                                                                                                                39

-------

-------

                                                                                              Harold G. Marshall
                                                                             Department of Biological  Sciences
                                                                                      Old Dominion University
                                                                                                 Norfolk,  Virginia
                  INTRODUCTION

The  phytoplankton community in the lower Chesapeake
Bay is a composite of neritic species entering at the mouth
of the Bay, freshwater populations transported from  the
various river systems,  and resident estuarine species within
the Bay.  They include at least nine taxonomic categories
that  are seasonally dominated by diatoms, cryptomonads,
dino-flagellates  and cyanobacteria (Marshall   1980,  1991;
Marshall  and  Alden  1990a).  In  addition,   autotrophic
picoplankters and a  variety of microflagellates  are  also
found  within  these waters  (Affronti 1990; Affronti and
Marshall  1990).   These  picoplankters  and   the  larger
phytoplankton communities are the producers for microbial
and  metazoan populations.  Due to this  relationship, and
subsequent zooplankton  linkages  to  higher trophic levels,
the Chesapeake Bay is a plankton driven  system.

            REPRESENTATIVE SPECIES

Early studies of phytoplankton composition in Chesapeake
Bay include Wolfe et at. (1926) and Patten et al. (1964), with
the  importance of nanoplankton  in these   waters  first
emphasized by McCarthy et al. (1974) and Van Valkenburg
and  Flemer (1974). More recently,  Marshall  (1991) and
Marshall  and  Alden  (1990a) discussed  results from  an
extensive five year data base that included the composition,
spatial and temporal patterns of phytoplankton in the  lower
Chesapeake Bay,  and  their  relationships to water quality
variables.  This  lower  Bay population included over 480
phytoplankton species. Annually they went through six to
eight successional stages, where specific floral  assemblages
had seasonal maxima, during spring, summer and fall. The
total phytoplankton can also be divided into broader "cold"
and  "warm" water floral  groups, that  occur during winter-
spring and summer-fall months. These various maxima and
their  assemblages  are influenced by changes  in salinity,
temperature,  nutrients   and   turbidity   levels, and  vary
annually  in  their   onset,  magnitude  and  duration.
Phytoplankton in the  local tributaries also have spatial and
temporal  patterns of development,  with a transition of
species assemblages occurring downstream, as tidal  fresh
water algae are replaced  by estuarine flora (Marshall and
Alden 1990b).
The characteristic species associated with the different saline
concentrations in the lower Bay and its tributaries are given
in Table 1.  These phytoplankters, and a  variety of other
background   species,   will  vary   in   their  abundances
throughout the year.


                INDICATOR SPECIES
The  phytoplankton  of the  lower  Chesapeake  Bay  is
characterized by a seasonally dynamic and diverse group of
species. Their growth is not excessive, and they  are appar-
ently not over-grazed, with  the Bay plume distinct in  its
composition  and concentrations of cells in comparison to
neritic waters (Marshall  1982, 1991). Due to their brief life
span,  phytoplankton cells  will respond  within hours  to
environmental  changes  and new species  assemblages can
develop within  days in response to  changing water quality
conditions. These changes often favor the growth of certain
phytoplankton  species,  and   may  even  promote   the
development of blooms resulting in  more stress to the local
biota. At present, blooms in the lower Bay are not extensive,
frequent,  or  long  lasting (Marshall  1989).   They  are
associated with dinoflagellate growth, and mostly confined
to the local river systems, where  they are more common.
Blooms that  occur in the lower Bay system are monitored
by our laboratory to follow their occurrence and associated
environmental conditions.
In contrast to bloom formation, more lasting assemblages
are correlated to the succession of species which takes place
during eutrophication stages. Population shifts in the major
floral categories indicate  stress associated  with eutrophic
changes.  Examples would  include a change from a system
dominated by diatoms to one dominated by cyanobacteria,
or  the  change from  nano-  and  micro-phytoplankton
components to a picoplankton-dominated habitat.


                LONG TERM TRENDS
Applying a series of statistical steps to a five year data set,
Marshall and Alden (1991) evaluated long term trends of
                                                                                                                  41

-------
 Table 1. Dominant phytoplankters associated with various salinity regions in the lower Chesapeake Bay and its tributaries.
TIDAL FRESHWATER
Asterionella formosa
Chroococcus limneticus
Cyclotella meneghiniana
Cyclotella striata
Melosira distans
Melosira granulata
Merismopedia tenuissima
Microcystis aeruginosa
Scenedesmus spp.
Skeletonema potamos

OL1GOHALINE
Cryptomonas spp.
Cyclotella striata
Melosira distans
Melosira granulata
Microcystis aeruginosa
Skeletonema potamos





MESOHALINE
Asterionella glacia/is
Cerataulina pelagica
Cryptomonas spp.
Cyclotella caspia
Heterocapsa triquetra
Katodinium rotundatum
Leptocylindrus minimus
Prorocentrum minimum
Rhizosolenia fragilissima
Skeletonema costatum

POLYHAUME
Asterionella glacialis
Ceratium lineatum
Cerataulina pelagica
Chaetoceros spp.
Leptocylindrus minimus
Leptocylindrus danicus
Prorocentrum micans
Rhizosolenia alata
Rhizosolenia stolterfothii
Skeletonema costatum
Thalassionema nitzschioides
phytoplankton abundance and biomass composition within
the lower Chesapeake Bay and several tributaries in relation
to water quality and other variables. This analysis indicated
a slight, but significant trend of increased abundance and
biomass for  phytoplankton in  Bay  waters  above the
pycnocline, which was most pronounced  in summer. This
increase was  associated  with  higher  concentrations  of
dinoflagellates, small  centric diatoms  and  several   other
phytoflagellates.  In contrast, a modest,  but significant
decline occurred below the pycnocline for both abundance
and biomass. This pattern was most distinct during winter.
These  patterns were associated with a significant seasonal
trend of increased species diversity above and below the
water column.  These results  support conclusions made by
Marshall and  Lacouture  (1986) that  changes have  been
taking  place in the composition of Bay phytoplankton.
When examined over short time  intervals, these changes can
be expected to  be subtle, but it is evident  from our studies
that this community  is  sensitive and  responsive to the
gradual water quality changes occurring in the Bay.  These
annual  statistical  analyses  of  phytoplankton  and  water
quality data will be continued, to provide  specific informa-
tion relevant to evaluating the  health status of  the  lower
Chesapeake Bay.

               RECOMMENDATIONS

Monitoring
1. Continue monitoring phytoplankton  populations in the
lower Chesapeake Bay. Phytoplankton populations represent
the major  food producer  and  oxygen  source  within the
Chesapeake  Bay.  Knowledge  of the  composition   and
concentrations  of the  phytoplankton  community  will
provide direct  information regarding local stress and the
regional health status of the Bay.  Changes in phytoplankton
composition will act as one of the first indicators of stress
in  the  ecosystem.  A  long term monitoring program  is
necessary to obtain adequate data to distinguish true trends
from population changes that may be attributed to normal
and/or  annual ranges of development.

2. Greater  emphasis  should  be  placed  on reporting the
incidence and location of  blooms by toxin and non-toxin
producing  species. More  information  on  the  increasing
concentrations of phytoplankton now occurring  will  be
needed  for future management decisions. The Old Domin-
ion University Phytoplankton Laboratory will continue to
be the depository for information on bloom events in the
lower Chesapeake Bay.

3. Phytoplankton monitoring should continue to  include
the autotrophic picoplankton community. The balance, or
changes  that occur between  these populations will  aid in
evaluating the health status of the lower Bay, or in specific
areas  of the system.

Research Activities
1. Greater understanding is  needed on trophic relationships
between  the  flora and  fauna within the microbial loop.
Although picoplankton are recognized as  major producers
within the  Bay  system, little  is known about  the fate of
these cells and their linkages to metazoan populations. Such
relationships would become more significant if a  shift to a
more picoplankton dominated system develops.

2. The  Elizabeth River is  a unique habitat under stress.
More data is needed to understand  local associations of
picoplankton, phytoplankton,  and zooplankton  and  the
impact the degraded water  quality has on these couplings.
42

-------
                      SUMMARY

The lower Chesapeake Bay contains a diverse assemblage of
phytoplankters and a representative autotrophic picoplank-
ton  population.  Specific phytoplankton  assemblages  are
found in the eastern, western and north central sections of
the lower Bay, and these assemblages pass through a series
of six to  eight successional stages a year. These temporal
changes are associated with major periods of growth and a
transition in species composition.

These studies also indicate that the phytoplankton contains
a variety of potentially harmful species that may produce
extensive blooms and degrade water quality. For instance,
Marshall  and Soucek  (1993) reported that five different
dinoflagellates produced extensive blooms in the lower Bay
from July through September 1992.  The largest bloom was
produced by Cochlodinium  beterolobatum and persisted  for
four weeks over an area of 215 km2 in the Bay. In addition,
the first Chesapeake Bay  record of the toxin-producing
dinoflagellate Pfiesteria piscimorte has been reported by Alan
Lewitus of the University of Maryland (Greer 1993) from
Jenkins  Creek off the Choptank River. These events indicate
that the Bay  and its fisheries  are vulnerable to harmful
phytoplankton species.

In conclusion, Marshall and Alden (1993) updated their
previous  phytoplankton trend studies  in the lower Bay
using a six-year database (1985-1991). They found significant
seasonal trends  of reduced cell concentrations  across  all
their stations. These trends  mainly developed during spring
and  were associated with reduced diatom abundance and
lowered phosphorus levels. Future monitoring of the Bay
phytoplankton populations will provide information on: 1)
whether these trends will prevail, or are short-lived, 2) the
response of present  phytoplankton assemblages to changes
in existing water quality conditions, 3) what are the linkages
to  environmental  factors  and  biota  that influence  the
growth of the various phytoplankton categories, and  4) how
these findings will be useful to management in reducing the
occurrence and impact of bloom events.

                    REFERENCES

Affronti, L 1990. Seasonal and diel patterns of abundance
and productivity of phototrophic picoplankton in the lower
Chesapeake  Bay.   PhD.  dissertation.   Old  Dominion
University, Norfolk, VA. 141 pp.

Affronti,   L.  and  H.G.  Marshall.  1990.  Picoplankton
dynamics  in  the lower Chesapeake Bay. Association of
Southeastern Biologists Bulletin 37(2):  69.

Greer, J. 1993. Alien in our midst? Phantom algae suspected
in Bay. Maryland  Marine Notes. ll(2):l-3. Maryland Sea
Grant  College,  University  of  Maryland,  College  Park,
Maryland.

Marshall,  H.G. 1982. The composition of phytoplankton
within the Chesapeake Bay  plume and adjacent waters of
the Virginia  coast,  U.S.A.  Estuarine, Coastal and  Shelf
Science 15: 29-43.

Marshall,  H.G.  1989. An appraisal  of bloom producing
phytoplankton in  the Chesapeake Bay. Final Report. VEE
No. 85-17, Old Dominion University Research Foundation,
Norfolk. 28 pp.

Marshall, H.G. 1991. Preliminary results of phytoplankton
composition,  abundance  and  distribution  in the  lower
Chesapeake Bay monitoring program. Special Reports. Old
Dominion University Research  Foundation, Norfolk.  117
pp.

Marshall,   H.G. and  R.W.  Alden.  1990a.  Spatial  and
temporal  diatom  assemblages  and  other phytoplankton
within the lower Chesapeake Bay. In: H. Simola (ed.) Pro-
ceedings of the 10th  International Diatom  Symposium.
Koeltz Scientific Books, Koenigstein, pp. 311-322.

Marshall,  H.G. and  R.W. Alden. 1990b. A comparison of
phytoplankton assemblages and environmental relationships
in three estuarine rivers of  the lower Chesapeake Bay.
Estuaries 13: 287-300.

Marshall,  H.G. and R.W.  Alden.  1991. Phytoplankton
abundance,  composition and  trends  within the  lower
Chesapeake Bay. In: J. Mihursky and A. Chancy (eds.), New
Perspectives in the  Chesapeake  System:  A  research  and
management   partnership.  Proceedings  of  a  Conference.
Chesapeake Research  Consortium  Publication  No.   17,
Baltimore,  pp. 517-522.

Marshall, H.G. and R.W. Alden. 1993. Long  term  trends in
the lower  Chesapeake Bay: Phytoplankton. Association of
Southeastern Biologists Bulletin  40(2): 138-139.

Marshall, H.G. and R. Lacouture. 1986. Seasonal patterns of
growth and composition of phytoplankton in the lower
Chesapeake Bay and vicinity. Estuarine, Coastal and Shelf
Science 23: 115-130.

Marshall,  H.G. and K. Soucek. 1993.  Red tide bloom in the
lower  Chesapeake  Bay:  September  1992. Association of
Southeastern Biologists Bulletin 40(2): 140.

McCarthy, J.,  W. Taylor  and M.  Loftus. 1974. Significance
of nanoplankton   in  the Chesapeake Bay  estuary  and
problems associated with the measurement of nanoplankton
productivity. Marine Biology 24: 7-16.
                                                                                                                  43

-------
Van Valkenburg, S. and D. Flemer.  1974. The distribution
and productivity of nanoplankton in a temperate estuarine
area. Estuarine and Coastal Marine Science 2: 311-322.
Wolfe, J., B. Cunningham, N. Wilkerson and J. Barnes.
1926. An investigation of the microplankton of Chesapeake
Bay. Journal of the Elisha Mitchell Scientific Society 42: 25-
54.
44

-------

Ray S. Birdsong
Department of Biological Sciences
Old Dominion University
Norfolk, Virginia
                                          Buchanan
                           Interstate Commission
                     on the Potomac River Basin
                        6110 Executive Boulevard
                              Rockville, Maryland
                  INTRODUCTION

The zooplankton community sampled by the Chesapeake
Bay Program is a principal component  of the  estuarine
ecosystem. Zooplankton form an essential link in the food
web and provide the bulk of the forage prey for most larval
and juvenile fishes as well as  many other estuarine organ-
isms.  Although we have a conceptual framework for  the
Chesapeake Bay ecosystem, details of the linkages, fluxes,
sinks and shunts involving major functional groups such as
zooplankton are for the most part poorly understood. It is
apparent, despite this rudimentary understanding, that  a
disproportionately large amount of algal carbon and energy
in the bay presently seems to enter the microbial  loop (see
"The Microbial Loop" chapter). Primary consumers in the
zooplankton as well  as the benthos and other groups are
not passing  large enough  quantities of  algal   primary
production up the food web, and excessive amounts of algal
materials are being shunted to the microbial loop. Possible
reasons  why critical  trophic  linkages are decoupling  are
poorly understood but may include  1) an increase in  the
smaller   zooplankton  (microzooplankton)  favored  by
eutrophy and  less preferred  as food  for  larval  fish,  2)
excessive cropping of larger zooplankton (mesozooplankton)
by zooplankton predators, and 3)  inhibited growth and
reproduction  caused  by toxics, hypoxia  or  poor  water
quality. Models, long-term data  sets, and ecosystem indica-
tors can be powerful tools in furthering our understanding
of the complex Chesapeake Bay ecosystem and in eventually
managing man's impacts on the bay. These three kinds of
tools require individual blends of monitoring data and re-
search results in order to generate  information useful to
management agencies. Construction of working models of
the Chesapeake Bay ecosystem has received much attention.
The early  models are  heuristically valuable  but  much
remains to be done. Zooplankton variables, for example, are
not "turned on" in the current  Chesapeake Bay 3D Water
Quality Model, and functions describing zooplankton need
to be  refined.  Long-term data sets are known  to provide
robust baselines from which to  measure system health and
progress towards restoration.  The value of these  types  of
data generally increases with time. Presently, we have  6 and
8 year zooplankton data sets  which are just beginning to
show significant trends that track changes in water quality.
Biological  indicators,   or  bioindicators,  of  ecosystem
"health"  are now widely recognized as  useful tools  with
which  to evaluate an ecosystem's ability to  function and
support diverse communities. Efforts are just now underway
to develop and implement zooplankton indicators of ecosys-
tem integrity for Chesapeake Bay.

     REPRESENTATIVE GROUPS AND THEIR
        IMPORTANCE IN THE ECOSYSTEM

The zooplankton are often divided into three size categories
which  somewhat   reflect  their  roles  in  ecosystems.
Microzooplankton (<.202 mm, includes rotifers, ciliate and
tintinnid  protozoans  and copepod nauplii) are closely
linked  to the microbial loop as consumers and are usually
not a predominant prey of the larger plankton and nekton
(free-swimming individuals such as fish).  Mesozooplankton
(>.202  mm, includes  copepods, cladocerans, ostracods,
barnacle larvae) are typically effective grazers/predators and
are frequently the predominant prey of larval fish and many
nekton. Macrozooplankton (includes  the jellyfish group,
amphipods, mysid shrimp, and insect and polychaete larvae)
are generally omnivores or predators, and are caught  by a
.500  mm mesh.

As a means of  assessing the health of the bay the zooplank-
ton community has much to recommend it. The communi-
ty is  temporally and  spatially  ubiquitous  and  may  be
sampled at any time and any place. The community is not
subject to direct human exploitation  and therefore interpre-
tation is not complicated by factors such as fishing mortali-
ty. The zooplankton community is biologically diverse with
some 400 taxa  commonly appearing in Chesapeake Bay and
therefore its constituent species display varying sensitivities
to a  wide variety  of  environmental  factors and   these
sensitivities often differ  from those of other monitored
communities.  The zooplankton community  has high tro-
phic connectivity within the bay ecosystem  and contains
many primary  and secondary consumers. The high level of
linkage provided by the community between the primary
producers and  the upper trophic levels renders it useful as
an integrator of the state of the system.
                                                                                                                45

-------
     INDICATORS OF ZOOPLANKTON STATUS,
    FUNCTION AND COMMUNITY STRUCTURE

 The Chesapeake Bay  has  been, and continues to be, the
 setting for  several  zooplankton research efforts.  A recent
 tendency of the numerous  universities,  institutions, and
 state and federal agency  laboratories  in the  bay area  to
 coordinate  research efforts and focus on ecosystem model-
 ling has encouraged research into zooplankton  functions in
 the bay ecosystem. Although life  histories of  many domi-
 nant species are fairly well documented, knowledge about
 habitat requirements and interrelationships among species,
 communities and functional groups is  still  fragmented.

 Zooplankton monitoring by management agencies has  been
 a  part of  the  comprehensive monitoring efforts in the
 Chesapeake Bay since  1984  (Maryland, District of Co-
 lumbia) and 1986 (Virginia). The purpose of these programs
 is  to  characterize  the  Bay communities,  to  establish a
 long-term baseline  for trend analyses and to identify zoo-
 plankton associations  with water quality and living resourc-
 es. The programs have focused  in early years on characteriz-
 ing the spatial and  seasonal  values and  patterns of the
 zooplankton community. It is the variations from normal
 patterns or  reference sites that provide information through
 which  the  integrity  of the  Bay's  existing zooplankton
 communities may be evaluated.

 At present, the Chesapeake Bay zooplankton  monitoring
 programs are using the following indicators of the health of
 the zooplankton community.  The interpretation of  these
 statistics must  be done against the backdrop of a long-term
 baseline that documents the annual cycle of abundance and
 takes  into  account the  effects of salinity  on  abundance,
 biomass and diversity,

 Biomass
 When corrected for salinity effects, low average biomass of
 the mesozooplankton  is correlated with poor water quality.
 Comparisons of mesozooplankton biomass have been made
 for Virginia sites,  excluding  bloom event (MOO mg per
 cubic  meter) to avoid  the distortion  provided by a few very
 large values. Plots of average values against salinity provided
 an easy way to  identify outlier sites. In Figure 1 the outliers
 SBE2, SBE5 and RET4.3 all experience frequent  to chroni-
 cally poor water quality.

Microzooplankton biomass is relatively high in freshwater
reaches with  high  nutrient  loads  and  decreases  when
nutrient loads  are reduced. A  recent reduction in annual
phosphorous loads in the Potomac  river appears to have
produced a  drop in cyanobacteria  biomass which has been
parallelled  by  a decline in microzooplankton  biomass,
suggesting that  these small consumers  are  responding to
lower food levels (Figure 2).
    33
    28
    23
    18
o
m
    13
           RET4.3
                     SBE5  SBE2
               10
                                            25
                                                    30
                        15        20
                        SALINITY (ppt)
Figure 1. Average zooplankton biomass excluding blooms (>100
mg/m3) v. salinity in Virginia meso- and polyhaline  water of the
Chesapeake Bay. Trend line excludes identified outlier sites.
          1985
         2YR
         PLOAD
                  1986    1987   1988    1989   1990
                        CYANC/10 •
                        MESOZP C
 ANN C FIX
••  MZPG
Figure 2. Plankton responses to declining phosphorus loads in the
surface mixed layer of the upper Potomac estuary, 1985-1990.
Loads represent average 2 year loads for 1984-1985, 1985-1986,
1986-1987,  1987-1988, 1988-1989 and 1989-1990. The vertical
axis  represents phosphorus loads (kg per day) and carbon
responses (g per  square meter), respectively. CYAN C/10  is the
carbon produced  by bloom-forming cyanophytes divided by 10,
ANN C FIX is the  annual productivity, MZP C represents biomass
of the microzooplankton and mesozooplankton, respectively.
Abundance
As with biomass, zooplankton average abundance correlates
with water quality when corrected for salinity and bloom
events (Figure  3). The  advantage  of abundance  data over
biomass data is that the determination is not prevented by
heavy detrital  contamination  that  frequently  occurs  at
oligohaline sites. The disadvantage is that high abundances
of small species can distort the  relative importance of those
species  in the community.
 46

-------
Diversity
Between-site comparisons  in  Virginia  have not  revealed
noticeable decreases in absolute zooplankton diversity, even
at heavily impacted sites such as those in  the Elizabeth
River.  However, there are  shifts  in  species dominance as
rarer species become more  common with the reduction of
the normally dominant forms. Long-term trends in  diversity
at some  sites  have been noted and may  be an  effect of
changing water quality.
                   trations of nitrogen and phosphorus and the highest ratio
                   of microzooplankton to total  zooplankton. Lower ratios
                   and lower nutrient concentrations are found in the mid-Bay
                   and lower tributaries.
                   Other possible indicators of health of the Chesapeake Bay
                   zooplankton  community were  recently  identified  at  a
                   regional workshop (Buchanan 1992) and are presently being
                   developed. They include:
  20
  15
1
Q
§10
CO
O
                     t       .    I
                                       III
                                     TOXIC SITE
                    TOXIC SITE |
                     10      15      20
                         SALINITY (ppt)
25
                                                     30
Figure 3. Average summer zooplankton biomass at mainstem
station in the Virginia Chesapeake Bay.
 Unnatural variability in abundance and biomass
 High frequency of extreme abundance or biomass values is
 indicative of community instability and is associated with
 poor water quality. Virginia sites that experience chronically
 poor water  quality  display  different abundance  and/or
 biomass patterns  than those with  episodically poor water
 quality. Extreme values in mesohaline and polyhaline waters
 are presently defined for  mesozooplankton abundance as
 > 100,000 per cubic meter and < 1,000  per cubic meter, and
 for mesozooplankton biomass as >100 mg per cubic meter
 and <2 mg per cubic meter. These definitions were selected
 through  comparison  with values  from other  East Coast
 estuaries  and by comparing  Bay sites  that were apparently
 impacted with those that were not based on water quality
 characteristics. These definitions are subject to refinement
 and interpretation is subjective.
Ratios of specific taxonomic groups
A high ratio of microzooplankton  biomass to total  zoo-
plankton biomass  is frequently associated with poor water
quality  in  the  bay. This  supports  the hypothesis that as
eutrophication  occurs there is a shift to smaller,  micro-
zooplankton species in the  planktonic community. In the
Maryland mainstem, the upper Bay has the highest concen-
                   Ratios of various mesozooplankton taxa
                   A high  ratio of calanoid copepods to cyclopoid copepods
                   and  cladocerans seems  to  be associated  with  good water
                   quality in freshwater reaches of some tributaries.

