Chapter 1
Program Overview and Contents
FUNCTIONAL ECOLOGY OF SUBMERGED AQUATIC
VEGETATION IN THE LOWER CHESAPEAKE BAY
R. L. Wetzel, P. A. Penhale, K. L. Webb,
R. J. Orth, J. V. Merriner and G. W. Boehlert
Editors
Virginia Institute of Marine Science
College of William and Mary
Gloucester Point, Virginia
23062
Draft Final Report
to
Mr. William A. Cook, Project Officer
Chesapeake Bay Program
U.S. Environmental Protection Agency
2083 West Street
Annapolis, Maryland 21401
April, 1981
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600R811O4
Chapter 1
Program Overview and Contents
FUNCTIONAL ECOLOGY OF SUBMERGED AQUATIC
VEGETATION IN THE LOWER CHESAPEAKE BAY
R. L. Wetzel, P. A. Penhale, K. L. Webb,
R. J. Orth, J. V. Merriner and G. W. Boehlert
Editors
Virginia Institute of Marine Science
College of William and Mary
Gloucester Point, Virginia
23062
Draft Final Report - —
to
Mr. William A. Cook, Project Officer
Chesapeake Bay Program
U.S. Environmental Protection Agency
2083 West Street
Annapolis, Maryland 21401
April, 1981
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Chapter 1
Table of Contents
I. Program Overview . 1-6
II. Chapter Contents
A. Chapter 2; Primary Production, Community Metabolism
and Nutrient Cycling ............ 7
B. Chapter 3; Interaction of Resident Consumers 7
C. Chapter 4; Higher Level Consumer Interactions t. 7
D. Chapter 5; Ecosystem Modeling i. 8
E. Chapter 6; Conclusions, Summary and
Recommendations ^....... i ;... 8
L
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PROGRAM OVERVIEW
FUNCTIONAL ECOLOGY OF SUBMERGED AQUATIC
VEGETATION IN THE LOWER CHESAPEAKE BAY
In July 1978, an interdisciplinary research team began an integrated
study of the ecology of submerged aquatic vegetation communities in the
lower Chesapeake Bay. The overall goals of the program were twofold:
1. to describe, both qualitatively and quantitatively, the principal components
of these communities and 2. to investigate what were a priori considered
the major environmental and biological interactions governing community
structure and production of both ecologically and economically important
species populations. These data were then used to determine the structure
of and input to a computer simulation model of energy flow and transforma-
tions within the seagrass ecosystem.
As of 1978, few data existed on lower Bay seagrass communities and
consequently, much of the initial efforts were devoted to descriptive studies.
Many of these studies were completed by mid-1979. The research has evolved
over the course of the program toward more experimental approaches involving
both field and laboratory investigations designed principally to elucidate
cause-effect relationships. Many of these studies have been recently com-
pleted and several are continuing. The reports that follow present the
results of all investigations completed to date (December, 1980).
At the initiation of the program, the research team adopted an approach
of both routine sampling and intensive studies in a single, unperturbed
seagrass community in the lower Bay. We decided that concentration of the
research effort in a single system would facilitate both coordination of the
program and perhaps more importantly, create as complementary and comparative
a data set, in both time and space, as possible.
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The efforts over the past 30 months can be broadly subdivided by
discipline and overall encompass investigations of:
1. Productivity, Nutrient Cycling and Community Metabolism
(Wetzel, Webb and Penhale),
2. Interactions Involving Resident Consumers (Boesch and Orth),
3. Studies of Higher Level Consumers (Merriner), and,
4. Ecosystem Modeling (Wetzel).
Studies within these areas included both field and laboratory programs. Names
in parantheses identify the responsible principal investigators.
The principal study site used during the research program is located
at Vaucluse Shores in the lower Chesapeake Bay on the Eastern Shore of
Virginia. The seagrass community in this area was chosen, because: 1.
historically, the grass bed has been persistent and stable over many years,
2. the area is generally unperturbed by man-related activities, 3. the
bed is large enough to simultaneously accomodate our various studies, and 4.
the locale is remote, allowing long term studies to be planned and carried out.
The only outside influences to the area are recreational fishing and commercial
crabbing.
The seagrass bed at Vaucluse is roughly triangular in shape, covering
a bottom area of approximately 140 hectares and is north-south oriented.
Water depths in the vegetated zones range from mean low water (MLW) to
greater than a meter deep adjacent to the western, sandbar boundary. Salinity
is nominally 18-20 °/oo and temperatures range from near 0°C in late January-
early February to 31+°C in July-August. The area shoals from south to north
and some evidence suggests the shoal sandbar is slowly migrating south.
Vegetationally, the grass bed is co-dominated by Ruppia maritima L.
(Widgeon grass) and Zostera marina L. (Eelgrass). Areal coverage is approximately
divided equally between the two species. The transects illustrated in Fig. 1
(See Chapter 1; Section 1).
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were established in July 1978 for mapping plant distribution and relative
abundance and have been used throughout the program as sampling site
references for the various studies (e.g. Orth et.al., 1979). The distribution
of the seagrasses at Vaucluse is typical of lower Bay seagrass communiites
with Ruppia dominating the shallow, inshore regions and Zostera dominating the
deeper, offshore areas. Five habitats were chosen for comparative studies;
these include Ruppia, mixed Ruppia-Zostera vegetation, Zostera. bare sub-
strate within the bed, and sand bar areas. The majority of studies within
the program have been field-oriented and directed toward interhabitat com-
parisons.
