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PUBLISHED BY
THE MARYLAND DEPARTMENT OF NATURAL RESOURCES
TIDEWATER ADMINISTRATION
CHESAPEAKE BAY RESEARCH AND MONITORING DIVISION
FOR
THE CHESAPEAKE BAY PROGRAM
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Chesapeake Bay Strategy
for the
Restoration and Protection
of
Ecologically Valuable Species
Prepared by
of
September
CBP/TRS 115/94
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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
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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
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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;
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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
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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.
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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
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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;
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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
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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.
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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
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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.
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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.
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marine sediments. I. Measurement with radiotracer tech-
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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).
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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
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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
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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
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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
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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
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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
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1
"A
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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
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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
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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
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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
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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
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1
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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-
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Department of the Environment and Maryland Department
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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
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portion of Chesapeake Bay: Interpretive Report. Report to
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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
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Phillips, D.J.H., and D.A. Segar. 1986. Use of bio-indicators
in monitoring conservative contaminants: programme
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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
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Shaughnessy, A.T., LC. Scott, J.A. Ranasinghe, A.F.
Holland, and T.A. Tornatore. 1990. Long-term benthic
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the distribution of pollutants in marine sediments. Part I.
Accumulation, trophic transfer, biodegradation and migra-
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chemistry, biology, (R.A. Baker, ed.) pp. 533-554, Ann Arbor
Science, Ann Arbor, Michigan.
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response patterns of component species. Estuaries 2: 69-86.
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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.
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McCall, eds.), pp. 3-38.
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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
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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
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"" 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
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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
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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.
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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-
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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.
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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-
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Orth, R. J. and J. van Montfrans. 1990. Utilization of
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46: 126-144.
Prager, M. P., J. R. McConaugha, C. M. Jones and P. Geer.
1990. Fecundity of blue crab, Callinectes sapidus in Chesa-
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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-
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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
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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
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bacteria and algae as food sources for crustacean zooplank-
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68
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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
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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
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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
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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
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•; 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
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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
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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
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1
1
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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(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
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