                   Microzooplankton biomass in the deep trough
                   Microzooplankton biomass decreases in the deep trough of
                    the  mainstem after prolonged  hypoxia-anoxia. It may be
                    possible to use microzooplankton biomass as an indicator
                    of some critical change that occurs  as water quality deterio-
                    rates during summer hypoxia-anoxia.
                    Relative abundance of pollution tolerant and sensitive species
                    Specific species can be used as indicators of pollution events
                    or water quality.  Differences in physiology and ecology as
                    well as differences in physical location in the habitat cause
                    taxonomic groups to respond in diverse ways to a  water
                    quality condition. It has been shown that  some species in.
                    the zooplankton community show a sensitivity to certain
                    pollutants not seen in  other  monitored elements of the
                    biota, for example,  dissolved zinc,  copper and free cupric
                    ions  are  particularly toxic to  one  of the  Bay's dominant
                    copepods, Acartia tonsa (Sunda et al. 1990).
                    Presence of bypolrichs
                    One group  of sediment dwelling microzooplankters, the
                    hypotrich ciliates, are proving to be  excellent indicators of
                    low DO  conditions  in  the  system (p<.02). Anoxia or the
                    accumulation  of hydrogen  sulfide  in surficial sediments
                    appears to cause the  migration of these ciliates  into overly-
                    ing waters containing at least some oxygen. Future research
                    might determine the "memory" of these  events, and the
                    ciliates could be used as indicators of recent DO events.
                   Size structure
                   Compression  of the  size  frequency distribution  of the
                   mesozooplankton towards small sizes is a known indicator
                   of over-exploitation by forage fish.
                                                                                                                    47

-------
Fl
              Food limitation of larval fish
              An intensive analysis of three fish larvae databases obtained
              from J. Uphoff (MD DNR), E. Houde  and E. Rutherford
              (University of Maryland)  and R. C. Jones and D.  Kelso
              (George Mason University) and the Maryland zooplankton
              monitoring data showed that on those occasions when high
              densities of striped bass or white perch larvae were encoun-
              tered, mesozooplankton numbers exceeded  50-100 per liter
              or   excessively   high  microzooplankton  densities   were
              observed. The zooplankton monitoring data indicates that
              mesozooplankton numbers in the bay  and tributaries are
              frequently below the experimentally-determined minimum
              prey densities for normal larval growth  (Figure 4).
tuuu
500
£ 100
£ 75
z 50

< 15
i! 10
o
O 5
N
O
to
UJ
5
0-1








i







- - -:-•- ••-.- --•:->" MIfcllfiBlil*B'ilfflBtf":":"-"" "' •"•
.:"::•: :-: :•:-: Wil-IIIHlJIHrT-wM : : : : : : : :
.:' :?-lW


j
1







;¥x:-:-:.x-: ::-.::¥:-:-::-::: j


» <








\











\


^







8:88:
4

(












)




(








,:- - 1





f

















	 4



< 1




»
m CN crj -o fs CNCN *~. *~. cs
s g e |i || i se
.1"! ^ fe fi ^ ^ ^
                    JAMES
                            YORK
                                           x x       x
                                   RAPPA-
                                 HANNOCK POTOMAC  PATUXENT
                                                          CHOPTANK
UPPER
 BAY
              Figure 4. Spring abundance of mesozooplankton in spawning and
              larval  nursery areas of anadromous finflsh in  Chesapeake Bay
              (number per liter). Minimum  prey densities required for normal
              larval  growth  of  striped  bass  are   approximately   15-75
              mesozooplankton  per liter, depending upon species composition.
              The larvae typically feed first on microzooplankton and then switch
              to mesozooplankton as they grow. Median microzooplankton values
              (MD  tributaries)  usually  exceed  the required minimum prey
              densities for first-feeding larvae; this figure  indicates median
              mesozooplankton frequently do not exceed minimum prey densities
              for later stage larvae.

                Q  Median April-May-June densities
                 I Range of maximum and minimum during sampling period
                 1 (1985-1991  Maryland, 1985-1989 Virginia)
              Possible association of mesozooplankton  index  in  spring and
              juvenile Jinjish index in summer
              Further examination of the zooplankton monitoring data
              suggests the coincidence of high spring mesozooplankton
              abundances and high larval fish abundances can sometimes
              be associated with high juvenile indices later in the summer.
                     TRENDS


A major focus of the Chesapeake Bay Program zooplankton
monitoring  has  been the detection  of long-term  environ-
mental changes,  both natural and man induced (Birdsong
and Alden 1991). A scarcity of historical information  on
Chesapeake  Bay  zooplankton populations prevents direct
comparisons of existing conditions with those that prevailed
as recently as the 50's and 60's.  Zooplankton  monitoring is
only now of a  duration  that  exploration of the data in
search  of trends in  bioindicators  of health is  proving
fruitful. Some of the biomass, abundance and diversity data
have been analyzed with  a  series  of nonparametric trend
tests that included a seasonal interblock test based on the
Kendall Tau statistic (Hirsch et al. 1982), the aligned rank
test described by Sen (1968), the Van Belle and Hughes
chi-square test   (Van  Belle  and  Hughes  1984)  and the
seasonal Kendall slope estimator (Gilbert 1987). These tests
have been shown to be generally both powerful and robust
when tested  on representative data sets from the Chesapeake
Bay monitoring  program (Alden et al.  1990).

A synopsis of the trends is given below. Continued moni-
toring  and trend analyses is likely to  strengthen  some of
these apparent trends and  invalidate others. The correlation
of these apparent zooplankton  shifts  and  water quality
trends  should be viewed with circumspection.

In the polyhaline, Virginia  mainstem,  an increase in the
spring  abundance (February, March,  April) and in the
March and April diversity has  been  noted. These  increases
were  accompanied  by  tendencies  towards declines  ol
silicates,  nitrates, orthophosphates,  total  phosphorus  and
total nitrogen and increases  in  secchi depth and ammonia,
Also,  summer diversity 0uly,  August)  showed  an overall
decline that  was  accompanied by an overall increasing trend
in phytoplankton above  the  pycnocline and a tendency
towards decreasing nitrates. Winter values  displayed  an
overall decline  in abundance (November  and December
and  biomass  (November)  that  was  accompanied by  £
tendency toward declining nitrates.

In the  lower salinity mainstem, no discernable changes ir
the zooplankton community over time have been found fo:
the Maryland monitoring  program's   8  year time span
Mesozooplankton in the mesohaline  portion continue to bi
stressed by hypoxia and anoxia  in the summer and those ii
the upper, freshwater Bay are severely depressed by turbidity
nutrient enrichment and other  factors. Peaks  in the annua
patterns   of  mesozooplankton   and   microzooplanktoi
abundance  show considerable variability in timing  arw
intensity  from   year  to  year,  although the  dominan
copepods  Eurytemora  and  Acartia  show  strong, regula
seasonal signals.
             48

-------
Zooplankton seasonal signals  in the tributaries are often
shifted in time or rendered indistinct due to the consider-
able inter-annual and inter-tributary variation in river flow.
Despite the variability,  tributary trends  are evident. For
example, zooplankton populations in the  Potomac  and
Patuxent  are improving  as  nutrient  loads  decrease (see
above). Conversely, mesozooplankton  populations  in the
James   River  are  deteriorating  as   nutrients  increase.
Mesozooplankton diversity and biomass  have decreased as
secchi depth decreased and surface total phosphorus, surface
and bottom total  nitrogen, bottom ammonia and bottom
nitrate  increased  at up-river  stations. These trends  were
accompanied   by   an   overall  increasing  trend   in
phytoplankton biovolume (Marshall and Alden 1991) and,
at one  station (RET  5.2), an  increasing trend in benthic
biomass (Dauer  1991).
                 QUALITATIVE GOALS
It is only possible at this time to state qualitative goals for
the zooplankton community. Too little is still known about
zooplankton habitat requirements and the interrelationships
among species, communities and functional groups.

One obvious goal is a shift in  zooplankton community
structure such that dominance of the mesozooplankton over
the microzooplankton is strengthened, and algal carbon and
energy is  more likely to be  passed up the food web  rather
than to  the  microbial  loop. This  may occur as nutrient
loads - and eutrophication  - are reduced, however fishing
pressure  may also play a  role in accomplishing this goal.
Specifically,  overfishing  of gamefish  (usually  the top
predators) can allow excessive populations of forage fish to
become established. These in turn exert  severe  predation
pressure  on the mesozooplankton and reduce their ability
to regulate phytoplankton populations. Research into the
direct  and indirect effects of the absence of ecologically
important fishery species on lower trophic levels  should  be
encouraged  in ecologically-based  management  plans  for
these fisheries.

               RECOMMENDATIONS

1. The zooplankton monitoring program should continue
in some form similar to and compatible with that presently
being conducted.

2. The zooplankton monitoring data base remains largely
unexplored for water quality sensitive taxa and other  subtle
indices reflecting water quality.  The diverse  nature of the
zooplankton community present the strong likelihood that
sensitive bioindicators may be discovered. The  necessary
data for this exploration are available and costs would not
be great. This effort should be a primary research focus.

3. Directed  studies that link  biological shifts with water
quality in a  causal relationship should be conducted for all
monitored components of the zooplankton.

4.  Communication   between   managers  and  researchers
should be enhanced. In the past managers have often been
unfamiliar with the array and th£ interpretation of the bio-
logical data  available to them. Conversely, researchers need
to improve the form and presentation of data such that it
is accessible  and useful to environmental managers.

5. Enhance  use of zooplankton data in water quality and
ecosystem models.

                    REFERENCES

Alden, R.W. Ill, J.C. Seibel and C.M. Jones. 1990. Analysis
of the Chesapeake Bay Program monitoring design for de-
tecting  water  quality  and  living  resources  trends. Final
report to the Virginia Water Control Board. AMRL Techni-
cal  Report No. 747, 75 pp.

Birdsong, R.S. and R.W. Alden III.  1991. Long term trends
in the abundance and diversity of mesozooplankton of the
lower Chesapeake bay. New Perspectives in the Chesapeake
System:  Proceedings  of the  1990  Chesapeake  Research
Conference, Baltimore Maryland, December 1990. pp. 523-
526.

Buchanan, C. 1992. "Chesapeake Bay zooplankton monitor-
ing: report  on  a workshop  held  in  Easton, Maryland,
September 23-24, 1991." Prepared by the Interstate Commis-
sion  on  the  Potomac  River  Basin  and  the  Maryland
Department of the Environment, for the Living Resources
Subcommittee, Chesapeake Bay Program.)

Dauer,  D.M. 1991. Long-term  trends in the benthos of the
lower Chesapeake Bay, New Perspectives in the Chesapeake
System:  Proceedings  of  the  1990 Chesapeake  Research
Conference, Baltimore Maryland, December 1990, pp. 527-
536.

Gilbert, R.O.  1987. Statistical methods for environmental
pollution monitoring. Van  Nostrand Reinhold Co., New
York. 320 pp.


Hirsch, R.M., J.R. Slack and R.A. Smith. 1982. Techniques
of trend analysis for monthly water quality data. Water Re-
sources Research 18:  107-121.
                                                                                                                   49

-------
Marshall, H.G. and  R.W. Alden III. 1991. Phytoplankton
abundance,  composition and  trends within  the  lower
Chesapeake  Bay and three tributaries. New Perspectives in
the Chesapeake System: proceedings of the 1990 Chesapeake
Research Conference, Baltimore Maryland, December 1990,
pp. 517-522.
Sunda,  W.G.,  Tester, P.A.  and  S.A.  Huntsman.  1990.
Toxicity of trace metals  to Acartia tonsa,  in  the  Elizabeth
River and Southern Chesapeake Bay. Estuarine, Coastal and
Shelf Science 30: 207-221.
Sen, P.K..  1968. On a class of aligned rank order tests  in
two-way layouts. Annals of Mathematical Statistics 39: 1115-
1124.
Van Belle, G. and J. P. Hughes. 1984. Nonparametric tests
for trends in water quality. Water Resources Research 20(1):
127-136.
50

-------
FORAGE
                                                                                                       E.D.  Houde
                                                                              Chesapeake Biological Laboratory
                                                                                          University of Maryland
                                                                                             Solomons, Maryland
                  INTRODUCTION

Forage fishes are small fishes that  mature at a young age
and are abundant enough to be highly visible components
of the system. Their trophic status is variable. They may be
zooplanktivores,  phytoplanktivores, detritivores or omni-
vores. Reproductive modes are also  variable, but all (except
killifishes) have  pelagic larvae stages and, though few data
exist,  recruitment levels  probably  fluctuate significantly
from  year to year.

Forage fishes are included in a functional group of interme-
diate  consumers that potentially  affect  Chesapeake  Bay
water  quality through "top-down" trophic impacts. There is
no doubt that these small fishes are  important foods of top-
level piscivores in the Bay and fishery management ultimate-
ly must  consider how this forage  base sustains stocks of
striped bass,  weakfish, bluefish and  summer flounder.  The
so-called forage fishes are a diverse assemblage taxonomical-
ly and they occupy a variety of habitats. They also share the
intermediate consumer categorization in food webs  with
invertebrates such as gelatinous zooplankton,  which may
compete with the forage fishes for  limited food  resources
and channel consumed energy into trophic pathways  that
do not lead toward harvestable fish resources.

Although the role of forage fishes in  food chains that  fuel
the production  of  piscivores  is  intuitively  clear, their
importance   seldom   has  been  quantified.   Baird   and
Ulanowicz (1989) undertook a  network analysis  of the
Chesapeake   Bay ecosystem.  In  that analysis  only  bay
anchovy, and to a lesser extent menhaden, stand out among
fish species as obviously important  in an energetics sense  -
in terms of probable consumption,  storage and potential to
fuel  production of  larger fish. Results  of the network
analysis  may be  correct but it is possible that the better-
studied fish species have received disproportionate weight in
the analysis  and their  presumed  importance has been
overstated. The  level  of consumption and  production of
"forage  fishes"  such  as gobies, silversides, juvenile  river
herrings, killifishes,  etc. all may be  significant, especially
within the specific habitats  where they  live.  In a recent
analysis of Atlantic coastal and estuarine fish production,
Peters and Schaaf (1991) noted two major information gaps:
1) poor understanding of the role of detritus in food chains
and 2) a lack of data on the cost of forage fish production.

                    KEY SPECIES

There are key forage fishes that deserve special attention.
Bay anchovy and menhaden fall into this category. Roles of
other species are less clear but naked goby (Gobiosoma bosd)
and silversides (Menidia spp.) are important consumers and
producers,  as  are  killifishes  (Fundulus spp.,  Cyprinodon
variegatus) in their respective habitats. During the juvenile
stage, several  key Chesapeake Bay fishes  may serve  as
important  forage species. For  example, young-of-the-year
spot are abundant and productive, and are important forage
for piscivores in the Bay during this transition stage of their
life  history.

There are key invertebrate species that have at least "overlap-
ping functional roles" with forage fishes in the Bay ecosys-
tem. The gelatinous medusae and ctenophores are plankton
consumers  serving  that  role.  They not  only potentially
compete with  the fishes but may, together with the fishes,
cause a degree of top-down control over plankton  produc-
tivity and even water quality itself. Recent studies suggest
that consumption by the medusae and ctenophores general-
ly does  not  control  copepod production  in  the Bay
mainstem (J. Purcell, pers. comm.),  except under local and
temporally-restricted conditions  (Purcell and Nemazie,  in
press). Ingestion estimates for bay anchovy, although rather
preliminary,  indicate  that  immediately  after the  peak
recruitment period (September-October) in Chesapeake Bay
a significant  fraction  of the  standing  stock  and daily
production of copepods could be consumed (Vazquez 1989,
Klebasko 1991).

        IMPORTANCE TO THE ECOSYSTEM

A promising way to characterize functional groups and to
quantify their role in ecosystems is through analysis of food
web patterns. Food webs are complex. In aquatic ecosystems,
they may be especially complex because of shifts in trophic
status of individuals as they grow from  larval to adult stag-
es. However, recent progress in theory and  analysis indicates
that webs are "orderly and intelligible" and can be a useful
                                                                                                                   51

-------
tool to understand community dynamics (Pimm et al. 1991).
Properties of webs, the lengths of food chains, and the roles
of  component  species can  define important  ecosystem
properties  such  as  dominance  and  connectedness.  The
networking analysis of Baird and Ulanowicz (1989) was an
important  initial step  in determining functional groups in
the Chesapeake Bay. This approach and others that serve to
define trophic webs and properties, combined with bioener-
getics research, can lead to a proper evaluation of how well
the Bay is functioning. A workshop report on Bay Research
Needs (Houde 1987) essentially reached this conclusion five
years  ago.

Two general kinds of approaches are needed to quantify and
measure the properties of "functional groups." These could
be  termed  status  indicators  and  dynamic properties. Together
they may define the  "wellbeing"  of forage fish or,  more
generally,  functional groups in the Chesapeake  Bay. Status
measures   include  abundance,  biomass,   diversity,  and
distribution patterns. These measures can be converted into
indices, related to  environmental properties and subjected to
trend analyses. They are the heart of a monitoring program.
Dynamic measures  are more difficult to obtain but  they
define the properties of individual species and of functional
groups. Dynamic properties include measures of growth,
mortality,  production, and recruitment,  and also of the
variability  in these properties. These functional  properties,
when combined  with  food web analysis and bioenergetics
research/modeling, can lead  towards an understanding of
cause and effect relationships.

Several dynamic  properties of species and  groups can be
used  as status  indicators  if they are estimated  repeatedly,
and can be analyzed  to  determine temporal and spatial
variability. Some of these indicators will be non-dimensional
properties that serve well in comparative analyses. Examples
are assimilation and growth  efficiencies, or production to
biomass ratios (P/B) - opportunist species exhibit high P/B,
while equilibrium species display low P/B ratios. Trends in
these  properties  or distributional  patterns  for  individual
species or functional groups can help to define the "health"
of the Bay and its subsystems.

              MODELING STRATEGIES

While key species can be singled  out for  research,  their
interactions with  other species are complex and their effects
on  ecosystems difficult to evaluate. Models that elucidate
the functional role of intermediate consumers are needed to
learn  how they structure communities, promote stability or
facilitate desirable production properties in the  Bay.  Food
web analysis and  bioenergetics modeling can be effective in
this regard. Network analysis (Baird and Ulanowicz  1989)
has provided  a  good  start to define  the  linkages  and
connectedness of key  species  and  their  relationship  to
component subsystems. Pimm et al. (1991)  offer encourage-
ment  in  the use of food web theory to define  "health"  in
systems and changes in status over time.

Bioenergetics  modeling can be particularly effective  in
clarifying how food availability and temperature link forage
species to  predators  in a functional way (Hewett  1989,
Hewett and Johnson 1989). In a simulation mode, bioener-
getics models can be used to predict how changes in habitat
that affect organism distribution (e.g., dissolved oxygen  or
temperature), combined with estimates of organism abun-
dances, will affect productivity of key species. In more com-
plex multispecies bioenergetics models, predator and  prey
dynamics and productivity can be modeled, an effective way
to learn  how  piscivore production depends upon that  of
forage fishes.  A bioenergetics and  food web approach  to
modeling in the Chesapeake Bay will add  an important
"top-down" perspective to the "bottom-up", nutrient-driven
modeling that now predominates.

Some  key  species,  because  of their  dominant status  in
ecosystems or their economic value, require both intensive
monitoring and application of modeling approaches to un-
derstand their dynamics  in Chesapeake  Bay.  Individual-
based  models (IBM),  in contrast to  models that depend
upon estimated  population  parameters, follow the fates  of
individual organisms through  their life. These  models are
becoming  increasingly  popular  among  fish  ecologists
(Huston  et al. 1988)  and are  being  developed for  some
species that are  important  in  Chesapeake  Bay,  e.g., bay
anchovy  (Cowan el al., in prep.) and  striped bass (Cowan
and Rose  1991, Rose and  Cowan,  submitted). In  IBM
models, the dynamics of large populations  are simulated  by
applying  expected  rates  or probabilities  to  individuals
throughout  their lives. Population-level consequences are
sensitive  to changes in habitat quality,  food availability, and
predator-prey  relationships  as they  affect  growth  and
survival of individuals at each life stage. The IBM approach
is attractive  because it allows relatively fast exploration via
simulation of the  consequences of changes in biotic  or
abiotic variables on target species dynamics. If an IBM is to
be applied  effectively, a  considerable base of biological
knowledge, not  only species-specific information but also
life-stage specific material, is required.

                RECOMMENDATIONS

The realities  of budgets and  affordability constrain  all
ecosystem  research. In the  case  of  ecologically valuable
fishes, status  indicators that incorporate  fish community
surveys and habitat evaluation  into various indices, includ-
 52

-------
in
 ing the  Index of  Biotic  Integrity  0ordan  et  al.  1991),
 potentially can show temporal and spatial trends (Vaas and
 Jordan 1991).  Survey collections from which such indices
 can be developed are carried out routinely in Bay tributaries
 and can be applied effectively for tributary habitats. Equiva-
. lent surveys in the Bay proper that might index forage fish
 abundance would require greater and more costly efforts.

 Affordable  research  and  modeling that  focus on  the
 functional aspects of forage  fish  biology can provide  the
 knowledge required  to determine what,  if  any,  additional
 monitoring efforts are needed. Some modeling approaches,
 for example,  bioenergetics modeling,  are  developed well
 enough for fishes so that modest research efforts on Bay
 species may be rewarding. For some presumed key species,
 such as bay anchovy and menhaden, there  already may be
 enough  data  on  fish  abundance,  prey abundance and
 consumption rates,  as well  as temperature data, -to develop
 bioenergetics models and apply them  to Chesapeake Bay.
 The same may be said for individual-based modeling on bay
 anchovy and menhaden.

 The coastwide  fish production analysis by Peters and Schaaf
 (1991), which  concluded that the dearth of understanding
 of forage fish  production was a major gap in  knowledge,
 holds true for Chesapeake  Bay. A research effort to  deter-
 mine  the nature and cost of forage fish production is
 appropriate. Modeling  efforts (food webs,  bioenergetics,
 IBM,  ecosystem)  are perhaps  the only way to  define and
 quantify the probable importance of forage  fishes  in  the
 Bay ecosystem. Some routine, and probably not very costly,
 additional monitoring of forage fishes may be desirable but
 adoption of new programs seems unwarranted until research
 and modeling results convince us of the  need.

                     REFERENCES

 Baird, D. and R.E. Ulanowicz. 1989. The seasonal dynamics
 of the  Chesapeake Bay ecosystem.  Ecological Monographs
 59: 329-364.

 Cowan, J.H., Jr.  and K.A. Rose. 1991. Potential effects  of
 maternal  contribution  on  egg  and   larvae  population
 dynamics of striped bass: Integrated individual-based model
 and directed field sampling. International Council Explor.
 Sea. CM. 1991/Mini:6. 15 pp.

 Hewett, S.W. 1989. Ecological applications of bioenergetics
 models. American Fisheries Society Symposium 6: 113-120.
 Hewett, S.W. and B.J.Johnson. 1989. A general bioenergetics
model for fishes. American Fisheries Society Symposium 6:
206-208.

Houde, E.D.  (ed.)  1987. Long-range research  needs for
Chesapeake Bay living resources. Center for Environmental
and Estuarine Studies, UMCEES Technical Series No. TS61-
87.

Huston, M., D. DeAngelis and W. Post. 1988. New comput-
er models unify ecological theory.  Bioscience 38:  682-691.

Jordan, S.J.,  P.  Vaas and J.  Uphoff. Fish assemblages  as
indicators of environmental quality in northern Chesapeake
Bay. In: Biological Criteria: Research and Regulatin  1990.
Proceedings of a symposium, Crystal City, Virginia, Decem-
ber 1990. USEPA Office of Water. Washington, D.C.

.Klebasko, M.J. 1991. Feeding ecology and daily  ration of
bay anchovy (Ancboa mitcbilli) in the mid-Chesapeake Bay.
Master's Thesis, University of Maryland, College  Park. 115
pp.

Peters, D.S. and W.E. Schaaf. 1991. Empirical model of the
trophic basis  for fishery yield in  coastal  waters of the
eastern USA. Transactions of the American Fisheries Society
120: 459-473.

Pimm, S.L, J.H.  Lawton and J.E. Cohen. 1991. Food web
patterns and their consequences. Nature 350: 669-674.

Purcell, J.E.  and D.A.  Nemazie. In press.  Quantitative
feeding ecology of  the hydromedusan Nemopsis bachei in
Chesapeake Bay.  Marine Biology.

Rose, K.A.  and J.H. Cowan, Jr. Submitted. Individual-based
model of young-of-the-year striped bass. I. Model descrip-
tion and baseline simulations. Transactions of the American
Fisheries Society.

Vaas,  P.A.  and  S.J.  Jordan.  1991.  Long-term  trends in
abundance indices for 19 species of Chesapeake Bay fishes:
reflections of trends  in the Bay ecosystem. In: J.A. Mihursky
and A. Chaney (eds.), New perspectives in  the Chesapeake
System: a research and management  partnership.  Proceed-
ings of a Conference, 4-6 December  1990, Baltimore, MD.
Chesapeake Research Consortium Publ. No. 137.

Vazquez, A.V. 1989. Energetics, trophic relationships and
chemical composition of bay anchovy, Anchoa. mitchilli, in
the Chesapeake Bay. Master's Thesis, University  of Mary-
land,  College Park. 166 pp.
                                                                                                                            53

-------
1
"A

-------

Daniel M. Dauer
Dept  of Biological
Sciences
Old Dominion  University
Norfolk, Virginia

                  INTRODUCTION
     J. Gerritsen
     Versar,  Inc.
  ESM Operations
  9200 Rumsey Rd.
Columbia, Maryland
    J. A.  Ranasinghe
           Versar, Inc.
     ESM Operations
    9200 Rumsey Rd,
Columbia, Maryland
The benthos consists of organisms that dwell on the bottom
of  marine,  estuarine  and  freshwater  ecosystems.  This
synopsis  is  restricted  to the macrobenthic  infauna of
sedimentary habitats because this group of the benthos is
emphasized  by the Chesapeake Bay biological monitoring
programs in both Virginia and Maryland. These are animal
species retained on  a 0.5 mm screen when processing
sediment samples. Estimates of the macrobenthic infaunal
community  are used to indicate  environmental health be-
cause benthic  animals (1) are relatively  sedentary  (cannot
avoid water  quality  problems), (2) have relatively long  life
spans (indicate and integrate  water quality problems over
time),  and  (3) consist  of species that exhibit different
tolerances to stress (benthos can be classified into functional
groups based on tolerances to water quality stresses). Species
of benthos  that are  commercially  important and  are
generally epifaunal  (dwell  at or on the  sediment-water
interface) are not covered in this  synopsis.

         BENTHIC SPECIES

The macrobenthic infauna of the Chesapeake Bay  consists
of more than  300 species belonging to many  invertebrate
groups. Representative species  are best characterized by  the
biomass dominants of the major salinity  regions of  the
Chesapeake Bay, as presented  in  Table 1. The  distribution
and abundance of benthic species is  controlled by several
environmental factors,  with salinity the primary determi-
nant. Sediment type and dissolved oxygen concentration are
important secondary factors influencing benthic community
composition in Chesapeake Bay (Holland et al. 1988,  1989;
Dauer el al. 1989; Shaughnessy et al. 1990; Scott et al. 1991).

In the polyhaline lower Bay, the dominant functional group
consists of subsurface deposit  feeders, and suspension feed-
ers are of secondary importance (Holland a al. 1988,  1989;
Dauer  et  al.  1989). In  other areas  benthic  biomass is
dominated by  obligate and facultative suspension feeders.

       BENTHOS IN THE BAY ECOSYSTEM

The benthos have important ecological roles in (1)  control-
ling water quality by removing phytoplankton (Table 2) and
                other  suspended particles; (2) nutrient recycling through
                feeding, ventilation and sedimerit alteration  activities; (3)
                trophic dynamics and energetics  as important food sources
                for higher trophic levels including fish and blue crabs; and
                (4) affecting the flux of sediment contaminants through bio-
                turbation and  transfer of contaminants to higher trophic
                levels through uptake (Berner 1976; Aller 1978, 1982; Virn-
                stein 1979; Holland et al. 1980; Swartz and Lee 1980; Boesch
                and Rosenberg 1981; Cloern 1982; Dauer et al.  1982a, b;
                Hartley 1982; Hargrave  and Theil 1983; Officer et al. 1982;
                Phillips and Segar 1986; Bilyard 1987;  Gerritsen 1988; Gray
                et al. 1988; Warwick et al. 1990; Western 1990).

                Macrobenthic production in Chesapeake Bay is moderate to
                high, but varies markedly among regions and habitats. Tidal
                fresh and transitional  habitats  are the most productive,
                where annual production of the suspension feeding bivalves
                Rangia and Corbiada can reach  several hundred  g  m~2  y'
                (Holland et al.  1989). The deep,  high  mesohaline portions
                of the mainstem and Potomac River are the least productive
                habitats, because they are subject to annual hypoxia in the
                summer months. Total annual production in  these habitats
                is less than 1 g  m"2 y"1. Hypoxic conditions  also occur in the
                deeper portions of the mouths of several  tributaries  along
                the  central mainstem (e.g. Patuxent  and Patapsco  rivers;
                occasionally Choptank, Chester, and Rappahannock rivers),
                and as a result  macrobenthic productivity in these habitats
                is also relatively low (Holland et al. 1989; Shaughnessy et al.
                1990).

                        BENTHIC INDICATORS OF STRESS

                Currently there  is  no  consensus  on the  best benthic
                indicators   of  stress;   however,   unstressed   benthic
                communities can be characterized by (1) high biomass, (2)
                high species diversity  and (3)  community  composition
                dominated in  biomass  by long-lived,  often deep-dwelling
                equilibrium  species.  Figure  1  represents  an analysis  of
                environmental  stress  using graphical  models of expected
                community parameters  based upon macrobenthic infaunal
                data from the  Virginia  benthic biological monitoring pro-
                gram  (see Dauer el  al. 1989  for  further details of the
                sampling program). This is one approach to quantifying
                expected benthic community parameters.
                                                                                                                55

-------
Table 1. Representative benthic taxa for the major salinity regions of the Chesapeake Bay.
    Tidal Fresh
    Transitional
    Mesohaline
    Polyhaline
midge larvae
oligochaetes
clam

polychaete
clam
crustacean

polychaetes
                                    clams
                                    crustaceans
                                    nemertean worm
polychaetes
                                    clams
                                    mud shrimp
                                    anemone
Chironimids, Chaoborids
Limnodrilus
Corbicula

Marenzelleria
Rangia
Leptocheirus, Cyathura, Gammarus

Marenzelleria,  Heteromastus,   Nereis,  Streblospio,  Eteone,
Paraprionospio, G/ycinde

Macoma, Rangia, Mya, Mulinia, Gemma
Leptocheirus, Cyathura, Monoculodes
Carinoma
Asychis,  Chaetopterus,   Clymenella,   Diopatra,   Loimia,
Macroclymene,   Nephtys,  Notomastus,  Pseudeurythoe,
Spiochaetopterus
Ensis, Mercenaria, Te/lina
Upogebia
Cerianthus
Table 2. Removal of phytoplankton by suspension feeders was estimated from benthic and plankton production estimates, and from a model
of suspension feeding (Gerritsen 1988, Holland ef at. 1989). These findings suggest that macrobenthos are at least equivalent to zooplankton
in overall importance as consumers of  phytoplankton,  and that benthos are the most important consumers  in shallow  reaches. Uneaten
phytoplankton cells are available to bacteria and planktonic protozoa, and can contribute to the development of hypoxic conditions in the central
mainstem of the Bay. Malone et al. (1986) estimated that approximately 60% of primary production was consumed by bacteria in the central
rnainstem.
                     Habitat Type

                     Tidal Fresh, shallow

                     Low Mesohaline

                     High Mesohaline, deep
                             Primary Production Consumed

                             50-80%

                             30-50% (zooplankton crop same amount)

                             10-15% (zooplankton crop 20-30%)
Models of expected values of macrobenthic  community
structure  are  presented  for  six  measurable  attributes.
Foremost among these is species richness, or the number of
species encountered, since within a habitat, stable, relatively
unstressed habitats tend  to support more species. Two other
attributes  commonly used  to characterize  macrobenthic
community structure are community biomass and numbers
of  individuals. Three  parameters less often  used,  but
promising for the future are: the presence and contribution
of   deep-dwelling  species,   equilibrium   species,   and
opportunistic species. Models present mean values for each
parameter from 1985 through 1989 with 95°/o  confidence
intervals plotted against salinity. In the absence of reliable
historical data from pristine habitats, stations  considered
minimally impaired were  chosen to  calculate expected
                              values. Values  for two stations  (SBE2  and  SBE5)  from
                              highly contaminated sediments of the Southern Branch of
                              the Elizabeth River consistently deviated from expectation
                              (also shown  in Figure  1). Evaluation of restoration efforts
                              could use such models with the expected values serving as
                              restoration "goals".

                              Based on the indicator of benthic species richness, we can
                              identify  two problem areas and  a suspected  third in  the
                              upper Chesapeake Bay (Scott et al. 1991). First is the central
                              mainstem, which is depauperate and stressed  from annual
                              summer  hypoxia and anoxia. Second, portions of Baltimore
                              harbor are depauperate, most likely due to toxic substances
                              in the sediment. The third habitat of concern is tidal fresh
                              regions,  where some areas had  depauperate  benthos, but
56

-------
 100
                           SBE5 •
                                      SBE2
      BIOMASS (g/m2)

    0      5
                                                        10000
                                                         1000
                 10       15       20
                     SALINITY (ppt)
                                            25     30
                                                        100
                                                                              10      15       20
                                                                                  SALINITY (ppt)
                                                                                                    SBE2
                                                                                                      25
                                 30
                                                                    DEPTH DISTRIBUTION of BIOMASS

                                                                      5
1  SPECIES DIVERSITY (sp/rep)

         5      10       15       20
                   SALINITY (ppt)
  0


100 %
10      15       20
   SALINITY (ppt)
 10%
         EQUILIBRIUM SPECIES BIOMASS
                     10       15      20
                         SALINITY (ppt)
                                                                           10       15      20
                                                                               SALINITY (ppt)
Figure 1. Relationships between community parameters as a function of salinity. Salinity values are five year means (1985-1989) and 95%
confidence intervals (n=60). Line shown is a splined curve to aid visual interpretation. Comparison of expected community parameters with
stations exposed to contaminated sediments of the Southern Branch of the Elizabeth River (SBE2 and SBE5). Values for SBE2 and SBE5 are
mean  values for data from 1989  (n=12). A. Community biomass in g/m2, B. Number of individuals per m2, C. Species diversity in
species/replicate. D. Deep-dwelling biomass as percentage of community biomass below 5 cm. E. Percentage of community biomass composed
of equilibrium species, F. Percentage of community biomass composed of opportunistic species.
                                                                                                               57

-------
 if
.. i
 : i
'Hi
BS
with no known instances of hypoxia or sediment toxicity.
Tidal fresh habitats  are the first to  receive  stormwater
runoff and the pollutants associated with runoff, and some
species may be  sensitive to ephemeral  runoff phenomena
(Hall 1987),  reducing species richness  of tidal  freshwater
habitats.

              BENTHIC RESTORATION

The first  step  for restoring  benthic  community  integrity
throughout the Bay will be to  reduce  the frequency  and
severity of hypoxia so that benthic diversity  is restored in
many  of the  areas  now periodically  impacted  by  low
dissolved oxygen. It must be noted that the deepest portions
may  have  experienced  periodic  hypoxia  even before
European  settlement because of the reduced circulation
during summer stratification, and that  no restoration may
occur in those areas. The second step for benthic restoration
will be to reduce the sediment  toxicity  of  industrialized
embayments, such as Baltimore harbor and  the Elizabeth
River.

Currently,  in the Maryland mainstem Bay, up to 60% of
the total  primary production is not consumed by benthos
or macrozooplankton, and is available  to, and apparently
consumed by, microzooplankton and bacteria  (Malone et al.
1986; Holland etal. 1989). Respiration of microzooplankton
and bacteria below the summer pycnocline is  implicated in
the development of summer hypoxia in  Chesapeake Bay.
The severity of the summer  hypoxic events  could be less-
ened  by  a reduction  of mid-Bay  primary production
brought about by a decrease in the stocks of limiting nutri-
ents, or by increased  cropping of the phytoplankton pro-
duction.

A suspension feeding model has been used to examine the
feasibility of using suspension feeding bivalves to crop and
remove excess primary production from Chesapeake Bay as
a means of improving water quality and reducing summer
oxygen  deficits  (Gerritsen  et  al.  1989).   The  analysis
considered  three  methods  of  biological  water quality
control: (1) bivalve  (oyster)  culture,  (2)  riparian buffers
along streams in the Bay watershed, and (3) use  of SAV to
control nutrients. Raft mariculture  of oysters  may be a
viable means for enhancing water quality and reducing the
frequency and severity of hypoxic events  in the mainstem
Bay and Potomac. It would require the  development of an
extensive oyster mariculture  and support industry. While
there are a host of technical  problems  that  remain to be
solved  to make oyster mariculture feasible, it could  have
major economic benefits for  the Bay region in addition to
contributing to improved water quality.

These pollution control strategies are subject to  limiting
returns on investment as the  reduction goal is approached.
The high oyster production required to remove substantial
phytoplankton production may exceed demand for the
product, requiring subsidies  to  continue the  program.
Similarly, forest or wetland buffers on streambanks may
require as much as 5% of agricultural  and residential land
area for substantial nutrient reduction,  increasing resistance
to such a program and possibly driving land prices higher
as the goal is approached. We therefore  recommend  an
integrated  approach:  tertiary  and advanced treatment to
reduce point source loadings; economically sustainable raft
mariculture of oysters to improve Bay water quality, and
forest and  wetland buffers  along selected streams to reduce
non-point  source nitrogen  loadings.  The  preliminary
conclusions presented here need to be refined, and if they
appear to be valid, a research plan for  testing them should
be developed.

               RECOMMENDATIONS

Monitoring
Benthic monitoring programs emphasizing  macrobenthic
infauna  are  essential   components   of  any  estuarine
monitoring program and should  be recognized  as having
three primary objectives:

(1)  to  characterize the  health of the  Chesapeake  Bay as
indicated by the structure of the benthic communities,

(2) to perform trend  analyses on  long-term data to relate
spatial and temporal trends of the benthic communities to
changes in  water quality  within  the Chesapeake Bay,

(3) to warn of environmental degradation by producing an
historical data base that will allow updated  annual evalu-
ations of biotic impacts due  to changes in water  and/or
sediment quality.

(4) Validation of benthic indicators.

Research
The following four areas  represent research  needs relative to
the benthos:

(1)  Understanding the  functional relationship  between
nutrient reduction strategies, benthic nutrient flux dynamics
and the composition of  benthic communities.

(2)  Understanding the  functional relationship  between
sediment contaminant levels, sediment contaminant flux
and bioturbation activities of the benthos.

(3) Understanding the functional relationship of benthic
secondary  production and dynamics  of higher trophic
levels.
             58

-------
1C
ic
(4) Development of biological criteria for benthos  to serve
as restoration goals for management.

Because of the complexity of the estuarine  system  and the
diversity  of benthic  species  in  the Chesapeake  Bay,  a
functional group approach for each major salinity region is
essential.  Functional  groups can be  defined based on (1)
feeding  characteristics (e.g.  suspension feeding,  surface
deposit feeding, subsurface deposit  feeding), (2) sediment
alteration characteristics (e.g. sediment stabilizers, sediment
destablizers; see Woodin 1983), (3) life history characteristics
(e.g.  equilibrium  species,   opportunistic  species,  stress
tolerant species) or (4) combinations of the above groups.

Modeling
Future water quality modeling efforts  should  include the
benthos  and  emphasize  functional groups  based  upon
results from research recommended above. Relationships
between benthos and  higher trophic levels (including many
species of economic  and  commercial importance) within
years  are well  known; however, predictable relationships
between years are  much less certain (Arntz 1980; Woodin
1983).

Habitat
Various attempts to define  critical life  stages  and  critical
habitats are well intended efforts to direct limited resources.
However, the implication that there are less  critical  or even
non-essential habitats  is contrary to the primary  goal of
restoring a balanced ecosystem. Relative to the benthos, the
primary habitat recommendation would be the promotion
of vegetation  in  (1)  shallow subtidal  habitats  (SAV), (2)
intertidal habitats  (salt marsh  grasses  and (3) bordering
terrestrial habitats (buffer strips). These plant communities
act as filters (removing nutrients and sediments), nurseries
and ecological refuges.

                     REFERENCES

Aller, R.C. 1978. The effects of animal-sediment interactions
on geochemical processes near the sediment-water interface,
In: Estuarine Processes, (M. Wiley, ed.) pp. 157-172,  Aca-
demic Press, New York.

Aller, R.C. 1982. The effects of macrobenthos on chemical
properties of marine  sediments and overlying water. In:
Animalsediment relations (P.L.  McCall  and M.J.S.  Tevesz,
eds.),  pp. 53-102,  Plenum Press, New York.

Arntz, W.E.  1980. Predation  by demersal fish and its impact
on  the dynamics of macrobenthos, In: Marine  benthic
community  dynamics (K.R. Tenore  and B.C.  Coull,  eds.),
pp. 121-149, University of South Carolina Press, Columbia,
South Carolina.
 Berner,  R.  1976. The  benthic boundary  layer from the
 viewpoint of a geochemist. In: The benthic boundary layer,
 0. McCave, ed.) pp. 33-55, Plenum Press, New York.

 Bilyard, G.R.  1987. The value of benthic infauna in marine
 pollution monitoring studies. Marine Pollution Bulletin 18:
 581-585.

 Boesch, D.F. and R. Rosenberg. 1981. Response to stress in
 marine benthic communities. In: Stress effects on natural
 communities (G.W. Barrett and R. Rosenberg, eds.), pp. 179-
 200. John Wiley, London.

 Cloern, J.E. 1982. Does the benthos control phytoplankton
 biomass  in South San  Francisco Bay? Marine  Ecology
 Progress Series 9: 191-202.

 Dauer,  D.M.,  R.M Ewing, G.H. Tourtellotte, W.T. Harlan,
J.T. Sourbeer, and H.R. Barker Jr. 1982a. Predation pressure,
 resource limitation and the structure of benthic infaunal
 communities. Int. Revue  ges. Hydrobiol. 67: 477-489.

Dauer,  D.M.,  G.H. Tourtellotte, and R.M. Ewing. 1982b.
Oyster shells and artificial worm tubes: the role of refuges
in structuring benthic infaunal communities. Int. Revue ges.
Hydrobiol. 67: 661-677.

Dauer, D.M., R.M. Ewing, J.A. Ranasinghe, and A.J. Rodi,
Jr.   1989.   Macrobenthic  communities   of  the lower
Chesapeake Bay. Chesapeake Bay Program. Final Report to
the Virginia Water Control  Board. 296 pp.

Gerritsen, J.  1988.  Biological  control of water  quality in
estuaries:  Removal of paniculate matter  by  suspension
feeders. Proceedings, Oceans 88: 948-956, IEEE.

Gerritsen, J., J.A. Ranasinghe, and  A.F.  Holland.  1989.
Comparison of three strategies to improve water quality in
the Maryland  portion  of Chesapeake Bay. Appendix C in:
Holland et al.  1989 (op. at.).

Gray, J.S., M.  Ascan, M.R. Carr, K.R. Clarke, R.H. Green,
T.H. Pearson, R. Rosenberg and R.M. Warwick. 1988. Anal-
ysis of community attributes of the benthic macrofauna of
Frierfjord/Langesundfjord and in a mesocosm experiment.
Marine Ecology Progress  Series 46: 151-165.

Hall,  L.W., Jr.  1987. Acidification  effects on  larval striped
bass,  Morone  saxatilis, in Chesapeake Bay tributaries: A
review. Water, Air, and Soil Pollution 35: 87-96.

Hargrave, B.T. and H. Theil.  1983. Assessment of pollution-
induced changes  in benthic  community structure. Marine
Pollution Bulletin 14: 41-46.
                                                                                                                             59

-------
-ff
 1
 1
 i
'1
Hartley,  J.P.  1982.  Methods  for  monitoring  offshore
macrobenthos. Marine Pollution Bulletin 13: 150-154.

Holland,  A.F.,   N.K.  Mountford,  M.H.  Hiegel,   K.R.
Kaumeyer and J.A.  Mihursky. 1980. Influence of predation
on infaunal abundance in upper Chesapeake Bay. Marine
Biology 57: 221-235.

Holland, A.F., A.T. Shaughnessey, L.C. Scott, V.A. Dickens,
J.A. Ranasinghe and J.K. Summers. 1988. Long-term benthic
monitoring and assessment program for the Maryland por-
tion of Chesapeake Bay 0uly  1986-June 1987). Maryland
Department of the Environment and Maryland Department
of Natural  Resources,  Power Plant  Research  Program,
Report No.PPRP-LTB/EST-88-1.

Holland, A.F., A.T.  Shaughnessey, LC. Scott, V.A. Dickens,
J.  Gerritsen and J.A. Ranasinghe.  1989. Long-term benthic
monitoring  and  assessment  program  for  the  Maryland
portion of Chesapeake Bay: Interpretive Report. Report to
Maryland Department of Natural Resources, Power  Plant
Research Program, CBRM-LTB/EST-89-2.

Malone,  T.C, W.M. Kemp, H. Ducklow, W.R. Boynton,
J.H. Turtle and  R.B. Jonas.  1986.  Lateral variation in the
production  and  fate  of phytoplankton  in   a  partially
stratified estuary. Marine Ecology Progress Series 32: 149-
160.

Officer, C.B., T.J. Smayda and R. Mann. 1982. Benthic filter
feeding: a natural eutrophication  control.  Marine Ecology
Progress Series 9: 203-210.

Phillips, D.J.H., and D.A. Segar. 1986. Use of bio-indicators
in  monitoring   conservative   contaminants:  programme
design imperatives.  Marine Pollution Bulletin 17: 10-17.

Scott, L.C., J.A. Ranasinghe, A.T. Shaughnessy, J. Gerritsen,
T.A. Tornatore, and R. Newport.  1991. Long-term benthic
monitoring  and  assessment  program  for  the Maryland
portion of Chesapeake Bay: Level I comprehensive  report
(July 1984-April 1991). Prepared for Maryland Department
of the Environment and Maryland Department of Natural
Resources.

Shaughnessy,  A.T.,  LC.   Scott,  J.A.   Ranasinghe, A.F.
Holland, and T.A. Tornatore. 1990.  Long-term benthic
monitoring and assessment program for the Maryland por-
tion of Chesapeake Bay: Data summary and  progress report
0uly 1984-August 1990). Prepared for Maryland Department
of the Environment and Maryland Department of Natural
Resources.

Swartz, R.C. & J. Lee, II. 1980. Biological processes affecting
the distribution of pollutants in marine sediments.  Part I.
Accumulation, trophic transfer, biodegradation  and  migra-
tion, In: Contaminants and sediments, Vol. 2,  Analysis,
chemistry, biology, (R.A. Baker, ed.) pp.  533-554, Ann Arbor
Science, Ann Arbor, Michigan.

Virnstein,  R.W.  1979.  Predation  on   estuarine  infauna:
response patterns of component species. Estuaries 2: 69-86.

Warwick, R.H., H.M. Platt, K.R.  Clarke, J. Agard  and J.
Gobin.  1990. Analysis of macrobenthic and meiobenthic
community structure  in relation  to  pollution and  distur-
bance   in   Hamilton  Harbor,  Bermuda.  Journal  of
Experimental Marine  Biology and Ecology  138: 119-142.

Weston,   D.P.   1990.   Quantitative    examination  of
macrobenthic  community  changes   along  an  organic
enrichment  gradient.  Marine  Ecology Progress Series  61:
233-244.

Woodin, S.A. 1983. Biotic  interactions  in  recent marine
sedimentary environments, In: Biotic interactions  in recent
and  fossil  benthic  communities,  (M.J.S. Tevesz  and P.L.
McCall, eds.), pp. 3-38.
             60

-------
             OYSTEE REEFS
             Roger I.E. Newell
             Horn  Point Environmental Laboratory
             University of Maryland
             Cambridge,  Maryland
                                                                                                Denise Breitburg
                                                                                  Academy of Natural Sciences
                                                                                Estuarine Research Laboratory
                                                                                             Benedict, Maryland
me
ent
'.L
     INTRODUCTION AND REPRESENTATIVE
     SPECIES PRESENT IN CHESAPEAKE BAY

The economic significance of the eastern oyster harvest in
Chesapeake  Bay has long been recognized  (Kennedy and
Breisch 1981) and  the  continuing decline  in harvests is
adversely affecting the economy of many fishing communi-
ties. What is only now becoming widely appreciated is the
importance of the oyster in the natural functioning of the
complex ecosystem  that is Chesapeake Bay.  Historically,
oysters  may  have been  important in  maintaining water
quality by removing algae and silt from suspension. Further-
more, the hard bottom  substrate formed by natural oyster
reefs (=bars  =rocks) is essential to the existence of many
other benthic organisms, and beneficial to many species of
demersal and pelagic finfish.

Although soft mud bottom benthic communities are cur-
rently predominant within the  Bay (Holland et at. 1989),
only 100 years ago, prior to the major oyster  harvests of the
latter part of the 19th Century, oyster reef communities were
extensive (Newell 1989). In an effort to obtain some of the
benefits historically provided by oyster reefs the Chesapeake
Bay program is currently implementing an "artificial aquatic
reef habitat plan that is directed to increase  the amount of
hard bottom substrate available in Chesapeake Bay  (Myatt
and Myatt 1990).

The  sessile  invertebrate assemblage  that grows on and
among  oysters  forms  a temporally and spatially complex
community  that includes many species. Among  the most
abundant sessile and  sedentary  invertebrates are  barnacles
(Balanus improvisus), bent mussels (Brachidontes recurvum),
bryozoans  (Electra  crustulenta  and Membranipora  tenuis),
tunicates (Mogula. manbattensis),  and mud worms (Polydora
ligni) (Dame 1976, 1979).

Oyster reefs also provide habitat and food resources for a
number of mobile species that are ecologically important to
the Chesapeake  Bay  ecosystem.  Both the density and
diversity of some taxa of mobile fauna  are considerably
higher  within oyster reefs than  over adjacent soft bottom
habitat. Common mobile invertebrates include amphipods
(especially Cowphium lacustre), which are important prey of
fishes (Hildebrand and Schrbeder 1927), xanthid mud crabs,
and the blue crab  (Callinectes sapidus). In addition, over a
dozen species of benthic and demersal fishes utilize meso-
haline oyster reefs during summer in Chesapeake Bay. The
abundance of these  benthic  fish in oyster reefs  without
heavy sediment load can be extremely  high; densities of
naked goby (Gobiosoma base) in excess of 30 individuals/m2
have been reported for both Maryland and Virginia oyster
reefs (Nero 1976; Breitburg 1992). Besides reef-dependent
fish, many other benthic and demersal fishes including spot
(Leiostomus xanthurus),  striped bass  (Morone  saxatilis)  and
black  drum (Pogonia cromis) regularly forage on oyster reefs
and remain in close proximity to reefs for extended periods
of time.

Interactions among species  are important factors that lead
to the actual community composition on oyster reefs even
though some of these interactions may limit the abundance
of oysters. For example,  there  are  complex competitive
interactions among various sessile invertebrates (barnacles,
tunicates,  bryozoans, etc.) and oysters for space (Osman et
al. 1989).  Such competition may influence the success of
oyster recruitment  onto  the limited  hard  substrate  in
Chesapeake Bay. In addition, several mobile  invertebrates
commonly found in oyster reefs are important predators of
oyster spat. Among these are the  blue crab  (Callinectes
sapidus), xanthid crabs (including Eurypanopeus depressus and
Panopeus  herbstii),  and the  flatworm  Stylochus  ellipticus
(McDermott 1960; Krantz and Chamberlin 1978; Bisker and
Castagna  1987; Newell et al. 1990; Abbe and Breitburg
1992). Small spat are most susceptible  to these predators,
and predation is likely to be an important factor influenc-
ing the recruitment of spat to existing reefs.

         IMPORTANCE OF THESE SPECIES

It  is  self-evident that  the  oyster is the most  important
organism within the  oyster reef community. This is due to
the importance of oyster  shell in providing  a  settlement
substrate for  sessile  invertebrates and  shelter for mobile
species.  Oysters, and other suspension  feeding organisms
that  form part of the   reef  community (e.g.  mussels,
tunicates, barnacles, etc.), can improve water quality because
their feeding activity significantly reduces suspended particle
                                                                                                                             61

-------
concentrations in  estuarine  waters  (Newell  1988).  The
resulting biodeposits can form  an important food  source
for other  oyster  reef  residents,  thus increasing species
diversity and biomass.  This  enhanced  biodeposition by
oysters serves to sequester nutrients into sediments, reducing
their availability in the  water column.

The sessile species that constitute the reef community are an
important component of the food web in Chesapeake Bay,
providing a  source of food for  many  ecologically and
commercial important  predators, such as  the  blue crab.
Mobile members of the reef community, such as the naked
goby, are also important prey items for a  number of larger
fmfish species (Markle  and Grant 1970,  Nero  1976). The
naked  goby   utilizes oyster  reefs for both shelter  and
reproduction.  Its   larvae   are  major   consumers  of
zooplankton   and  thus   constitute  a mechanism whereby
carbon  is transported from the plankton to the benthos.
Naked goby  larvae are  also an  important food  source for
other species as they are generally the first or second most
abundant  species  in  icthyoplankton samples  collected
during summer  in  the  Chesapeake Bay and its tributaries
(Massman et al. 1963, Shenker et al.  1983).

The oyster toadfish,  which is the largest of the resident
oyster  reef fish,  is unique  among Chesapeake Bay fish in
that larval  and early juvenile  development occur within a
guarded  nest (Gudger   1910).  In  all likelihood,  oyster
toadfish remain  on a single oyster reef, or at least within a
very confined geographic area,  from the  adhesive benthic
egg  stage  at least  until   temperatures  begin  to  drop
substantially in autumn. The oyster toadfish is an important
predator of mobile oyster-reef fauna. This, coupled with its
sedentary nature, may make it a useful vertebrate indicator
of local toxics concentrations due to bioaccumulation of
toxics in the  food  chain.

      INDICATORS OF OYSTER REEF STATUS

Traditional  means  of  assessing oyster populations have
focused oh parameters  important  to  the fishery, especially
annual recruitment and  landings. A review of current oyster
monitoring programs and suggestions for improvements has
recently been performed  by a workgroup (Newell  and
Barber 1990).

As outlined above, the species assemblage that comprises the
oyster reef community is highly diverse, ranging from sessile
invertebrates  to mobile  vertebrates. Such diversity makes it
difficult to devise a single monitoring technique that can be
used to quantitatively sample all  components of  the animal
community, especially the mobile species, at a large number
of locations.  Even  quantifying  sessile species is difficult
because their patchy distribution necessitates  that  large
numbers of samples must be taken. The identification and
enumeration of all species within such samples is very time
consuming. Also, each species in the reef community  re-
quires different combinations of salinity and temperature to
flourish. Therefore, there is not just one oyster reef commu-
nity  present  in  Chesapeake Bay  but a  temporally and
spatially complex mosaic of species. Thus, it is  difficult to
define what is the normal or typical species composition of
the oyster reef community at any one location or  sampling
date.

There is little information  available on how to assess the
suitability  and quantity of oysters reefs  as hard bottom
habitat  for reef dwelling species. We  suggest that what is
important  is  a  combination of abundance of the  living
oyster and cultch material  and the  3-dimensional  aspect of
the  reef (=height of  the   material above the  bottom).
Certainly, prior to the overexploitation of the oyster stocks
in the 1880's,  oyster bars were large structures that extended
high  into the  water column. Such a structure, still  extant in
intertidal  oyster  populations  south  of  the  Carolinas,
provides many crevices and surfaces for other  animals to
utilize,  much in the same  way that coral reefs or wrecks
provide  refuges for fish.

Another problem associated with the reduction in  height of
the oysters reefs is the increased susceptibility of the cultch
to siltation. Oyster  larvae require  a clean, silt-free oyster
shell  on which  to attach when they metamorphose from
free-swimming larvae into juvenile oysters. Excessive removal
of  oysters from  oysters reefs  meant  that the  structure
became eroded and vulnerable to siltation associated with
excessive sediment runoff into the bay. Similarly, for many
other  invertebrates   the  value  of the  oyster  shell  is
diminished when it becomes buried by an overburden of
silt.

   QUANTITATIVE TARGETS FOR OYSTER  REEF
                    ABUNDANCE

An obvious target for  the abundance of oyster reefs would
be to reestablish the populations that existed in  the surveys
by Yates at the turn of last century.  Realistically, such a
scenario would be difficult  to achieve due to the lack  of
cultch material to reestablish oyster bars. Also, the continu-
ing epizootics of MSX and Dermo are likely to prevent the
reestablishment  of large oyster  populations in  the higher
salinity  regions  of Chesapeake Bay. Instead, with suitable
management  of  the  bottom cultch,  many of the  lower
salinity  and relatively  disease free regions of the  bay may
once again support a flourishing oyster population.

The  ongoing  discussions concerning  introduction  of the
Pacific oyster, Crqssostrea gigas, as an aquaculture species to
Chesapeake Bay may have important  implications for the
abundance  of cpyster  reefs. It  is possible  that  if  the
62

-------
  "" i"
"  " -"-' J-"
introduced oyster becomes established as a naturally repro-
ducing species, then an increased abundance of reef habitat
will  naturally develop. At this time, however, the potential
positive and  negative ecological effects of introducing of C.
gigas have not been fully evaluated.

In the absence  of disease tolerant  or resistant  oysters to
propagate and establish new oyster reefs, the amount of
hard reef material can not be increased by any management
activity other than physically putting that material on the
bottom.  Much remains to be  learned concerning how such
material  should be  placed in relation to prevailing water
currents  in order  to  reduce siltation. Ultimately, however,
the amount of material  that can be deployed is limited by
the  money available. Also,  cultch material is  becoming a
scarce   resource,   with  adverse  environmental  effects
associated with dredging it from the bottom. One possibili-
ty for improving the existing  bottom material is some type
of active cultivation  to  remove sediment. Work  by DNR
involving bagless dredging has  met with only limited  suc-
cess. More vigorous mechanical agitation with scrapeboards
has been successful in Canada (C. MacKenzie, NMFS-Sandy
Hook, pers.  comm.). Such activities  should be  tested in
Chesapeake Bay.

      RECOMMENDATIONS FOR RESEARCH

Because  of the  variability in abundance and  habitat  re-
quirements  of species  associated  with  oyster  reefs,  the
primary focus of a realistic monitoring program  should be
on the quantity, depth distribution, structure, and  degree of
siltation  of  living oysters  and shell which are  the  key
elements needed to form an oyster reef community. It is im-
practical to monitor  these characteristics of oyster reefs by
SCUBA due to logistical considerations. However,  it may be
practical to  use  underwater  video  cameras mounted on
Remote Operated  Vehicles (ROV) to rapidly survey many
oyster bars and provide a permanent record. Such a survey
could be performed in the fall  when water clarity is maxi-
mal. By  using these techniques on  natural and artificial
oyster reefs it will be  possible  to follow the development of
the hard  bottom invertebrate communities and assess quali-
tative differences between the  two types of substrates. Such
methods should also be used to evaluate innovative meth-
ods  for removing the overburden of silt from cultch on
moribund oyster bars.

On a subset  of reefs, a more thorough sampling program,
using SCUBA divers, ROV, and remote sampling, should be
conducted during summer when visibility is poor but many
important biological and physical events take place.  On
these reefs,  associated  fauna  and macroalgae  should  be
sampled, identified and enumerated, and summer sediment
accumulation should be monitored. It will also be impor-
tant to monitor dissolved oxygen since episodes of severe
hypoxia that have little effect  on oysters  can cause heavy
mortality of associated  fauna  (Breitburg  1990, 1992).  In
addition, juvenile oysters and settlement substrates could be
deployed at this subset of reefs to provide direct measures
of variation in growth, survival and recruitment of sensitive
life stages  of oysters and other sessile invertebrates. The
proposed monitoring of this  subset of reefs  should help
clarify the relationship  between the physical  structure of
oyster reefs and the  development of a typical oyster reef
community. This should provide information needed to set
goals for reef restoration and preservation.  Based on current
knowledge, it can be assumed that high species richness and
high  abundances of species in all trophic levels should be
characteristic of natural oyster  reef communities. However,
no specific data are currently available to permit the char-
acterization of oyster reefs as healthy or degraded based on
associated fauna.

Many aspects of oyster reef communities are  still  poorly
understood. Fundamentally we need  to know if an artificial
reef composed of  fossil  oyster  shell,  or  some substitute
material such as cement, consolidated fly ash, old tires, etc.,
is capable of sustaining as productive an associated commu-
nity as a natural oyster reef, in which  the  hard substrate is
primarily provided by living oysters.  The primary difference
is that  living oysters provide  a large  amount of organic
material from  their  biodeposits as a source  of food  to
associated organisms. In hard-bottom  reefs without  oysters
this supplemental food source is absent.  Thus, we  might
expect that meiofauna  and detrivores,  such as  worms and
crabs, to be less abundant in the artificial reefs. In addition,
some artificial reef structures  may leach toxic compounds
that can be taken up by organisms in the fouling commu-
nity. We suggest that comparative studies  of natural oyster
reefs and artificial reefs  be conducted to elucidate differenc-
es in  invertebrate community composition.

An associated problem is the  lack of information  on the
importance of oyster reefs to  fish populations  in the Bay.
Except  for  species  that require hard substrate for  egg
deposition, we do not have the basic information required
to  assess  how  changes  in  the areal  extent or biological
characteristics of oyster reefs affect population dynamics or
growth rates of fish species that also utilize other habitats.
Such  information is needed for the  establishment of goals
and methods  for oyster  reef restoration, and  for  the  as-
sessment of the success of such programs.


                     REFERENCES

Abbe, G.R. and  D.L  Breitburg. The  influence of oyster
toadfish (Opsanus tau}  and crab  (Callimctes sapidus and
Xantbidae) on survival of oyster (Crassostrea virginica) spat in
                                                                                                                             63

-------
Chesapeake   Bay:  Does  spat  protection  always  work?
Aquaculture 107: 21-31.

Bisker, R. and Castagna, M. 1987. Predation on single spat
oysters Crassostrea virginica (Gmelin) by blue crabs Callinectes
sapidus Rathbun  and  mud crabs Panopeus  herbstii Milne-
Edwards. Journal of Shellfish  Research 6:37-40.

Breitburg, D.L. 1990. Nearshore hypoxia in the Chesapeake
Bay: patterns and  relationships among  physical factors.
Estuarine Coastal and  Shelf Science 30: 593-610.

Breitburg, D.L. 1992. Episodic hypoxia in the Chesapeake
Bay: interacting  effects of recruitment,  behavior and a
physical disturbance. Ecological Monographs 62: 525-546.

Dame, R.F.  1976. Energy flow in an intertidal oyster popu-
lation. Estuarine Coastal Marine Science 4: 243-253.

Dame, R.F.  1979. The  abundance, diversity and bio mass of
macrobenthos on North Inlet, South Carolina, intertidal
oyster reefs. Proceedings National Shellfish Association  69:
6-10.

Gudger, E.W. 1910.  Habits and life history of the  toadfish
(Opsanus tau). Bulletin, U.S. Bureau of Fisheries 28: 1073-
1109.

Hildebrand, S.F. and W.C. Schroeder.  1927. Fishes  of  the
Chesapeake  Bay. Bulletin, U.S. Bureau of Fisheries, Vol.  53,
Pt.  1, 388 pp.

Holland,  A.F., AT.  Shaughnessy, and M.H. Hiegel. 1987.
Long-term variation in mesohaline Chesapeake Bay macro-
benthos: Spatial and temporal patterns. Estuaries  10: 227-
245.

Kennedy, V.S. and LL.  Breisch. 1981. Maryland's oysters:
Research and Management. Maryland  Sea Grant Publication
UM-SG-TS-81-04, 286 pp.

Krantz, G.E. and J.W. Chamberlin,  1978.  Blue crab  pre-
dation on cultchless  oyster spat. Proceedings of the National
Shellfisheries Association 68: 38-41.

Markle,  D.F.  and  G.C. Grant.  1970.  The summer food
habits of young-of-year striped bass in three Virginia Rivers.
Chesapeake  Science  11: 50-54.
Massman, W.H., JJ. Norcross and E.B. Joseph. 1963. Dis-
tribution of larvae of the naked goby, Gobiosoma bosci, in the
York River.  Chesapeake Science 4: 120-125.

McDermott, J.J. 1960.  The  predation  of  oysters  and
barnacles by crabs  of the  family  Xanthidae. Pennsylvania
Academy of Science 34: 199-211.

Myatt, E.N., and D.O. Myatt. 1990. A study to determine
the feasibility  of  building artificial reefs  in  Maryland's
Chesapeake   Bay.  Report  to Maryland  Department of
Natural Resources by International Weighmaster, Inc. 95pp.

Nero,  L.L   1976. The natural history of the naked  goby
Gobiosoma bosci (Perciformes Gobiidae).  M.S. Thesis.  Old
Dominion  University, Virginia, U.S.A.

Newell, R.I.E. 1988. Ecological Changes in Chesapeake Bay:
Are they the result of overharvesting the American oyster
(Crassostrea  virginica)^  Pages  536-546 In:  M.  Lynch,  (ed.)
Understanding the Estuary: Advances in Chesapeake Bay
Research. Chesapeake Research Consortium Publication 129,
Gloucester Point, VA.

Newell, R.I.E., and B.J.  Barber.  1990.  Summary  and
recommendations of the oyster recruitment and  standing
stock monitoring workshop. Maryland Department of Natu-
ral Resources, Annapolis, MD. 32 pp.

Newell, R.I.E., and V.S. Kennedy. 1991. Spatfall monitoring
and partitioning the sources of oyster spat mortality. Final
report to Maryland Department of Natural  Resources. 37
pp.

Osman, R.W., R.B. Whitlatch, and R.N. Zajac. 1989. Effects
of resident species on recruitment into a community: larval
settlement  versus post-settlement  mortality  in  the oyster
Crassostrea virginica. Marine Ecology Progress Series 54: 61-
73.

Shenker, J.M.,  D.J.  Hepner, P.E.  Frere, L.E. Currence, and
W.W. Wakefield. 1983. Upriver migration and abundance of
naked  goby (Gobiosoma bosci)  larvae in the Patuxent  River
Estuary, Maryland.  Estuaries 6: 36-42.

Wolman Committee.   1990.  The role  of  the   State of
Maryland in  oyster fisheries  management. Recommenda-
tions of the Governor's Committee to Review State Policy
for funding Maryland's Chesapeake  Fisheries. Maryland
Department of Natural Resources 90 pp.
 64

-------

     John R. McConaugha
     Old Dominion University
     Department of Oceanography
     Norfolk, Virginia
                                                                                                    Steve Rebacfa
                                                                                        University of Maryland
                                                                                         Eastern Shore Campus
                                                                                      Princess Anne, Maryland
fe-
lt.
                  INTRODUCTION

Crustaceans  are a diverse  group  of animals that  often
occupy key ecological positions in the benthos,  plankton
and microbial communities. Copepods are the dominant
planktonic herbivores in the Chesapeake Bay. Harpacticoid
copepods  are similar to planktonic forms, but are usually
associated with  benthic  communities. Brachyurans, true
crabs, are also important predators in benthic habitats such
as oyster  reefs  and  clam beds. These decapods are also
important prey items for higher trophic  levels within the
bay (striped  bass, American eels, bluefish, etc.) (Manooch
1973;  Wenner  and  Musick  1975;  Wilson et al  1987;
1990a;b).

          NON-DECAPOD CRUSTACEANS

Zooplankton grazing can be a key factor in utilization of
primary production and passage up the food web to higher
trophic levels. Species composition of spring phytoplankton
blooms in stressed marine systems can be altered, often re-
sulting in the  dominance of smaller flagellated species
instead of diatoms. The loss of the normal diatom species
can directly effect feeding efficiencies, growth and survival
of herbivorous  copepod  species. This often results  in in-
creased production of smaller  zooplankton species which
support ctenophores and medusae over  fish  production
(Greve and Parsons 1977). Theories of topdown control in
Chesapeake Bay suggest that jellyfish and  ctenophores may
have  a  significant effect  on  zooplankton  populations,
including copepods and planktonic larval stages of benthic
crustaceans (Feigenbaum and Kelly 1984; Kramer 1979). The
apparent lack of a spring  bloom  in the Elizabeth  River
(Alden et al.  1991) would suggest a major shift in usage of
primary production  away from zooplankton grazers and
towards  the microbial  loop  in the  most industrialized
sections of the bay. Because  of the apparent transfer of large
amounts  of Chesapeake Bay primary productivity into the
microbial  loop further assessment of the fate of this carbon
is required. Transfer of microbial biomass/carbon to higher
trophic levels including planktonic crustaceans remains in
debate. The  general  consensus  is  that crustacean macro-
zooplankton,  while  possessing  the  ability  to   ingest
nanoplankton, do so at very low efficiencies (Ducklow et al.
1986;  Turner et al. 1988). The most common hypothesis for
transfer of microbial carbon is  via  intermediate trophic
levels (Sherr et al. 1986; Stoeckef and Cappuzo 1990; Verity
1991).  A more  direct link between benthic bacterial pro-
duction and higher trophic levels via harpacticoid copepods
has been suggested. Harpacticoid copepods have been shown
to consume  significant  levels  of  bacterial  production.
Harpacticoid  copepod production  can  subsequently  be
passed  up the food web via benthic  invertebrates and de-
mersal   fish.  Alternatively,  there  is  evidence  from
oligotrophic fresh water systems that smaller holoplanktonic
cladocerans can, under the  appropriate conditions, clear
significant levels of nanoplankton biomass from the water
column (Wyle and  Currie 1991). The role of  small crusta-
ceans both in the water column and in the benthos should
not be  immediately dismissed.

             DECAPOD CRUSTACEANS

Given  their dominant  position  in the benthic ecology of
the Chesapeake Bay, large scale changes in decapod crus-
tacean  population size may have long-term implications for
the Bay's ecology.  While it is  not  the only ecologically
important brachyuran in Chesapeake Bay, the blue crab has
received extensive study.

Best known for its economic importance,  the  blue crab
(Callinectes sapidus) is also ecologically important to the Bay.
The blue crab at varying  stages in its life history occupies
several  different trophic levels: herbivore, detritivore, and
carnivore. Prey preference varies with crab size, habitat, and
seasonal availability of prey (Tagatz 1968; Alexander 1986;
Laughlin 1982; Van  Heukelem  1991). Smaller blue crabs
(<60 mm) consume greater quantities of detritus and plant
materials than larger crabs. There is an increased reliance on
predation  with increasing  size.  Adults  are  a  dominant
epibenthic carnivore and scavenger in Chesapeake  Bay and
are important in the predatory control of coastal communi-
ties of the western  Atlantic and Gulf of Mexico  (Hines et
aL, 1990). Blue crab predation on benthic communities can
be significant with bivalves composing  34 to 42% of the
diet. On soft bottoms, they  consume the ecologically and
economically important soft-shelled clam, Mya arenaria and
the Baltic  clam, Macoma baltbica,  which  are  dominant
infaunal components  (Hines and Comtois, 1985). Several
studies have suggested  that  the blue crab may control the
                                                                                                                      65

-------
il
;i
1
size of bivalve and associated fauna populations (Virnstein
1977, 1979, Van Heukelem  1991). The decline  in bivalve
populations  in  the Bay  could result  in  major shifts  in
foraging behavior in the blue crab population.

A major concern of fisheries management is the potential
for  population  over-fishing,  especially in  the face  of
declining catches of other commercially important species
in the bay.

The  chief measure of population abundance for the blue
crab is the commercial landings reported by Maryland and
Virginia. While  there are  problems with catch statistics for
this  species they offer a long-term data record that can  be
used  for  comparative purposes.  Based  on  catch data, the
annual  population level of blue crabs in the bay fluctuates
around a mean level. These annual fluctuations can be wide
but  the  current data suggests that the  blue crab is  main-
taining its population levels despite increasing fishing effort.

A major  contributor to annual  fluctuations is  post-larval
recruitment  from the continental shelf. This recruitment
appears to be dominated by meteorological and physical
processes (McConaugha 1988; Epifanio a al.  1989). Post-
settlement mortality  also  may be  a  major contributor  to
inter-annual  differences  in  population  densities.  Early
juvenile stages ( <25 mm) of the blue crab appear to prefer
grass-bed  habitats to either marsh or sandy bottom habitats
(Orth and van  Montfrons  1987,  1990). The recovery  of
submerged aquatic vegetation (SAV) in the  lower Bay has
increased the availability of this  refuge habitat.  Larger
juveniles (>25 mm) appear to move out of the  grass  beds
and  to prefer sandy bottom areas. For larger crabs, because
of their ability to burrow  rapidly into  the substrate, sandy
bottom  habitats provide  a  better refuge  (Wilson  el  al.
1990a).  Brachyuran  crabs  like  the blue crab  are  most
vulnerable prior to, during, and just after ecdysis of the old
cuticle  (molting). Males  of the  species appear to  utilize
shallow water tidal creeks as a  refuge against  predation
during  the  molt  (Hines  et  al. 1987).  This  suggests that
availability and  quality of shallow tidal creek habitats may
have  a significant impact  on population dynamics  of the
blue crab. Blue crabs inhabit shallow estuarine areas and are
exposed  to  run-off that carries herbicides,  pesticides and
other forms of pollution.  Larval stages are the most suscep-
tible  to poor environmental quality. Habitat requirements
and toxicity data for this species have recently been reviewed
(Van  Heukelem  1991) and will not be dealt with here.

                  RESEARCH NEEDS

The  actual  spawning  stock  size  of the blue crab in  the
Chesapeake Bay appears to vary from year to year 0ones et
al.  1990).  Fecundity per  female also  varies within and
between  years (Prager et  al.  1990). These  reported  inter-
annual differences in reproductive stock size and fecundity
within and  Between years need to be  re-examined to de-
termine their effect on  population dynamics.  Additional
work is required to understand the recruitment dynamics of
this  species.  For example, does post-larval  recruitment or
post-settlement mortality control year class strength?

Recent studies  have suggested a stock-recruitment relation-
ship for C.  sapidm (Tang  1985;  Lipcius  and  Van  Engel
1990).  Data  on the variations  in  reproductive  biology of
this species is needed to fully understand the impact of this
hypothesis on  the long-term" population levels of the blue
crab. If there is a  stock-recruitment relationship which is
somehow coupled  with  the  meteorologically  dominated
larval transport process, the potential for recruit over-fishing
and  a sudden collapse of the fishery is high.  The ecological
as well as the commercial importance of this species dictates
the need for further studies of this species.

               MONITORING ACTIVITY

A long term monitoring  program is needed. Newly hatched
crabs are the principal source  of  crabs hatched two years
hence. There are few reliable measures of blue  crab  abun-
dance at any life history stage. More information is needed
about the life stages in order to understand  natural varia-
tion in crab abundance.  Are fluctuations in abundance of
any life stage related to environmental  variables?

Continued  monitoring  efforts for  this  species  can  be
incorporated into  the annual  catch  statistics and fishery
independent surveys currently in place. Documentation of
reproductive patterns  and  catch  per  unit effort  data in
fishery independent surveys would  provide a more detailed
understanding  of changes in population dynamics. Catch
per unit effort  statistics have been  proposed but implemen-
tation is critical. It would be helpful to obtain better  and
more consistent data on  recreational catch.

It is  important to monitor those areas  of the Bay used for
spawning and nursery areas. We must take greater steps to
prevent deterioration of water quality.  This may require
stronger controls on industry, agriculture and the public to
reduce nutrient loading  and toxic  discharges into the  Bay
and  its tributaries.  Associated research on other indicators
of the "health of the Bay" in general, is vital.

                      MODELING

While  numerous studies  have  documented  the ecological
importance of the brachyuran crabs including the blue crab,
models  addressing  the ecological  effects on the  benthos
following large scale changes in abundance of crabs  (in-
crease  and  decrease) are not available. Because they are
omnivorous, detritivorous, cannibalistic and scavengers, it
            66

-------
is difficult  to  place them at one  trophic level. Because
changes in diet coincide with growth, models should treat
the food web as  dynamic and  flexible in time and space
(Laughlin 1982).  Models  that  incorporate predation  on
bivalve  populations,  especially  spat  and juveniles, may
provide insights  on the  potential  for  reestablishing the
oyster and clam populations in Chesapeake Bay.

The  presence of anoxic conditions  in the Bay during the
summer may also be responsible for crab mortality. Nutri-
ent loading from  agricultural run-off, sewage and  industrial
sources has  caused an increase in oxygen depletion in the
Bay and in its tributaries. Recently this has started earlier in
the summer, affected larger volumes of water  and been
more severe  (Cronin, 1987). More study is needed on causes
and methods of decreasing anoxia.

                   MANAGEMENT

Submerged aquatic vegetation (SAV) beds are an important
habitat for blue crabs, especially during molting. Restora-
tion programs for SAV and remediation of factors involved
in the decline should be continued. The condition of other
habitats such as marshes and oyster beds (which often have
greater densities of crabs than other bottom areas (Cronin,
1987)), and the availability of prey species (which may affect
distribution and  local  abundance of crabs)  must  also be
considered.

Overfishing of any  life stage, molt stage or sex affects the
future of the entire stock.  Knowledge of the life  cycle  and
associated movements  is important  in  making  informed
management decisions.  It  is also necessary  for effective
coordination in management, legislation  and  enforcement
between Maryland  and Virginia. However,  if goals  and
objectives  could be agreed  upon, the regulations would not
have to be uniform.

           GENERAL RESEARCH NEEDS

An area that requires further investigation not only in the
crustaceans  but for all benthic  animals is  the role of
meroplanktonic larvae in water column - benthos ecology.
There are  several  papers that suggest that meroplanktonic
larvae of  benthic invertebrates may remove  considerable
carbon from  the water column during settlement  and
metamorphosis (Bhaud 1979; McConaugha 1992). Transfer
of carbon from the benthos to the water column may  also
occur. Oysters may release up to 50°/o of their biomass as
gametes (Newell, pers. comm.). Larvae of demersal fish may
also  have  an important ecological impact on the  flux of
carbon between the water column and the benthos. Because
larvae tend to feed on  smaller particles they may have a
seasonal effect on carbon flux in the Bay.
                    REFERENCES

Alexander, S.  K. 1986. Diet of the blue crab, Callinectes
sapidus  Rathbun, from nearshore  habitats  of Gaiveston
Island, Texas. Texas Journal of Science  38: 85-89.

Alden, R. W. Ill, R. S. Birdsong, D. M. Dauer, R. M. Erving
and H. G. Marshall. 1991. Lower Chesapeake Bay monitor-
ing program synthesis report: 1985 through 1989. Vol. 3.
AMRL Technical Report 767 p.

Bhaud, M. 1979. Estimation du transfer energetique entre
domaine pelagigue et domaine benthique par  1'intermediaire
du meroplancton lavaire. C. R. Acad. Sci. Paris 288: 1619-
1621.

Cronin, L.E, (ed.). 1987. Report of the Chesapeake Bay Blue
Crab Management Workshop. Parts I & II. 68 pp.

Ducklow, H. W., D. A. Purdie, P. J. LeB. Williams and J. M.
Davies. 1986.  Bacterioplankton: A sink for carbon in  a
coastal marine plankton community. Science 232: 865-867.

Epifanio, C. E., A. K. Masse and R. W. Garvine. 1989.
Transport  of blue  crab  larvae by surface currents  off
Delaware Bay, USA. Marine Ecology Progress Series 54: 35-
41.

Feigenbaum, D.  and M. Kelly. 1984. Changes in the lower
Chesapeake  Bay food  chain in presence of the sea nettle
Chrysaora quinquedrrlia (Scyphomedusa). Marine Ecology
Progress Series 19: 39-47.

Greve, W. and T. H. Parsons.  1977. Photosynthesis and fish
production: Hypothetical effects of climatic  change  and
pollution. Helgo. wiss. Meers. 30: 666-672.

Hines, A. and K. Comtois. 1985.  Vertical distribution of
estuarine infauna in sediments of central Chesapeake Bay.
Estuaries. 8:251-261.

Hines, A., A. Haddon  and L. Wiechert. 1990. Guild struc-
ture and foraging impact of blue crabs  and epibenthic fish
in a subestuary of Chesapeake Bay. Marine Ecology Progress
Series 67:105-126.

Hines, A. H., R.  N.  Lipcus and  A.  M. Haddon. 1987.
Population dynamics and habitat partitioning by size,  sex
and molt stage  of  blue crabs, Callinectes setpidus in a sub-
estuary of central Chesapeake Bay. Marine Ecology Progress
Series 36: 55-64.

Jones, C. M., J. R. McConaugha, P. Gier and M. H.  Prager.
1989. The Chesapeake  Bay blue crab spawning stock 1986
and 1987. Bulletin of Marine Science 46: 159-169.
                                                                                                                 67

-------
Kramer, P. 1979. Predation by the ctenophore, Mnemiopsis
kidyi, in Narragansett Bay, R.I. Estuaries 2: 97-105.

Laughlin,  R. A.  1982.  Feeding habits of the blue crab,
Callinectes  sapidus  Rathbun,  in  the Apalachicola Estuary,
Florida. Bulletin of Marine Science 32: 807-822.

Lipcius, R.  M.  and W.  A. Van  Engel.  1990.  Blue crab
population dynamics in Chesapeake Bay: variation in abun-
dance (York River, 1972-1989) and stock-recruit functions.
Bulletin of Marine Science 46: 180-194.

Manoock, C. S. III. 1973.  Food habits of yearling and adult
striped bass, Morone saxatilis (Walbaum), from Albemarle
Sound, North Carolina. Chesapeake Science  14: 73-86.

McConaugha, J. R. 1988. Export and reinvasion of larvae as
regulators  of estuarine   decapod   populations.  American
Fisheries Society Symposium 3: 90-103.

McConaugha,  J.  R.  1992.  Decapod Larvae:   Dispersal,
Mortality and  Ecology.  A  working hypothesis.  American
Zoology. In press.

Orth, R. J.  and J. van Montfrans.  1987. Utilization of a
seagrass meadow  and tidal marsh creek by blue crabs,
Callinectes sapidus. I. Seasonal and annual variations in abun-
dance with  emphasis on  post-settlement juveniles. Marine
Ecology Progress Series 41: 283-294.

Orth, R. J. and J.  van  Montfrans.  1990.  Utilization  of
Marsh and  seagrass habitats  by early stages of Callinectes
sapidus: A latitudinal perspective. Bulletin of Marine Science
46: 126-144.

Prager, M. P., J. R. McConaugha, C. M. Jones and P. Geer.
1990. Fecundity of  blue  crab, Callinectes sapidus  in  Chesa-
peake Bay: Biological, statistical and  management consid-
erations. Bulletin of Marine Science 46: 170-179.

Sherr,  E.  B.,  B.  F.  Sherr and  G. A.  Paffenhoffer. 1986.
Phagotrophic protozoa as food for metazoans: A "missing"
trophic link in marine pelagic food webs. Marine Microbial
Food Webs  1: 61-80.

Stoecker, D. K. and J. M. Capuzzo.   1990.  Predation on
protozoa: Its importance  to zooplankton. Journal of Plank-
ton Research 12: 891-908.

Tagatz,  M.  E.  1968. Biology of the  blue crab,  Callinectes
sapidus Rathbun, in the  St. Johns River, Florida. Fisheries
Bulletin 67: 17-33.
Tang, Q, 1985. Modification of the Picker stock recruitment
model to account for environmentally induced variation in
recruitment with particular reference to the blue crab fishery
in Chesapeake Bay. Fisheries  Research 3: 13-21.

Turner, J. T., P. A. Tester and R. L. Ferguson. 1988. The
marine cladoceran Penilia avirostus and the "microbial loop"
of pelagic  food webs. Limnology  and Oceanography 33:
245-255.

Van Heukelem, W.  1991.  Blue Crab Callinectes sapidus In:
Habitat requirements for Chesapeake Bay  living resources.
S. L. Funderburk, J. A. Mihursky, S. J. Jordan and D. Riley
eds. Chesapeake Research Consortium,  Inc. pp 6-24.

Verity, P. G. 1991. Measurement and  simulation  of prey
uptake by marine planktonic  ciliates  fed  plastidic and
aplastidic nanoplankton. Limnology and Oceanography 36:
729-749.

Virnstein,  R. W. 1977. The importance of predarion  by
crabs  and  fishes on  benthic infauna in Chesapeake  Bay.
Ecology 58: 1199-1217.

Virnstein,  R. W.  1979. Predation on estuarine infauna:
response patterns of component  species. Estuaries 2: 69-86.

Wenner, C. A  and J. A. Musick. 1975. Food habitats and
seasonal abundance of American eel, Anguilla rostrata from
the lower Chesapeake Bay. Chesapeake Science 16:  62-66.

Wilson,  K. A, K. L  Heck, Jr. and K.  W.  Able.  1987.
Juvenile blue crab (Callinectes sapidus) survival: and elevation
of eelgrass  (Zostera marina) as refuge. Fish Bulletin 85: 53-
58.

Wilson,  K. A.,  K.  W.  Able, and  K. L. Heck, Jr. 1990a.
Predation rates on juvenile blue  crabs in estuarine nursery
habitats: evidence for the importance of macroalgae (Ulva
lactuca ). Marine Ecology Progress Series 58: 243-251.

Wilson,  K. A.,  K.  W.  Able,  and  K. L Heck, Jr. 1990b.
Habitat use by juvenile blue crabs:  a comparison among
habitats in southern New Jersey. Bulletin of Marine Science
46: 105-114.

Wylie, J.L  and D.J. Currie. 1991.  The relative importance of
bacteria and algae as food sources for crustacean zooplank-
ton. Limnology and Oceanography 36: 708-728.
 68

-------

Dennis G. Jorde
U.S. Fish & Wildlife Service
Patuxent  Wildlife  Research
Center
Laurel, Maryland
    G. Michael Haramis
U.S.  Fish & Wildlife Service
Patuxent Wildlife Research
            Center
      Laurel, Maryland
                     J.
U.S.Fish & Wildlife Service
      180 Admiral Cochrane
                         Drive
       Annapolis, Maryland
                                                 ABSTRACT
The Chesapeake Bay region is an exceptional habitat for waterbirds. These waterbirds represent primary, secondary, tertiary, and
quaternary consumers in the Bay ecosystem. The number and distribution of herbivorous waterfowl decreased at the same time
SAV (submerged aquatic vegetation or seagrasses) declined; therefore they should respond to restoration of SAV in the Bay. Moni-
toring techniques such as aerial photographic censuses of these species in SAV areas could provide meaningful comparative data.
Additional surveys of the open water areas  of the Bay are necessary to assess the populations and their distribution.
                  INTRODUCTION

The Chesapeake Bay provides  exceptional habitat for a
broad  variety of waterbirds. During pre-colonial  times,
waterbirds were attracted to  the Bay's abundant plant and
animal communities. Numbering many  millions  of birds
and consuming  hundreds  of  tons  of  aquatic  foods,
waterbirds were a significant component  of energy transfer
and nutrient cycling in the Bay. Although their populations
have greatly declined, waterbirds continue to be an impor-
tant component of the Bay's ecosystem.

           REPRESENTATIVE SPECIES IN
                 CHESAPEAKE BAY

Counting only those birds directly dependent on the waters,
over 47 species of migratory waterbirds  make the Chesa-
peake Bay  their home (Table i). Many other species of
migratory birds  are dependent on adjacent wetlands  and
shores.

The greatest number of waterfowl use the  Bay during the
fall and winter. Canada geese, canvasbacks, mallards, greater
and lesser  scaup,  bufflehead,  oldsquaw, surf scoters,
goldeneye, and  black ducks are  the  most abundant  and
important species during winter (December through March).

The Bay is  known  for its  abundant  winter waterfowl
populations, but less well known  for  the many thousands
of loons, grebes, herons, and gulls that also depend  on its
rich waters  for their winter survival. Ring-billed  gulls,
herring gulls and red-throated loons are the most abundant.
Other species of wintering nongame birds, such as bald ea-
gles, are not  as numerous, but  the welfare of the several
                    hundred birds which winter on the Bay may be critical to
                    the Atlantic coastal population.

                    After  the wintering  populations  migrate  to  northern
                    breeding  grounds  there  are  still  large  populations  of
                    waterfowl, thousands of colonial waterbirds, bald eagles and
                    osprey that depend on the rich  fishery and secluded nest
                    sites of the Bay region to  raise their young.

                                ECOSYSTEM IMPORTANCE

                    Information about the structure and temporal dynamics of
                    their  food webs is  critical for understanding waterbird
                    population dynamics and how they contribute to energy
                    flow  in the ecosystem (see Schoenly and Cohen 1991 for
                    review of food web concepts). Waterbirds are important in
                    transfer links and turnover rates of energy and nutrients in
                    the Bay during winter. Most fish and invertebrates inhabit-
                    ing the bay are preyed  on by  some birds, but the role of
                    birds  in limiting populations,  removing less fit individual
                    fish,  preying  on  competitors  of commercial  fishes,  or
                    competing with commercial fisheries is largely unknown.

                    Detailed studies of food  habits  have been  conducted on
                    only a few species and accurate population figures are diffi-
                    cult to obtain due to the migratory nature of the birds and
                    their varied and widespread distributions. The functional
                    roles of waterbirds are best defined for redheads and canvas-
                    backs  in  the  Bay (Howerter  1990, Rhodes  1989). These
                    species will be used as examples of the interaction between
                    habitat and species abundance. Redheads are dependent on
                    aquatic plant communities that contain or are dominated
                    by widgeon grass (Ruppia maritima), wild celery (Vallisneria
                    americana), sago pondweed (Potamogeton pectinatiis), eelgrass
                                                                                                               69

-------
             Table 1. Estimated populations of waterbirds in Chesapeake Bay.
 ;":-!

 1
 |
I
Species Population Estimate Survey 1
Common Loon (Gavia immei)
Red-throated Loon (Gavia stellata)
Red-necked Grebe (Podiceps grisegena)
Horned Grebe (Podiceps auritus)
Northern Gannet (Sula bassanus)
Double-crested Cormorant (Phalacrocorax auritus)
Tundra Swan (Cygnus columbianus)
Mute Swan { Cygnus oloi)
Brant (Branta bemicla)
Snow Goose (Chen caerulescens)
Canada Goose (Branta canadensis)
Green-winged Teal (Anas crecca)
American Black Duck (Anas mbripes)
Mallard (Anas platyrhynchos)
Northern Pintail (Anas acute)
Gadwall (Anas stepera)
American Wigeon (Anas americana)
Wood Duck (Aix sponsa)
Canvasback (Aythya valisineria)
Redhead (Aythya americana)
Ring-necked Duck (Aythya collaris)
Greater and Lesser Scaup (Aythya mania & A. affinis)
Common Goldeneye (Bucephala clangula)
Bufflehead (Bucephala albeola)
Ruddy Duck (Oxyura jamaicensis)
Oldsquaw (Clangula hyemalis)
Black Scoter (Melanitta nigra)
Surf Scoter (Melanitta perspicillata)
White-winged Scoter (Melanitta fusca)
Common Merganser (Mergus merganser)
Red-Breasted Merganser (Mergus serrator)
Great Blue Heron (Ardea herodias)
Little Blue Heron (Egretta caerulea)
Great Egret (Casmerodius albus)
Snowy Egret (Egretta thula)
Black-crowned Night Heron (Nycticorax nycticorax)
Bald Eagle (Haliaeetus leucocephalus)
Osprey (Pandion haliaetus)
Great Black-backed Gull (Larus marinus)
Herring Gull (Larus argentatus)
Laughing Gull (Larus atricilla)
Ring-billed Gull (Larus delawarensis)
Bonaparte's Gull (Larus Philadelphia)
Black-legged Kittiwake (Rissa tridactyla)
Common Tern (Sterna hirundo)
Least Tem (Sterna antillarum)
Royal Tem (Sterna maxima)
Black Skimmer (Rynchops niger)
4,000
12,000
1,000
2,000
5,000
13,000
30,000
2,000
5,000
5,000
300,000
2,500
27,000
60,000
2,500
2,000
6,000
100,000
60,000
3,000
10,000
80,000
50,000
60,000
42,000
100,000
26,000
115,000
17,000
6,000
40,000
17,000
300
4,000
2,000
2,500
400
4,000
6,000
75,000
abundant
125,000
5,000
1,000
6,000
1,700
6,000
1,000
1 ) Sources: a) population estimates from offshore winter surveys; b) midwinter waterfowl
c) estimates from state biologists

a
a
a
a
a
a
b~
b
b
b
b
b
b
b
b
b
c
c
b
a+b
b
a+b
a+b
a+b
a+b
a
a
a
a
a
a
c
c
c
c
c
c
c
a
a
c
a
a
a
c
c
c
c
survey or fall surveys;

Season
winter
winter
winter
winter
winter
winter
winter
winter
winter
winter
winter
winter
winter
winter
winter
winter
fall
summer
winter
winter
winter
winter
winter
winter
winter
winter
winter
winter
winter
winter
spring
summer
summer
summer
summer
summer
summer
summer
winter
winter
summer
winter
winter
winter
summer
summer
summer
summer


             (Zostera marina)  and  other  less dominant  species (e.g.
             naiads) (Haramis  1991). Currently, canvasbacks are depen-
             dent on the Bay's widely distributed Baltic clam community
             with nutrient and energy flow from the plankton to Baltic
clams to canvasbacks. However, Baird and Ulanowicz (1989)
estimated  that all waterfowl using the Bay consume about
1.5% of benthic prey production. With updated population
estimates,  we suspect waterfowl consume  up to 3.0°/o of
            70

-------
benthic prey production. The traditional diet of canvasbacks
was dominated by SAV (60%), therefore an improvement in
the community structure of SAV is expected to produce a
change in their diet favoring use of plant foods.

As  herbivores, waterfowl such as redheads transfer energy
and nutrients from  SAV  to  the Bay water column via
urinary and fecal outputs.  These outputs become available
to macro- and micro-invertebrates in the water column and
to the benthos.

Because of their  dependence on  aquatic plants, redheads,
wood ducks, and  dabbling ducks can be classified as herbi-
vores,  whereas the canvas back, scaup,  and other diving
ducks can currently be classified as epibenthic predators of
clams and other  invertebrates (refer to Hall and Raffaelli
1991 for  food web  concepts).  Bald eagles  are considered
quaternary consumers as they prey heavily on waterfowl
during the winter. Most loons, grebes, herons, egrets, cormo-
rants, gulls, terns, and osprey feed primarily on forage fishes
ranging from sculpins to menhaden making them primary
predators.

Submerged aquatic vegetation was the single most important
food resource for dabbling and diving ducks (Anatinae and
Athyini).  Annual surveys of this resource  have been con-
ducted  since  the early  1970's (Orth and  Moore  1988).
Changes in SAV in  specific areas  of the  Bay  have  been
reported for more than 40 years (e.g. Bayley a al.  1978).
Bay-wide monitoring  of SAV provides  digitized outlines of
SAV beds that can be  used as references to focus surveys for
redhead, wigeon,  and canvasback ducks. However,  not all
SAV beds will attract these species in  fall  or  winter. For
example, tubers and  winter buds of aquatic plants such as
wild celery and widgeon grass are preferred by redheads and
canvasbacks, but  horned pondweed (Zannicbellia palustru),
redhead   grass  (Potamogeton  ferfoliatus),   and  Eurasian
watermilfoil are SAV  species that are not preferred as food
or  are not  available during  winter  (Bayley et al.   1978,
Munro and Perry 1982). During autumn, wigeon often eat
SAV less desirable to other ducks, dabbling for plant leaves
floating near the water surface. However,  because wigeon
prefer the fleshy  parts of aquatic plants, winter senescence
of leaves and stems of some SAV species  limits their use by
wigeon.

          INDICATORS OF THEIR STATUS

Most waterbirds of the Chesapeake Bay are  migratory, thus
their populations  and survival  are not solely influenced by
the health of the Bay. The populations of waterbirds should
be viewed as  a suite of species because  individual  species
may be limited by factors outside the Bay region. Only with
a thorough knowledge of the birds' food habits, life history,
and  conditions they  encounter in  other areas  can  we
understand  what  fluctuations  in  waterbird  populations
mean. Interpretations of population changes must be made
at the species-specific level with  full knowledge of foraging
habits, interspecific competition, and tolerance of human
activities.

Nevertheless,  abundance  and  distribution  patterns  of
waterbirds  during winter  can provide  evidence of popu-
lation  status.  Counts of birds, such  as  the  Mid-winter
Waterfowl Survey  and nest  counts of colonial waterbirds
and raptors, do provide a consistent index. When viewed in
relation to counts throughout the Atlantic Flyway  we can
make judgements as to how the status of the birds in the
Bay relates to other areas.

Aerial  surveys  initiated in 1992 count waterbirds within
strip transects while crossing the Bay from shore to shore.
These  surveys  allow  us to estimate populations  in the
offshore waters of the Bay. Populations for many nongame
birds, seaducks, and some diving ducks presented in Table
1  were derived from  this survey. This survey should be
expanded to other seasons before accurate  estimates of the
ecological role of waterbirds in the Bay can be assessed.

Age  and  sex ratios of diving ducks  at specific wintering
areas are influenced  by flock size, competition  for  food
resources, weather conditions, and breeding  success.  For
example, during mild winters, more females and young-of-
the-year are expected to establish winter  residency rather
than continue migration to  southern winter areas. Also, if
food  resources  are  abundant  and  competition  among
individuals  is  less, more females and young should be
observed in winter flocks. Thus, monitoring age  and sex
ratios is an important component of the status of a species.

        CHOICES OF INDICATOR SPECIES

Monitoring populations in the Chesapeake Bay should be
based on the food web concept, whereby waterfowl should
be selected  as  indicators  of  the  foods they  eat.  Several
aspects of the food web must be considered when selecting
a species as an indicator of a focus resource such as  SAV,
mollusks, or other foods:  (1) the number of trophic  links
between the indicator and  the  focus species, (2) the number
of predators (both monitored and not  monitored species)
using the focus species, and (3)  sensitivity  of the indicator
species  to  reflect  changes  in  the  focus food   species.
Monitoring criteria must be carefully selected to match the
foraging  ecology of each species (Hall and Raffaelli 1991);
for example, redheads are herbivores, while  canvasbacks and
black ducks are omnivores. Submerged aquatic vegetation
responds to improved water quality  and  redheads should
respond  to increased SAV;  therefore,  annual surveys of
                                                                                                                   71

-------
redheads  for  distribution  and  population  numbers,
combined with the more intensive waterfowl surveys done
at national wildlife refuges should provide good indicators
of progress toward  restoration of SAV.

Redheads are potentially the best waterfowl indicator species
of SAV abundance and distribution in the Bay. We predict
that  redheads  will  return  to   the  Bay  in  numbers
proportional  to  restoration  of submerged aquatic plant
resources. Canvasbacks might be  a  good secondary  or
alternative indicator species because (1) they often  use the
same  SAV habitats as redheads, (2) their diet should regain
a dominance of plant  foods throughout early and  mid-
winter as SAV recovers in the Bay,  and (3)  they  can  be
censused at the same time of year as redheads by using
aerial  census  (e.g.  winter  inventory)  or photographic
techniques (e.g. Ferguson et al. 1981, Haramis  et al.  1985).

Although redheads and canvasbacks  do not breed in the
Chesapeake Bay region (Geis  1974), they are noted for their
traditional use of SAV in the Bay during fall migration and
winter (Stewart 1962). Populations of both species decreased
at the same  time that SAV  declined  throughout  the  Bay
(Munro  and Perry 1982).  Canvasbacks have been  able to
shift  their diet  from SAV to Baltic  clams (Stewart 1962,
Perry and Uhler 1988). In contrast,  redheads are one of the
most  vegetarian of waterfowl species using the Bay, and did
not shift to alternative foods following the decline  of SAV
(Haramis 1991).  Due to poor breeding conditions in the
prairie  regions,   poaching,  and  their  inflexible  food
preference,   winter  populations  of redheads   almost
disappeared with the decrease of submerged aquatic vegeta-
tion. Where once the Bay population of redheads numbered
in the tens of thousands,  now fewer than several thousand
are counted in annual winter surveys (Haramis 1991).

Black ducks  use the Chesapeake  Bay during all seasons of
the year, and prefer shallow salt marshes and brackish water
areas  for foraging and nesting (Krementz 1991). Although
this species is omnivorous, it readily forages in beds of SAV
when available (Munro and Perry 1982). Several characteris-
tics limit their value as an  indicator species: (1) winter diets
consist mostly of animal  foods obtained  from coastal wet-
lands, (2) they are difficult to census in marsh habitats, and
(3) they are  widely distributed  in  small  groups or pairs.
However, if an indicator species of breeding waterfowl is de-
sired  to monitor Bay restoration, then the black duck might
be the best choice.

American wigeon and  gadwall  are important  herbivores
during fall migration. American wigeon were once noted for
their  use of SAV in the Bay during fall migration (Stewart
1962). Some of these birds  remain in the Bay as winter
residents (Bellrose 1980), however, use of the Bay by wigeon
declined  at  the same  time as SAV.  Because wigeon are
primarily herbivores, their numbers and distribution should
change in  response to restoration of  SAV which  grows
during winter.  Therefore,  wigeon might be an excellent
choice as an indicator species of SAV restoration during the
fall migration, and  possibly as a good alternative indicator
species during winter.

The two species of birds with the largest relative increase in
populations are the mute  swan and  the mallard.  These
species are more of a sign of degradation of the Bay rather
than recovery because they readily adapt to man and highly
altered environments and  reduce diversity by  displacing
other species.  Swans  are   an exotic   species  which are
territorial and consume SAV, thus they compete with native
birds. Mallards  are abundant and breed in Bay habitats, but
should not be used as  an indicator  species because (1)
breeding mallards were likely developed  from  game farm
stock; pure  prairie mallards only winter in the  Bay, (2)
habitat use by mallards raised in  captivity most likely is not
representative of habitat use by wild birds, (3) captive-reared
and wild mallards extensively use marinas and other highly
altered habitats that would  not  be good habitat for other
birds.

Surf scoters, bufflehead,  common goldeneye,  and  scaup
occur in scattered flocks throughout the Bay during winter.
They are omnivorous, favoring animal foods. Because little
information  is  available   concerning   their  present-day
foraging ecology, the value of these diving ducks as indica-
tor species is questionable despite  relatively large popula-
tions.

    QUANTITATIVE AND QUALITATIVE GOALS

For most  waterfowl,  ideal  population  goals  would  be
represented  by the population indexes  obtained in the
1950's. Unfortunately the populations of many waterbirds
and some sea ducks are still unknown or poorly understood
and often completely lacking from the 1950's  indexes. In
addition, population goals based on  1950's  levels may be
unrealistic  for  some species such as  redheads.  Currently,
annual winter counts of redheads  range from 600 to 3000
birds for the entire  Chesapeake Bay (Haramis 1991) and the
1950's number would be 115,000 birds. The Chesapeake Bay
Waterfowl  Policy  and  Management   Plan  (CEC  1990)
established a goal for  the  year 2000 of the mean 1973-78
level or 8,200 redheads.

Qualitative  goals for  SAV dependent  waterbirds such as
redheads and wigeon  should  be based on  the geographic
distribution of recovering SAV beds  (Haramis  1991; map
38). Areas  used by redheads  throughout the Bay in past
years might provide the best locations to initially focus SAV
72

-------
•; I
  IF
restoration.  Annual  aerial and photographic censuses for
redheads at these focal sites would provide the best opportu-
nity to detect changes in SAV communities and redhead
populations.

For canvasbacks,  the 1950's goal would be 220,000 birds,
but a more realistic interim goal should be 63,000 birds by
the year 2000 (CEC 1990). Initially,  restoration of SAV in
the Bay might only redistribute the current Atlantic Flyway
population.  We expect canvasbacks  to compete with red-
heads for SAV resources, therefore mixed flocks are likely to
be observed during aerial and photographic censuses. The
historic geographic distribution of canvasbacks is similar to
redheads, and should  coincide with focal  points of SAV
restoration based on traditional redhead distributions in the
Bay. Wigeon are expected to compete for some of the same
SAV resources used by redheads, canvasbacks, and  other
waterfowl, but their ability  to eat plants less desirable to
other  waterfowl   should  reduce  competition  and  also
influence their distribution throughout the Bay.

               RECOMMENDATIONS

Monitoring
Information gained from monitoring migratory waterbirds
may provide  ambiguous  indications of Chesapeake Bay
habitat quality. Population levels are determined in part by
factors  influencing recruitment  and survival on  breeding
and  migration areas  beyond  the Chesapeake Bay region
(Haramis 1991). For example, in a particular year, popula-
tions of canvasbacks may be limited by drought or wetlands
loss  on  prairie breeding grounds, while arctic  breeding
species such as oldsquaw may have good reproduction and
large populations. Osprey abundance could be limited by
lack of fish  or heavy pesticide loads accumulated  while on
their wintering grounds in South America. Changes in bird
populations usually lag behind changes in habitat quality.
Waterbirds generally can adjust to changing habitat condi-
tions, but they may remain in traditional areas following
habitat degradation and decline of food resources. However,
waterbirds  are also highly  mobile  and able  to quickly
exploit new food resources in previously unused  or newly
created habitats. For example, when  Eurasian watermilfoil
(Myriophyllum spicatum) replaced  native SAV species on the
Susquehanna Flats  during the early  1960's,  waterfowl use
declined until native species  returned (Bayley et al  1978).

The drastic  decline in SAV food resources produced  a de-
cline in  redheads after a relatively short  lag-time, but the
response time was much longer for canvasbacks, which
changed their primary diets from SAV to animal foods. The
time for redheads to positively respond  to  restoration of
SAV in the Bay should be short, perhaps one to three years
for each restored  site, assuming that  the response involves
changes in distribution rather than recruitment of redheads
into the population.

The Mid-winter Waterfowl Survey conducted each January
along all  shorelines of the Bay should  be continued as  it
provides  a  consistent  count  of  waterfowl species  which
inhabit nearshore  areas of the Bay (see Stewart 1962 and
Nichols 1991 for review).  Although accuracy of this  survey
may suffer because of the responses of waterfowl to weather,
disturbance, or other proximate factors, it has been conduct-
ed  consistently in the  watershed  from  1957 and  provides
our only  link for comparison to the past. This survey  is
also conducted throughout the nation providing a measure
of  the proportion of waterfowl that use  the Bay in com-
parison to other major wintering habitats.

Aerial  surveys initiated in 1992 which count waterbirds in
offshore waters of the Bay within strip  transects provide
population  estimates of waterbirds. These areas  and many
of the species have been uncensused in the past. This  survey
should  be continued for a couple of  years to  determine
variability of the densities, and some form of this  survey
should be conducted in other seasons.

We recommend a coordinated SAV/waterfowl monitoring
program to  monitor waterfowl population changes and use
of SAV beds. This monitoring approach involves conduct-
ing additional waterfowl surveys  in areas where SAV beds
existed during the annual SAV survey. The SAV/waterfowl
survey should be conducted at least twice annually:  in late
October to  determine fall waterfowl use of SAV beds, and
in  mid-December  to  determine winter waterfowl use.
Because waterfowl can deplete accessible resources in SAV
beds during the earliest stages of winter, the second SAV
bed/ waterfowl survey should  not  be  conducted after
January 15th.

Variability  of  waterfowl  food   resources  are  important
monitoring  data. Estimates of long-term  food abundance,
baselines,  and estimates of short-term variations are impor-
tant factors to understand  waterfowl  abundances. This
information can be used  as  inputs for various  ecosystem
models of the Bay.

Another potentially important consideration is the effect of
toxic  substances.  Contaminants accumulated   in  food
resources  might be harmful to ducks and make  it hard to
determine  how   they   respond  to   SAV  restoration.
Environmental contaminants  could  bias  interpretation of
monitoring  data.

Modeling
Ecosystem models  should  be developed and evaluated based
on   tests  of  hypotheses   and  predictions  (Wetzel and
                                                                                                                         73

-------
Hopkinson  1990). Generally, sufficient information  to
develop even simple food-web models related  to waterbird
use (foraging ecology and food bases) is available only for
redheads, canvasbacks,  and black ducks. Currently, con-
ceptual models of the Bay ecosystem include  waterfowl as
components of SAV and benthos subsystem models (WetZel
and Hopkinson  1990). Perhaps a more direct and  useful
approach might be based on energetics or carbon transfer
(Baird and Ulanowicz 1989).


Management
The focus of  management  goals  and  field  monitoring
efforts should be to  provide  the required food resources
needed to maintain desired populations. The availability of
food resources must be monitored annually and compared
with  desired food abundances.  Habitat restoration and
management efforts should continue until average long-term
stability  of food resources  and waterfowl populations is
reached and maintained.

Waterbird  abundance  can  be  related  to  current and
potential Bay management strategies. One approach is to
estimate  what historical food resources and corresponding
waterfowl populations were supported by the Chesapeake
Bay (e.g. Bayley  et al. 1978),  then  decide what waterfowl
species  and  how  many  individuals  of  each   species
(population  size) the  Chesapeake  Bay  can  consistently
support for a given period of time.

Restoration of Bay water quality should  restore preferred
waterbird foods and  increase  use by wintering birds. The
nutritional quality of foods is also  an important factor,
especially when present foods are neither the preferred nor
the historical diet of many species. Management programs
to  restore  specific   species  of  SAV  need   to  consider
information  about physiological  and  ecological  require-
ments of birds (e.g. Korschgen and Green 1988, Kahl 1991).


Disturbance  of both  wintering and nesting  birds is  an
important factor  in their ecology. Disturbance of wintering
birds can reduce their fitness by causing them to fly and
expend  energy   needed  for  survival  or  migration.
Disturbance of nesting birds may cause adults to abandon
nests or  young and eggs  to  fall from nests or  be lost to
predators.

Disturbance  should  be  limited when  possible.  A  few
possibilities are:  limiting  access to  islands during  critical
periods, establishing buffers around sensitive nesting areas,
instituting open  water  sanctuary   areas  with  restricted
hunting,  and  limiting  boating speeds  for areas  with
exceptionally large concentrations of diving ducks.
                    REFERENCES

Baird,  D.  and  R.  E. Ulanowicz.  1989.  The  seasonal
dynamics  of the  Chesapeake  Bay ecosystem. Ecological
Monographs 59: 329-364.

Bayley, S., V. D. Stotts, P.  F. Springer, and J. Steenis. 1978.
Changes in submerged aquatic  macrophyte populations of
Chesapeake Bay, 1958-1975. Estuaries  1: 171-182.

Bellrose,  P. C.  1980. Ducks, geese, and swans of North
America. Stackpole Books, H-arrisburg, PA.

Chesapeake  Executive  Council.   1990.  Chesapeake   Bay
Waterfowl Policy and Management Plan. Annapolis, MD.

Ferguson, E. L, D. G. Jorde, and J. J. Sease. 1981. Use of 35-
mm color aerial photography to  acquire mallard sex  ratio
data. Photogrammetric Eng.  Remote Sensing 47: 823-827.

Geis,  A.  D.  1974.  Breeding  and  wintering  areas  of
canvasbacks harvested  in various  stages  and  provinces.
USDI, FWS Special Scientific Report,  Wildlife 185.

Hall, S. J. and D. Raffaelli. 1991. Foodweb patterns:  lessons
from  species-rich web. Journal of Animal Ecology 60: 823-
842.

Haramis, G. M., J.  R. Goldsberry,  D. G. McAuley, and E. L.
Derleth. 1985. An aerial photographic  census of Chesapeake
Bay and North Carolina  canvasbacks. Journal of Wildlife
Management 49: 449^154.

Haramis, G. M. 1991. Redhead. Pages  18-1 to 18-10 in S. L.
Funderburk, S. J. Jordan, J. A. Mihursky, and D. Riley, eds.
Habitat requirements for  Chesapeake  Bay living resources.
Chesapeake Research Consortium, Inc., Solomons, MD.

Howerter, D. W.  1990. Movements  and bioenergetics of
canvasbacks wintering  in  the upper Chesapeake Bay.  M.S.
Thesis. Virginia Polytechnic Institute  and State University,
Blacksburg.

Kahl, R.  1991. Restoration  of  canvasback  migrational
staging  habitat in Wisconsin.  Wisconsin  Department of
Natural Resources  Technical Bulletin  172.

Korschgen, C. E.  and W. L Green.  1988. American wild
celery (Vallisneria  americana): ecological  consideration for
restoration. U.S.D.A. Fish and Wildlife Technical Report.

Krementz, D. G. 1991. American  black duck. Pages  16-1 to
16-7 in S.  L. Funderburk,  S. J. Jordan, J. A. Mihursky, and
D.  Riley,  eds. Habitat requirements  for Chesapeake  Bay
74

-------
lal
of
living  resources.  Chesapeake  Research  Consortium,  Inc.,
Solomons,  MD.

Munro, R.  E.  and M. C. Perry.  1982.  Distribution and
abundance of waterfowl and submerged aquatic vegetation
in Chesapeake Bay. EPA 600/3-82-082.

Nichols, J.  D. 1991.  Extensive monitoring programmes
viewed as long-term population  studies: the case of North
American waterfowl. Ibis 133:  89-98.

Orth,  R. J. and  K. A. Moore.  1988. Submerged aquatic
vegetation  in  the  Chesapeake Bay; a barometer of Bay
health. Pages 619-629 in M. P.  Lynch and E. C. Krome, eds.
Understanding the estuary: advances in  Chesapeake Bay
research. Chesapeake  Research Consortium Publ.  129,
Solomons,  MD.

Perry,  M.  C.  and  F.  M. Uhler.  1988.  Food habits and
distribution of wintering canvasbacks, Aythya. valisneria, on
Chesapeake Bay. Estuaries 11:  57-67.
Rhodes,  W.  E.  1989.  Habitat  use  by  juvenile  female
canvasbacks wintering on the upper Chesapeake Bay. M.S.
Thesis. Virginia Polytechnic Institute and  State University,
Blacksburg.
Schoenly, K. and J. E. Cohen. 1991. Temporal variation in
food  web  structure:  16   empirical  cases.  Ecological
Monographs 61: 267-298.
                                                                             Stewart, R.  E.  1962. Waterfowl populations in the upper
                                                                             Chesapeake Region. U. S. Fish and Wildlife Service Special
                                                                             Scientific  Report on Wildlife No.  65.
                                                                             Wetzel, R.  L.  and  C. S. Hopkinson, Jr.  1990. Coastal
                                                                             ecosystem  models   and  the  Chesapeake  Bay  Program;
                                                                             philosophy, background,  and status. Pages 7 - 23 in  M.
                                                                             Haire and E. C. Krome, eds. Perspective on the Chesapeake
                                                                             Bay, 1990: advances in estuarine sciences. Chesapeake Bay
                                                                             Consortium, Gloucester Point, VA.
      -5< f-
      a I-
                                                                                                                                 75

-------
1
1

-------
                          AQUATIC
Robert J. Orth
Virginia Institute of Marine Science
School of Marine Science
College of William and Mary
Gloucester Point, Virginia
                            William  C. Dennison
        Horn Point Environmental Laboratory
                          University of Maryland
                        Center for Estumrine
                           Environmental
                            Cambridge, Maryland
                  INTRODUCTION

One of the major factors contributing to the high produc-
tivity of Chesapeake Bay has been the historical abundance
of submersed aquatic vegetation (SAV). Submersed  aquatic
vegetation are rooted  flowering plants that have colonized
soft sediment  habitats  in coastal  and  estuarine  areas
throughout  the world.  In Chesapeake Bay, seagrasses in
saline regions and freshwater angiosperms that have colo-
nized lower salinity portions  of the  estuary constitute a
diverse community (Stevenson and Confer 1978, Orth and
Moore 1984).

A baywide decline  of all  SAV  species in Chesapeake Bay
began in the late 1960's and early 1970's (Orth and Moore
1983). This SAV decline was related to increasing amounts
of  nutrients and  sediments in  the  Bay resulting  from
development of the Bay's shoreline and watershed (Kemp e,t
at.  1983).

                       SPECIES

There are approximately  24 species of SAV  reported in
Chesapeake  Bay with  twelve commonly reported (Table 1)
(Orth et al. 1989, 1991;  Orth  and  Nowak  1990).  The
presence of a  species in  a particular salinity regime  is
dependent on its salinity tolerance (Table 1). Zostera marina
is the only  true seagrass, whereas two species  in the tidal
freshwater and oligohaline  areas,  Hydrilla verticillata and
Myriophyllum spicatum,  are  exotics. Hydrilla  has  rapidly
spread in the Potomac River since it was first reported in
1983, and is abundant  principally in the tidal freshwater
and oligohaline areas of this river. Hydrilla  has also been
found less  abundantly on the  Susquehanna Flats.  Ruppia
maritima, a species with the widest salinity range, has shown
a significant resurgence in the mid-1980's in many sections
of the middle bay, and in the Rappahannock River.

             ECOSYSTEM IMPORTANCE

Submersed aquatic vegetation  provide food  for waterfowl
and are critical habitat for shellfish and fmfish. It supports
some of the  densest and most diverse  benthic  faunal
communities in the bay. Submersed aquatic vegetation also
affect nutrient cycling, sediment stability and water turbidity
(Kemp et al. 1984, Thayer et al. 1984; also reviewed  in
McRoy and Helfferich 1977, Phillips and McRoy 1980, and
Larkum et al. 1990).

Table 1. Species of SAV found in the different salinity regimes of
the  Chesapeake Bay and tributaries  {from Orth et al.  1991).
Species which are abundant in more than one salinity regime are
listed appropriately.
  Salinity Regime/Species

  Polyhaline
  Zostera marina
  Ruppia maritima
  Zannichelia palustris

  Mesohaline
  Zostera marina
  Ruppia maritima
  Zannichelia palustris
  Potamogeton pectinatus
  Potamogeton perfoliatus
  Myriophyllum spicatum
  Vallisneria americana

  Oligohaline/Freshwater
  Ruppia maritima
  Potamogeton pectinatus
  Potamogeton perfoliatus
  Myriophyllum spicatum
  Vallisneria americana
  Heteranthera dubia
  Hydrilla verticillata
  Elodea canadensis
  Ceratophyllum demersum
  A/a/as guadllupensis
  Zannichelia palustris
                                   Common Name
eelgrass
widgeongrass
horned pondweed
eelgrass
widgeongrass
horned pondweed
sago pondweed
redhead grass
water milfoil
wild celery
widgeongrass
sago pondweed
redhead grass
water milfoil
wild celery
water stargrass
hydrilla
common elodea
coontail
southern naiad
horned pondweed
              INDICATORS OF STRESS

A conceptual model of the interactions and interdependence
of the SAV habitat requirements (Fig. 1) illustrates the water
quality  parameters that influence SAV distribution and
abundance. A wealth of scientific studies from around the
                                                                                                                77

-------
Figure  1.  Availability of light for SAV is determined by light
attenuation  processes. Water column attenuation, measured as
light attenuation coefficient (Ka), results from absorption and scatter
of light by particles in the water (phytoplankton, measured as chlo-
rophyll a; total organic and inorganic  particles, measured as total
suspended solids) and by absorption  of light by water itself. Leaf
surface attenuation, largely due to algal epiphytes growing on SAV
leaf surfaces, also contributes  to light attenuation. Dissolved
inorganic nutrients (DIN = dissolved inorganic nitrogen, DIP = dis-
solved inorganic phosphorus) contribute to phytoplankton  and
epiphyte components  of overall light attenuation, and epiphyte
grazers control accumulation of epiphytes.
world have established  the importance of light availability
as the major environmental factor controlling SAV distribu-
tion, growth  and survival (Dennison 1987, Kenworthy and
Haunert 1991). The primary environmental factors  contrib-
uting to light attenuation are used to formulate SAV habitat
requirements: light attenuation coefficient (Kd), chlorophyll
a, total suspended  solids, dissolved  inorganic  nitrogen
(DIN) and dissolved inorganic phosphorus (DIP).

The minimum light requirement of a particular SAV species
determines the maximum water depth for survival. This can
be depicted  graphically  as the  intersection of the light
intensity vs.  depth curve with  the minimum light require-
ment value  (Fig.2) Light is attenuated exponentially with
water depth  (Fig. 2  right side). The  minimum  light  re-
quirement of a  particular  SAV species,  as a  percent  of
                                                                                              Seagrass Minimum
                                                                                              Light Requirement
                                                                                     Secchidepth
                                                                    Maximum depth of
                                                                    Seagrass survival
                                                                 Figure 2. The interrelationships between light attenuation, SAV
                                                                 minimum light requirement, Secchi depth and the maximum depth
                                                                 of SAV survival  depicted schematically. The intersection of the
                                                                 minimum light requirement and light attenuation curve determines
                                                                 the maximum depth of SAV survival.
incident light,  intersects the light curve to give a predicted
maximum depth of SAV survival for that species (Fig. 2, left
side). Knowledge of any 2 of the 3 unknowns (average light
attenuation  coefficient (Kd), minimum light  requirement,
and maximum depth of seagrass survival) allows determina-
tion of the remaining unknown. In this manner, SAV depth
penetration is used as  an integrating "light meter" to assess
light regimes on appropriate  temporal and spatial scales
without intensive sampling programs  (Kautsky a tf/. 1986).
Secchi depth, a long standing  field measurement of light
attenuation, can be used to determine the  light attenuation
coefficient  (Kd)  by a conversion  factor  established for
Chesapeake  Bay (Batiuk et a.1.  1992). Hence, Secchi depth
measurements, along  with  SAV minimum  light require-
ments, can  be  used to determine the maximum depth of
SAV survival.

Empirical relationships between water quality characteristics
and SAV distributions  provided the means of defining
requirements   for  seagrass  survival.   Submersed  aquatic
vegetation habitat requirements were  formulated  by a)
determining SAV distributions by transplant survival and
bay-wide distributional surveys, b) measuring water quality
characteristics  along  large  scale transects  that  spanned
vegetated  and non-vegetated regions, c) combining distrib-
utional data and water quality levels (as in Fig. 3) to estab-
lish minimum water  quality that supports SAV survival.
This type of analysis (referred to as correspondence analysis)
was  strengthened  by  factors common to  each of the case
studies. Field data was collected over several years (almost a
78

-------
Table 2. Chesapeake Bay seagrass habitat requirements. For each parameter, the maximum growing season median value that correlated with
seagrass survival is given for each salinity regime. Growing season defined as April-October, except for polyhaline (March-November). Salinity
regimes are defined as tidal fresh = 0 - 0.5%, oligohaline = 0.5 - 5%, mesohaline = 5 -18%, polyhaline = 18+%.


Salinity
Regime
Tidal
Freshwater
Oligohaline
Mesohaline
Polyhaline
Light
Attenuation
Coefficient
(Kd; nv1)
2.0

2.0
1.5
1.5
Total
Suspended
Solids
(mg/I)
15

15
15
15
Chlorophyll
a
(ug/i)

15

15
15
15
Dissolved
Inorganic
Nitrogen
(mg/I)
_

-
<0.15
<0.15
Dissolved
Inorganic
Phosphorus
(mg/I)
<0.02

<0.02
<0.01
<0.02
FIgyre 3. Three dimensional comparisons of May-October median
light attenuation coefficient, total suspended solids and chlorophyll
a concentrations at the Choptank River stations for 1986-1989.
Plus = persistent SAV; flag = fluctuating SAV; circle = no SAV.

decade in the Potomac  River) in varying meteorologic and
hydrologic conditions by different investigators. Distribu-
tions of SAV in four case studies (Susquehanna Flats, upper
Potomac River, Choptank River, and York River) across all
salinity regimes  were responsive to the five water quality
parameters  used  to  develop  habitat  requirements.  In
addition,  inter-annual  changes  in  water quality led to
changes in  seagrass distribution and abundance in each
region that were consistent with habitat requirements.

The diversity of SAV communities throughout Chesapeake
Bay,  with its wide  salinity range, has led to the establish-
ment of separate  habitat requirements, based on  salinity
regime. Water  quality  conditions  sufficient to support
survival, growth, and reproduction of SAV to water depths
of one meter  are used as SAV habitat requirements (Table
2).  For SAV  to  survive  to  one  meter,  light attenuation
coefficients <2 m"'  for  tidal  fresh and oligohaline regions
and <1.5  m4  for mesohaline and polyhaline regions were
needed. Total  suspended solids (< 15 mg/1) and chlorophyll
a (< 15 ug/1) values were consistent for all regions.

However,   habitat  requirements for  dissolved  inorganic
nitrogen (DIN) and phosphorus (DIP) varied substantially
between salinity regimes. In tidal freshwater and oligohaline
regions, SAV survive episodic and chronic high DIN, conse-
quently habitat requirements for DIN  were not determined
for  these  regions.  In  contrast, maximum  DIN  concen-
trations of 0.15 mg/1 were established for mesohaline and
polyhaline regions.

The SAV  habitat requirement  for DIP was <0.02 mg/1 for
all   regions   except  mesohaline   regions   (<0.01  mg/1).
Differences in nutrient habitat requirements  in different
regions of Chesapeake Bay are consistent with  observations
from a  variety  of estuaries  that  shifts in  the relative
importance of phosphorus vs. nitrogen as limiting factors
occur (Valiela  1984).

Habitat  requirements  for  SAV  represent the absolute
minimum water quality characteristics necessary to sustain
plants  in  shallow water. As such, exceeding any of the five
water quality  characteristics will seriously compromise the
chances of SAV survival.  Improvements in water clarity to
achieve greater depth penetration of SAV would not only
increase depth penetration, but also increase seagrass density
and  biomass.  In  addition, improvements of water quality
beyond  the  habitat  requirements   could  lead  to  the
                                                                                                                     79

-------
s
maintenance or reestablishment of a diverse population of
native SAV species.  Habitat requirements for SAV provide
a guideline for  mitigation efforts involving transplants. If
SAV habitat requirements are not present,  reestablishment
of SAV communities via  transplant  efforts would be futile.

The empirical  approach used  here allows  for  predictive
capacity without detailed knowledge of the precise nature
of  SAV/water  quality  interactions.  Since SAV  are  disap-
pearing rapidly  on a global scale, there is a need  to provide
guidelines on water  quality before a more complete under-
standing of the complex  ecological  interactions is reached.
The application of a habitat requirements approach to other
ecosystems should be explored. Submersed aquatic vegeta-
tion beds are convenient "light meters," integrating water
clarity of coastal waters over appropriate time scales. Other
organisms also  possess critical thresholds for a  variety of
environmental factors that can be used to establish  habitat
requirements. This approach has the important  advantage
of  low technology,  high  information yield that can  be
employed in a variety of settings.

                RECOMMENDATIONS

Monitoring
Monitoring of SAV  distribution and abundance is critical
in order to assess the success of nutrient reduction strategies
currently  in place,  or proposed  for  implementation,  in
Chesapeake Bay. This  monitoring program should consist
of several elements:

1. An  annual survey of SAV distribution and abundance
using current aerial photographic techniques;

2. Groundtruth surveys of citizens  and scientists conducted
concurrently with the  aerial survey  to provide confirming
documentation on the presence of SAV and species  found;

3. Monitoring of water quality  at selected  stations  in  the
shallows where SAV grows to complement the mid-channel
monitoring stations; and,

4. Regular evaluation of the trends in SAV abundance and
water quality and, in particular, assessment of current status
in relation to restoration targets  established in the SAV
Technical Synthesis.

Research
The following areas should be considered for future research
with SAV:

1. Research into transplanting SAV to (a) refine  specific
habitat requirements of individual species of SAV both for
long term persistence and/or recolonization and restoration
 of SAV populations, and (b) quantify rates of revegetation
 into unvegetated areas.

 2.  Research   to   improve  our   understanding  of  the
 relationships between SAV and other important Chesapeake
 Bay species, in particular waterfowl, fish, and shellfish. In
 addition, research needs to address the  interactions  and
 interrelationships between SAV and other habitats, such as
 oyster reefs and unvegetated sand flats.

 3.  Research  on the  effects of eutrophication,  sediment
 loading, toxics, and natural purturbations on growth  and
 survival of SAV, in particular the lag time, or delay in SAV
 response, to changes in ambient light regimes. In addition,
 duration   and  timing  of  purturbations  needs  to  be
 incorporated into these strategies.

 4. Research to develop a more complete knowledge of the
 sources  and   causes  of  the   various   light  attenuation
 components.

 5. Research on the epiphyte component of light attenuation,
 particularly with regard to nutrient enrichments.

 6.  Research  on  how loading rates  affect  the habitat
 requirements developed in the Technical Synthesis (Batuik
 etal. 1992).

Management
Because   SAV  are  most   affected  by  water  quality,
management efforts  must  be  directed  towards  attaining
water quality values within their habitat requirements. Point
sources of nutrient inputs are  the  easiest to control but it
is critical  to understand how loading rates are translated to
actual concentrations observed in the field. More difficult
is the  control of non-point sources, both as direct runoff,
but  also   as  atmospheric  deposition  and  groundwater
infiltration.

Existing SAV beds should receive the highest protection by
all governmental agencies as these represent areas that could
serve as  sources of propagules for natural and artificial
restoration. In  addition, potential habitat (habitat that has
either  historically supported SAV or habitat defined within
the 2 meter contour of the bay) should receive protection.

Modeling
Current  seagrass models  and  efforts  to use models  as a
research  tool   are  far from complete relative to  under-
standing the current or historic distribution and abundance
of seagrasses.  Models that  focus on  seagrasses  (or  more
generally submersed aquatic vegetation) have not yet been
developed and  implemented for the explicit purpose of pre-
dicting plant  response  to  environmental variables.   The
80

-------
environmental controls of seagrass growth and/or survival
at the community level of ecological organization  remain
for all practical purposes a planning tool for basic research
(Kemp a al. 1983, Wetzel and Neckles 1986). Other  models
have been developed that address seagrasses but they have
employed  conceptual   and/or  mathematical  structures,
neither  appropriate for nor  designed  for  predicting the
environmental effects (e.g. light attenuation, nutrients, and
grazing  impacts) on the larger issues of community survival
and longevity (Short 1980). Other models are published that
address  community productivity, plant growth, and nutrient
interactions,  and,  in a  general  sense, the  relationships
between certain environmental variables, and  plant growth
and  depth  distribution (Verhagen and Nienhuis  1983,
Zimmerman et al.  1987).

                      Objectives

1. TO  EFFECTIVELY PREDICT SAV  RESPONSE  TO  ENVI-
RONMENTAL   PARAMETERS,   PARTICULARLY   THE  WATER
QUALITY PARAMETERS USED  AS THE SAV INDICATORS OF
STRESS.

2. TO DEVELOP COMMUNITY AND ECOSYSTEM LEVEL MODELS
TO PREDICT  ENVIRONMENTAL EFFECTS ON  COMMUNITY
SURVIVAL AND LONGEVITY.

3. TO  INTEGRATE  COMPONENTS OF LIGHT ATTENUATION,
EPIPHYTE  LIGHT  ATTENUATION,   AND PLANT/SEDIMENT
INTERACTIONS INTO MODELS  OF SAV.

Habitat
Because of the  ecosystem importance of SAV and their
sensitivity to water quality, existing SAV habitat must be
protected,  as  well as  restored  in those  areas that  are
currently devoid of any SAV. Areas with marginal growth
should be enhanced. Restoration targets for species diversity
and abundance can be used as a goal to assess the success or
failure of efforts to clean up  the Chesapeake  Bay. A  tiered
set of SAV distribution restoration targets established in the
SAV Technical  Synthesis (Batiuk  et  al.  in press)  gives
management agencies a quantitative measure  of change in
SAV distribution at different levels in response to the imple-
mentation of Chesapeake Bay restoration strategies (e.g.
reducing nutrients by 40°/o).

                    REFERENCES

Batiuk, R.A.,  R.J.  Orth, K.A. Moore, W.C. Dennison, J.C.
Stevenson,  L.W.  Staver, V. Carter,  N.B.  Rybicki, R.E.
Hickman,  S. Kollar,  S.  Bieber, and P. Heasly.  1992.
Chesapeake Bay submerged aquatic vegetation habitat
requirements and restoration targets: A technical synthesis.
Chesapeake  Bay Program.  CBP/TRS 83/92.  Annapolis,
Maryland.
Dennison,  W.C.  1987.  Effects  of  light  on  seagrass
photosynthesis, growth and  depth  distribution. Aquatic
Botany 27: 15-26.

Kautsky, N., H. Kautsky, U. Katusky, and M. Waern. 1986.
Decreased depth  penetration  of Fucus  vesiculosus (L.) since
the 1940's indicates eutrophication of the Baltic Sea. Marine
Ecology Progress  Series 28: 1-8.

Kemp, W.M., W.R. Boynton, R.R. Twilley, J.C. Stevenson,
and J.C. Means.  1983. The. decline of submerged vascular
plants  in  upper  Chesapeake  Bay:  Summary of  results
concerning  possible  causes.  Marine Technology Society
Journal  17: 78-89.

Kemp, W.M., W.R. Boynton, R.R. Twilley, J.C. Stevenson,
and  LG. Ward.  1984,  Influences of  submerged vascular
plants on ecological  processes  in upper Chesapeake Bay.
Pages 367-394 in  V.S. Kennedy (ed.)  Estuaries  as  Filters.
Academic Press, New York.

Kenworthy, W.J., and D.E. Haunert, eds.  1991. The  light
requirements of seagrasses: Proceedings of a workshop to
examine the capability of water quality criteria, standards
and  monitoring  programs to  protect  seagrasses. NOAA
Technical Memorandum NMFS-SERC-287.

Larkum, A.W.D.,  A.J. McComb, and  S.A. Shepherd, eds.
1989. Biology of Seagrasses: A Treatise on the Biology of
Seagrasses With Special Reference to the Australian Region.
Elsevier, Amsterdam.

McRoy,  C.P.,  and   C.   Helfferich,  eds.  1977. Seagrass
Ecosystems: A Scientific Perspective.  Dekker, New York.

Orth, R.J., and  K.A. Moore.  1983.  Chesapeake Bay: An
unprecedented  decline  in submerged  aquatic  vegetation.
Science  222: 51-53.

Orth, R.J, J.F. Nowak, A.A. Frisch, K. Kiley, and J. Whiting.
1991. Distribution of submerged aquatic vegetation in the
Chesapeake Bay and  tributaries and Chincoteague Bay -
1990. U.S. EPA, Chesapeake Bay Program, Annapolis, MD.

Orth, R.J., A. A. Frisch, J.F. Nowak, and K. A. Moore. 1989.
Distribution  of  submerged   aquatic  vegetation  in  the
Chesapeake Bay and  tributaries and Chincoteague Bay -
1987. U.S. EPA, Chesapeake Bay Program, Annapolis, MD.
247 pp.

Orth, R.J. and J.F. Nowak. 1990. Distribution of submerged
aquatic  vegetation in the Chesapeake  Bay and  tributaries
and Chincoteague Bay -  1990. U.S.  EPA, Chesapeake Bay
Program, Annapolis, MD. 249 pp.
                                                                                                                  81

-------
Phillips, R.C., arid C.P. McRoy, eds. 1980. A Handbook of
Seagrass Biology: An Ecosystem Perspective. Garland, New
York.

Stevenson, J.C.,  and N.M.  Confer.   1978.  Summary of
available  information  on  Chesapeake  Bay  submerged
vegetation.  U.S.  Fish  and  Wildlife  Service Office  of
Biological Services FWS/OBS-78/66.

Short, F.  T. 1980. A simulation model  of the seagrass
production  system.pp. 277-295.In: R. C. Phillips and C. P.
Me Roy (eds.).Handbook of seagrass biology:  An ecosystem
perspective.Garland Press, NY.

Thayer,   G.  W.,  W.   J.   Kenworthy,  and   M.  S.
Fonseca.1984.The  ecology  of eelgrass meadows of the
Atlantic coast: A community profile. U. S. Fish and Wildlife
ServiceFWS/OBS-84/02. 147 pp.
Valiela, I.  1984. Marine Ecological  Processes.  Springer-
Verlag, New York.

Verhagen, J. H. G. and P. H. Nienhuis. 1983. A simulation
model of  production,  seasonal changes  in biomass  and
distribution of eelgrass (Zostera marina)  in  Lake Greve-
lingen.Marine Ecology Progress Series 10:  187-195.

Wetzel, R.  L and H. A. Neckles. 1986. A  model of Zostera
marina L. photosynthesis and growth: simulated  effects of
selected physical-chemical variables and biological interac-
tions. Aquatic Botany 26: 307-323.

Zimmerman, R. C., R. D. Smith, and R. S. Alberte. 1987.1s
growth of eelgrass nitrogen limitedPA numerical simulation
of the effects of light and nitrogen on the  growth  dynamics
of Zostera  marina. Marine  Ecology Progress Series 41:  167-
176.
82

-------

J. Court Stevenson
University of Maryland
Horn Point Environmental Laboratory
Cambridge,  Maryland
                                 Edward Pendleton
                      U.S.Fish  & Wildlife Service
                    180 Admiral Cochrane Drive
                              Annapolis, Maryland
                   INTRODUCTION

Sandwiched between the low tide line of Chesapeake Bay
and the uplands, lies a spectrum of wetland communities
which mediate exchanges from one system  to  the other.
These wetland  communities can  be defined  technically in
terms of  hydrology, soil type and plant  species  but are
generally systems in which the substrate is saturated for a
portion of time which creates periodic anaerobic conditions
in the root zone. Since comparatively few plants are adapted
to low or no oxygen in the root zone, distinctive  communi-
ties develop depending on the degree and periodicity of soil
saturation. Because wetland plants have varying  tolerances
to anaerobic conditions (and salinity), a range of species can
dominate, depending on the micro-climate, but as  a whole
they harbor a rich diversity of consumer species which are
an essential ingredient in the image of a healthy Chesapeake
ecosystem.

These animals  include an array of migrants from warblers
to waterfowl as well as many species of fish (eels, killifish,
mummichogs,  pipefish,  etc.).  In  addition, there are both
conspicuous invertebrates (blue crabs) and inconspicuous
ones  (amphipods and copepods) which have direct connec-
tions with harvestable resources in the open bay.  Moreover,
a few marsh mammals (muskrat, otter, and deer) have long
been  important for both commercial hunting and sports-
men. Wetlands are also enjoyed by local residents  who  go
in  for  "frogging"  and/or  "turkelling"  (hunting  turtles-
snappers mostly, but terrapins can often be found  in large
quantities in marsh embayments  as well),

In  addition to their functions as regards  habitat  (not to
mention water quality, and landscape hydrology discussed
later), the wetlands contribute variety and interest as well as
an  aesthetic character to  the rim of the Bay. If for  nothing
else, these systems need to be protected as  essential habitat
for the variety of species which use them. Indeed, since they
are often the last resort of many  species whose habitat was
destroyed with the encroachment of development, wetlands
were among the first components of the Chesapeake System
to  receive regulatory protection.  Public support for these
resources  is attested to  by legislation afforded them.  In
Maryland, laws were passed in the early 1970's for protec-
tion of tidal marshes and in the late 1980's the non-tidal
wetland systems were also included.

             REPRESENTATIVE SPECIES

Wetlands can be classified in several ways depending on the
issues of concern - floristics, geomorphology, etc. (Stevenson
a al. 1986). A general scheme which  has been  used  in
mapping in the Chesapeake region (and elsewhere) by the
U.S. Fish and Wildlife Service to identify long term trends
(Tiner 1987) is  as follows:
Wetland Type
Tidal Flats and
Beaches
Coastal
Marshes
Freshwater
Emergent
Wetlands
Shrub
Wetlands
Forested
Wetlands
Freshwater
Ponds
Representative
Plant Species
Occasional Ulva &
Zannichellia palustris
High Salinity:
Spartina altemiflora
Spartina patens
Low Salinity:
Scirpus olneyii
Spartina cynosuroides
Tidal Fresh:
Pontederia cordate
Zizania aquatica
Scirpus validus
Bidens cemua
Chelone glabra
Cicuta maculata
Hypericum virgicum
Justicia arnericana
Lycopus yirginicus
Mimulus ringens
Typha latifolia
Alnus serrulata
Asimina triloba
Cephalanthus occidentalis
Rhododendron viscosum
Myrica cerifera
Acer rubrum
Chamaecyparis thyoides
Betula nigra
Fraxinus pensylvanica
Larix larcina
Nyssa sylvatica
Taxodium distichum
Nuphar luteum
Myriophyllum spicatum
Lemna minor
Current %
Acreage Change
84,500
                                        134,500  -8.5
                                        103,500
                                        152,000  -6.0
                                        657,700
90,700   +170
The cumulative acreage of these systems in the Chesapeake
drainage basin (Total= 41 million acres), is estimated at just
                                                                                                                   83

-------
1
            less than one and a quarter million acres by the U.S.  Fish
            and  Wildlife Service  (Tiner  1987),  or 3% of the total
            watershed.  However, in all likelihood, due both to underes-
            timation of forested wetlands detectable in the aerial photo-
            graphs and the  expanded definition of non-tidal  wetlands
            (now being debated), a larger percentage (more in the range
            of 5%) of the  watershed is  undoubtedly wetlands.  The
            percentage change in the table above is over a  thirty  year
            period from the 1950's to the 1980's and reflects consider-
            able loss of wetlands  both to apparent sea-level  rise  and
            development. The highest amount of loss (8.5%) is in tidal
            coastal wetlands, but for the same reasons cited above for
            non-tidal wetlands the percentage loss may be less  than 6°/o
            cited  above.

                   IMPORTANCE TO THE CHESAPEAKE
                                 ECOSYSTEM

            There is considerable evidence (Mitsch and Gosselink 1986,
            LeBaugh 1986, Gehrels and Mulamouttil 1989, Athanas and
            Stevenson 1991) that a variety of wetland systems can act as
            significant  sinks in the landscape;  particularly in regard to
            nutrients (Boyd  1969) but also in terms of metals which are
            attached to sediments (Simpson et al, 1983). As Gosselink et
            al. (1974) suggest, "detailed analysis of waste assimilation
            shows that...marshes have a tremendous capacity  for tertiary
            treatment of nutrients, especially phosphorus." In addition,
            because of the alternating redox conditions in wetland soils,
            denitrification can cause a release of nitrogen (N)  into  the
            atmosphere. When the reduction of nitrate is complete, and
            mostly N2 is released,  no environmental  damage occurs,
            which greatly enhances their value. However not all of this
            is positive. If denitrification is incomplete, N2O emissions
            can  result  (Seitzinger   1988)  which  contributes  to   the
            greenhouse effect. This negative contribution might be even
            more problematic in view of the fact that several wetlands
            in the Chesapeake region have significant methane produc-
            tion (Harriss et al. 1985, Bartlett et al. 1987) -another potent
            greenhouse gas.


            On the other hand, coastal marshes, have also been consid-
            ered  as  sources of nutrients and energy  subsidies   for
            shallower  coastal waters (Odum 1961), "outwelling" large
            quantities of detrital materials. Nutrient exchanges studies
            in the Chesapeake (e.g. Heinle and Flemer  1976, Stevenson
            et al.  1977, Jordan et  al. 1983,  Wolaver et al.  1983) have
            indicated   varying   degrees of nutrient  transformation,
            retention and loss in a variety of wetland systems. Jordan et
            al.  (1983)  have emphasized  the  primary  role  of tidal
            marshes at  Rhode  River (on  the  western shore of Chesa-
            peake Bay) was  in their ability to  transform  particulate to
            dissolved  nutrients-rather  than  nutrient retention  and
            release. Jordan and  Correll (1985) have concluded that a
            little less than half of the nutrient export they observe at
Rhode River is due to tidal pumping- seepage of interstitial
water out of the sediments at low tide.

In  non-tidal  wetlands,  orthophosphorus  (bioavailable
phosphorus) has also  been  shown to be exported during
fall; especially in systems which  have reached  equilibrium
(Richardson 1985). Although perhaps not as significant as
burial or atmospheric losses; the time delay,  which these
wetlands offer, still benefits  the Bay in that the release of P
does not occur in spring and summer to  directly fuel algal
blooms when temperatures are high.

    INDICATORS OF STATUS AND FUNCTION

Physical losses of wetlands  remain the largest  problem in
maintaining the overall buffering capacity of these systems
and providing habitat  for consumers. Unfortunately, there
has been only one comprehensive effort in  the Chesapeake
watershed thus  far  to evaluate  the changes in the  entire
system (Tiner 1985). [This was done via aerial photography
with minimal sporadic field checking, so  that the non-tidal
wetlands, especially  at  the upland edges,  were  significantly
underestimated.] More accurate mapping needs to be carried
out for  regulatory and planning purposes in  the future.
There has been more intense scrutiny of tidal marshes  where
the percentage loss has been greatest. These-surveys indicate
large changes in acreage due to apparent sea-level rise  in the
mid-Bay region where  marshes are concentrated. However,
more regional approaches  are  needed which should  be
coupled to emerging geographical information systems (GIS)
to monitor  change.

Unfortunately, investigations of marsh  function in  the
Chesapeake  have been limited to comparatively few sites,
and although sediment  and  nutrient  trapping functions
have been evaluated, results have  been somewhat contradic-
tory. It is now recognized that many of these areas were
differentially affected by apparent sea-level  rise because of
differences in subsidence and external  sediment supplies.
Some of them are largely erosional (Stevenson et al.  1985) ^
while others are depositional  (Jordan et al.  1983). Modern
automated microprocessor-controlled sampling now makes
integrated  sampling more  efficient and  additional  site
analysis  possible.  Simultaneously, measurements  using
dating techniques (pollen, diatoms, and radionucleides) at
these sites to determine sediment accretion are  necessary to
assess how well these systems are functioning  over longer
time periods (decades to centuries) in regard to sea-level and
subsidence.

We know less  about the  functions of non-tidal wetlands
which makes it especially perplexing  to  evaluate  various
mitigation  schemes for alterations and  marsh  creation
(Kusler and Kentula 1991). The role of non-tidal wetlands
             84

-------
in attenuating groundwater inputs is little understood and
this function could be important to consider in mitigation
strategies.

  QUANTITATIVE AND QUALITATIVE TARGETS

Essentially,  the  quantitative targets  for  the Chesapeake
region are the same as for the nation - "NO NET LOSS."
Although this may be potentially achievable for  non-tidal
wetlands, it remains to be seen how well this goal might be
translated into the coastal marshes which  are undergoing
varying  degrees  of apparent sea-level rise. In qualitative
terms we also need to maintain  balanced  healthy systems
with a diversity of species. Therefore, we need to establish
targeted  responses to biological problems  such  as the
invasions of Phragmiles,  which  can  lower diversity,  and
nutria,  which can cause severe  eat-outs  and  subsequent
ponding of marshes. Although  not  severe at  present,
excessive beaver activity in the non-tidal wetlands can act to
reduce tree diversity by causing excessive flooding of diverse
forested  areas,

               RECOMMENDATIONS

Monitoring
Although there are up-to-date manuals for  coastal marshes
(Silberhorn 1982) and non-tidal wetland plants (Tiner 1988),
and detailed mapping of the  tidal marshes (McCormick and
Somes 1982), wetlands have  not had the same attention as
other resources  in terms of periodic "stock assessment."
Although not as difficult  a task as estimating finfish or SAV
stocks, comparatively little effort  has been put into a trend
analysis of specific wetlands, with the possible exception of
local  studies such as Blackwater  Marsh (Stevenson  et al.
1985) and the Lower  Nanticoke  (Kearney et  al.  1988) and
Chesapeake  Bay  marsh  islands  (Kearney  and  Stevenson
1991). More effort should be made to accurately map non-
tidal wetlands and to evaluate changes in coastal wetlands
due  to  sea-level  rise and   other factors  (Kearney  and
Stevenson  in  press).  Emerging technologies  of  remote
sensing and GIS may  be  helpful in assessing acreage  in the
future; but species composition  changes need to  be  moni-
tored in regard to exotics (Pbragmites and nutria),  subsi-
dence, management (e.g. marsh burning and timbering), and
hydrologic changes, and in this respect ground truthing can
not be ignored.

Research
Despite  our general understanding of coastal marsh sedi-
ments in relation to carbon  content and  bulk density
(Gosslink et al.  1984), we know surprisingly little  about
processes such  as peat  deposition  and   preservation in
various marsh systems. An  example of where this may be
critical at present is at Blackwater National Wildlife Refuge
where an arm of the embayment that was once freshwater
is extending toward the Little Choptank where much higher
salinities exist.  It is well  known that  sulfate reduction can
promote oxidation of carbon and, if liberated  from the
sediments,  catastrophic losses may occur in this region  -
forming an island in southern Dorchester County. Sulfate
is a component of agricultural runoff (Sharpley et al.  1991).
If significant  quantities  of  saline water flow  into the
Blackwater   system,  resulting in  further enrichment of
sulfate, it may cause even more peat degradation than in the
past.

Another area that requires more research is in the functions
of freshwater wetlands - both non-tidal and tidal (Silberhorn
1982). Although Odum et al.  (1984) reviewed many  of the
functional  aspects of tidal fresh marshes;  and Cahoon and
Stevenson  (1985) and Weiner and Whigham (1988) have
studied  aspects  of their population dynamics; their function
relative  to  size, configuration and location  in the  larger
landscape  is still  open  to   question. Another question
involves non-tidal wetlands: how best to mitigate losses in
terms of restoring their functional values (Kusler & Kentula
1991)? Although some work has been initiated by the Mary-
land Department of Natural Resources and  the Maryland
Highway Administration, more needs  to be done to elabo-
rate  nutrient exchange  capacities,  sediment  trapping and
other functions at different wetland mitigation sites. Special
attention needs to be paid to the  long term responses of
mitigated sites  and other constructed wetlands where sedi-
ment and  nutrient attenuation is  an issue  (Athanas and
Stevenson  1991).

Modeling
One aspect of  marsh and wetland  research in  Chesapeake
Bay  which is  obviously lacking  is  modeling to predict
responses to natural and human change. While carbon flows
have been  extensively modeled within the Chesapeake Bay
(Baird and Ulanowicz 1989)  and others  have worked on
carbon flow in  marshes (Day et al. 1973, Wiegert et al. 1975,
Randerson  1986), the connections between wetlands and the
Bay  have been largely ignored. This  is unfortunate, espe-
cially since expertise is available  at both the  University of
Maryland and  the Virginia Institute  of Marine Science. A
carbon  and/or nutrient  model would be beneficial to re-
searchers and managers, enabling  them to  target key overall
processes where more data are necessary, as well as focus on
the "big picture" which  is often  neglected in reductionist
studies.

In Louisiana, Costanza  et al. (1986) have constructed  a
spatial  model  which depicts past marsh losses due to
regional subsidence,  salinity intrusion,  canal  and  levee
construction and sea-level rise, and also can  project where
they will most probably occur in  the future.  The  model
                                                                                                                   85

-------
consists of 3,000 interconnected cells representing 1 km2 of
marsh  surface (Costanza et al. 1986).  Most management
decisions require both temporal and spatial responses  to
varying management decisions. It would be advantageous to
adapt Costanza's "GELS" model, or its  successor - "GEM,"
to  the  mid-eastern shore  (Lower  Dorchester,  Western
Somerset, Western Wicomico counties) where marshes are
likely to be lost in the near future.

Eventually  this  effort  should be  expanded  into a  more
comprehensive functional landscape model of major flows
of materials and energy between the uplands and the Bay
ecosystem. Although the concept of landscape planning is
now well established (Marsh 1983), it  has not been used
effectively in the Chesapeake region due in part to inade-
quate understanding of all  the complex  interactions  of
upland, wetland and open Bay systems. Unfortunately, the
watershed modeling that has been developed by the EPA
Chesapeake  Bay program   to  date largely neglects  the
wetland interface (Blalock and Smollen 1990).

Management
Demonstration projects need to be developed to determine
the effectiveness of management measures to reverse or slow
interior marsh loss on the extensive marshes of the Eastern
Shore. If they are designed with a research component, they
will be able to answer some of the longer term functional
questions  raised above. Also,  the use  of hydrological
modifications such as weirs and increasing bed roughness
(e.g. Christmas trees, straw bales, snow fencing)  needs to be
explored to promote sedimentation in  sediment starved
marshes to enhance retention capacities in  shallow ponds.

Another continuing management problem in the marshes
is the  issue involving Phragmites control. A workshop  on
invasive species  should be  convened to  pool information
and experiences  involving this  issue.  Another workshop
might be convened to evaluate mosquito control programs
which significantly change hydrology by cutting channels
and constructing ponds in marshes. Although initial studies
(Whigham et al. 1982) on  the eastern shore of the Chesa-
peake indicated no  significant changes in water quality due
to mosquito controls, there were changes  in species compo-
sition. The long term  impacts of these manipulations  on
marsh survival in  relation to sea-level rise  are yet  to be
determined. Finally, more effort needs to be put into nutria
control measures, possibly by encouraging trapping via a
bounty system.

Habitat Restoration
Zedler and Weller (1991) have emphasized the need for long
term evaluation of wetland restoration and creation projects.
Support  needs to be  given  to  ongoing efforts to create
and/or  replant  marshes for habitat  restoration and/or
shoreline stabilization by a) funding efforts to monitor and
evaluate the success of past and ongoing replanting efforts,
b) determining the need  to  plant or  stabilize in specific
areas  for  habitat in the Bay's watershed  and  along tidal
shorelines with the specific goal  of prioritization of sites,
and c) evaluating techniques of packaging and selling the
ideas  to landowners.

                    REFERENCES

Athanas, L.C. and J.C.  Stevenson. 1991. The use of artificial
wetlands in treating stormwater runoff.  Final Report to
Maryland Department of Environment, Baltimore, MD.

Blalock, L.L. and M. Smollen. 1990. Estimation of nonpoint
source loading factors  in the Chesapeake Bay model. Final
Report, Grant #87-EXCA-3-0829, National Water Quality
Evaluation  Project,  North  Carolina  State University &
United  States Department of Agriculture. 13 pages plus
appendices.  Printed  by the United  States Environmental
Protection  Agency  for the  Chesapeake Bay  Program,
Annapolis, MD.

Baird, D. and R. Ulanowicz. 1989. The seasonal  dynamics
of the Chesapeake Bay ecosystem. Ecological Monograph
59: 329-364.

Bartlett, K.B., D.S. Bartlett, R.C. Harriss and D.L.  Sebacher.
1987. Methane emissions along a salinity  gradient. Biogeo-
chemistry 4: 183-202.

Boyd, C.E.  1969.  Vascular  aquatic  plants  for mineral
nutrient removal from polluted waters. Economic Botany
23: 95-103.

Cahoon,  D.R.  and  J.C.  Stevenson.   1986.  Production,
predation and decomposition in a low salinity shrub marsh.
Ecology 67: 1341-1350.

Costanza, R.,  F.H. Sklar  and J.W. Day.  1986. Modelling
spatial  and temporal  succession  in  the   Atchaflaya/
Terrebonne  marsh/estuarine  complex  in  south Louisiana.
pp.  387-404.  In:  D.  Wolfe  (ed.)  Estuarine  Variability.
Academic, New York.

Day, J.W., W.G. Smith, P.R. Wagner and W.C. Stowe. 1973.
Community structure  and  carbon budget  of a salt marsh
and shallow bay estuarine system in Louisiana. Pub.  LSU-
SG-72-04.  Lousiana State  University Center for  Wetland
Resources, Louisiana State University, Baton Rouge, LA. 80
P-

Erwin, K.L. 1989. Freshwater marsh creation and restoration
in the Southeast, pp. 239-271. In: Kusler, J, and M. Kentula
 86

-------
(ed.) Wetland Creation and Restoration: The Status of the
Science.  Volume  I.  U.S.  EPA/600/3-89/038,  Corvalis,
Oregon.

Gehrels, J. and G. Mulamoutti. 1989. The transformation of
phosphorus from wetlands. Hydrological Processes 3:  365-
370.

Goodroad, L.L.  and  D.R. Keeney.  1984.  Nitrous oxide
emission from forest, marsh and prairie ecosystems. Journal
of Environmental Quality 13: 448-452.

Gosselink, J.G., E.P. Odum and R.M. Pope. 1974. The value
of the tidal marsh.  Center for Wetland Resources Publica-
tion. GSU-S-74-03, Louisiana State University, Baton Rouge,
LA, 30 pp.

Gosslink, J.G.,  R.  Hatton  and  C.S. Hopkinson. 1984.
Relationship of organic carbon and mineral content to bulk
density in Louisiana marsh soils. Soil Science 137: 177-180.

Harriss, R.C, D.L Sebacher and P.P. Day, Jr. 1982. Methane
flux in the Great Dismal Swamp.  Nature 297: 673-674.

Heinle, D.R. and  D.A. Flemer.  1976. Flows of materials
between  poorly  flooded  tidal  marshes and the  estuary.
Marine Biology  35: 359-373.

Jordan,  T.E.,  D.L  Correll  and  D.F. Whigham. 1983.
Nutrient  flux in  the Rhode  River:  Tidal  exchange of
nutrients by brackish marshes. Estuarine, Coastal and Shelf
Science 17: 651-667.

Jordan, T.E. and  D.L. Correll. 1985. Nutrient chemistry and
hydrology of interstitial water in brackish  tidal marshes of
Chesapeake Bay. Estuarine, Coastal & Shelf Science 21: 45-
55.

Kearney, M.S. and LG.  Ward.  1986. Accretion rates in
brackish marshes of a Chesapeake Bay estuarine tributary.
Geo-Marine Letters  6: 41-49.

Kearney, M.S., R.E. Grace and J.C. Stevenson. 1988. Marsh
loss in the Nanticoke Estuary, Chesapeake Bay. Geographic-
al Review 78: 205-220.

Kearney, M.S. and  J.C. Stevenson.  1991.  Island land  loss
and marsh vertical accretion rate: Evidence for historical
sea-level changes in Chesapeake Bay. Journal of Coastal Re-
search 7: 403-415.

Kearney, M.S. and J.C. Stevenson.  (In Press). Chesapeake sea
level  rise: Its  future impact on  marshes, shorelines,  and
people.  Chapter In:  David R.  Stoddart (ed.) "Human
Responses to Sea Level Rise," Proceedings of a Symposium
at AAAS 1991 Annual Meeting. Washington D.C.

Kusler, J.A. and M.E.  Kentula. 1989. Wetland Creation and
Restoration: The Status Of The Science. Volumes I &  II.
U.S. EPA/600/3-89/038, Corvallis, OR. 97333.

Le  Baugh, J.  1986. Wetland ecosystem studied  from  a
hydrologic perspective. Water Resources Bulletin 22:  1-10.

Marsh, W.M.  1983. Landscape Planning. Addison-Wesley
Publishing Co., Reading, MA, 356 pp.

McCormick, J. and Somes. 1982. The Coastal Wetlands of
Maryland,  Maryland  Department of  Natural Resources,
Annapolis, MD, 243 pp.

Mitsch, W.J. and J.G.  Gosselink. 1986. Wetlands. Reinhold,
NY, 539 pp.

Odum,  E.P.  1961.  The role of tidal marshes. New York
Conservationist: June / July, 12 pp.

Odum, W.E.,  T.J.  Smith, J.K. Hoover  and C.C.  Mclvor.
1984. The Ecology  of the Tidal Freshwater Marshes of the
U.S. East  Coast: A  Community  Profile.  U.S. Fish and
Wildlife Service. FWS/OBS-83/17. 177 pp.

Peterjohn  W.T. and D.L Correll.  1984. Nutrient dynamics
in an agricultural  watershed: observations  on  the role of
riparian forest. Ecology 65: 1466-1475.

Randerson, P.P. 1986.  A  model of carbon flow in  the
Spartina anglica marshes of the Severn Estuary,  U.K.  pp.
427-446. In: D. Wolfe (ed.) Estuarine Variability. Academic
N.Y.

Richardson, C.J. 1985. Mechanisms controlling phosphorus
retention capacity in freshwater wetlands. Science 228: 1424-
1427.

Seitzinger, S.P.  1988. Denitrification  in  freshwater and
coastal marine ecosystems. Limnology and  Oceanography
33: 702-724.

Sharpley, S.J. et al. 1991. Transport and prediction of sulfate
in agricultural runoff. Journal of Environmental Quality 20:
415-419.

Silberhorn, G.M. 1982. Common Plants of the Mid-Atlantic
Coast - A Field Guide. Johns  Hopkins University  Press,
Baltimore MD, 256 pp.

Simpson, R.L., R.E.  Good, R. Walker and B.R. Frasco. 1983.
The role of Delaware River freshwater tidal wetlands in the
                                                                                                                  87

-------
retention of nutrients and heavy metals. Journal of Environ-
mental Quality 12: 41-48.

Stevenson, J.C., D.R. Heinle, D.A. Flemer, R.J. Small, R.A.
Rowland and J.F. Ustach. 1977. Nutrient exchanges between
brackish water marshes and the estuary, pp. 219-240, In: M.
Wiley (ed.) Estuarine Processes Volume II, Academic Press.

Stevenson,  J.C., M.S.  Kearney  and E.  Pendleton.  1985.
Sedimentation and  erosion  in a Chesapeake Bay brackish
marsh system. Marine Geology 67: 213-235.

Stevenson, J.C,  L.G. Ward and  M.S.  Kearney.  1988. Sedi-
ment transport and trapping in marsh systems: implications
of tidal  flux studies. Marine Geology 80: 37-59.

Tiner, R.W. Jr.  1985. Wetlands  of the Chesapeake  Water-
shed: An overview, pp. 16-24. In: Groman et al.  (eds.). Wet-
lands of  the Chesapeake.  Environmental  Law  Institute.
Washington, D.C.

Tiner, R.W. Jr. 1987. Mid-Atlantic Wetlands: A Disappear-
ing National Treasure. Cooperative Publication, U.S. EPA
and  U.S. Fish & Wildlife Service. Newton Corner, MA, 28
pp.

Tiner, R.W.  Jr.  1988.  Field  Guide to  Nontidal Wetland
Identification, Maryland Dept. of Natural Resources & U.S.
Fish and Wildlife Service. Annapolis, MD, 283  pp.
Weiner, J. and D.F. Whigham. 1988. Size variability and self
thinning in wild rice (Zizania aquatica). American Journal
of Botany 75: 445-448.
Whigham, D.F., J. O'Neil and M. McWethy, 1982. Ecologi-
cal implications  of  manipulating  coastal  wetlands for
purposes of mosquito control, pp. 459-476. In: Gopal et al.
(eds.) Wetlands:  Ecology and Management. International
Scientific  Publications, Jaipur, India.
Wiegert, R.G., R. Christian, J.L. Gallagher, J.R. Hall, D.H.
Jones and R.L. Wetzel. 1975. A preliminary model of coastal
Georgia marsh, pp. 583-601. In: L.E. Cronin (ed.) Estuarine
Research Vol.  1. Academic Press, N.Y.
Wolaver, T.G., J. Zieman,  R.  Wetzel and K. Webb. 1983.
Tidal  exchange  of nitrogen  and  phosphorus  between
mesohaline vegetated marsh and the surrounding estuary in
the  lower  Chesapeake  Bay.  Estuarine, Coastal  & Shelf
Science 16: 321-332.
Zedler, J.B. and M.W. Weller.  1989.  Overview and  future
directions, pp. 465-473. In: Kusler, J.  and M. Kentula (ed.)
Wetland Creation  and  Restoration:  The  Status  of the
Science.  Volume  I.  U.S.  EPA/600/3-89/038,  Corvallis,
Oregon.
88

-------
FOi                  OF THIS         CONTACT
                  BAY
        410        AVENUE,       I OS
                   MARYLAND

               800-YOUR-BAY
                   O
         PRINTED ON RECYCLED  PAPER

-------

-------