Studies completed on the submerged aquatic plant communities have
included;
1. Routine studies of plant distribution, relative abundance, biomass,
CHN ratios, rooting-depth, canopy structure (leaf area index)
analyses and substrate chemical properties.
2. Laboratory studies of ^C-photosynthesis in relation to light and
temperature.
3. Dome enclosure studies of community metabolism, nutrient exchange,
and community response to light reduction.
These studies were scheduled and carried out to include seasonal effects.
- The results of these efforts have provided extensive data sets for
correlative analyses of environmental parameters with plant growth, species
distribution and metabolic activity. These data also allow for analysis of
natural variability, and evaluation of plant community response to low-level,
short term nutrient (primary nitrogen species) enrichment and the effects
of in situ light reduction. Based on analyses of these data and the results
of more recent experiments, lower Bay seagrasses appear highly poised by
the environmental conditions of light and nutrient regimes. We have recently
begun more detailed studies of light-plant community response and environmental
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parameters governing the light-energy field in submerged aquatic communities.
These data together with new studies on the analysis of long term (4 or
more years) data sets should provide information which should allow us to
separate long term trends in environmental conditions from natural variability.
Studies of the macroinvertebrate populations inhabiting various areas
of the seagrass community and utilization of the area by waterfowl have
included a variety of activities:
1. Studies of resident, benthic macroinvertebrates have involved
routine sampling in the various habitats to describe community
structure, seasonal behavior, and to identify principal components
in terms of secondary production and trophic importance.
2. Secondary production estimates were derived for key components
through intensive sampling in specific habitats to assess energy
available to support production at higher levels.
3. Predator-prey interactions have been investigated in both laboratory
and field enclosure studies to determine the role of the seagrasses
as a refuge and the role of predation in structuring and potentially
controlling infauna and epifauna in both bare substrate and vegetated
areas.
4. Waterfowl studies were completed over two winter periods to determine
waterfowl utilization of various areas within the grassbed.
5. Tissue samples of the major species have been analyzed for various
chemical parameters including l^C/ C ratios to elucidate trophic
relations and calorimetry and C: N ratios to provide specific
conversion factors.
Structural and functional aspects of the ecology of the fish populations
utilizing seagrasses have also been investigated by combined field sampling
and laboratory studies and have generally followed the same design as that
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in studies of the benthic macroinvertebrates. The overall goals have been
to assess the importance of seagrasses to production and maintenance of
both ecologically and economically important fish populations. Studies have
been divided into three components of the populations: 1. fish eggs, larvae,
postlarvae and juveniles, 2. resident fishes and 3. migratory predators.
Initial efforts were also placed in gear comparison studies as adequate
sampling methodologies in these shallow water areas for this highly motile
group are extremely difficult. !
Specific topics addressed in the studies of this component included;
1. Recruitment and emigration studies.
2. Trophic interactions and refuge value of seagrasses.
3. Secondary production by finfishes.
4. Bioenergetic studies.
The last topic addressed in our research program was the development of an
ecosystem simulation model that would incorporate the principal biological
components of the seagrass system and simulate energy flow based on trophic
structure. Over the last 18 months the conceptual model has evolved through
three versions. The effort in this area has primarily been devoted to
establishing a realistic structure for simulation, formulation and evaluation
of mathematical interaction equation, establishing remote hardware and
software, and, establishing input data bases. Considered in this report
are the first simulation analyses with the current input data sets. These
activities represent what we consider the first stage of development and
model analysis. Continuing model studies will incorporate the results of
ongoing studies, explicit representation in the model for the forcing functions
of light and temperature, and information flows relative to nutrient conditions.
These various investigations in the research program are presented as a
coherent effort that provides basic information relative to the functional
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ecology seagrass systems in the lower Bay and makes available information
relative to the development of both general and specific criteria for
management of these important habitats. It is perhaps worth noting that we
view the completion of the present program as a first step toward the
eventual goals of management. The conclusions of the present studies as
well as the data bases themselves will require study and review as new
information is made available.
Richard L. Wetzel, Ph.D.
Program Manager
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CHAPTER CONTENTS
I. Chapter 2; Primary Production, Community Metabolism
and Nutrient Cycling
R. L. Wetzel, P. A. Penhale, M. S. Kowalski, K. L. Webb,
L. Murray and R. vanTine
A. Plant Community Structure and Sediment Properties
B. Community Productivity and Metabolism
C. Preliminary Studies of Environmental Regulation of
SAV Productivity and Community Dynamics :
D. Nutrient Cycling
II. Chapter 3; Interactions of Resident Consumers
R. J. Orth, J. vanMontfrans, R. J. Diaz and E. W. Wilkins
A. Structural and analysis of benthic communities associated
with vegetated and unvegetated habitats
B. Predator exclusion experiments in a Chesapeake Bay grass
community
C. Predator-prey interactions in an eelgrass ecosystem with
lower Chesapeake Bay, Virginia
D. Secondary production of some dominant macroinvertebrates
inhabiting an eelgrass bed of the lower Chesapeake Bay
E. Preliminary effects of grazing by Diastbma (=Bittium)
varium on eelgrass periphyton
F. Trophic relationships in an eelgrass bed based on 6 C values
G. Aspects of waterfowl utilization in a mixed bed of submerged
vegetation of the lower Chesapeake Bay
III. Chapter 4; Higher Level Consumer Interactions.
H. A. Brooks. J. V. Merriner, C. E. Meyers, J. E. Olney, G. W.
Boehlert, J. V. Lascara, A. D. Estes and T. A. Munroe.
A. Migratory predators
B. Resident fishes
C. Ichthyoplankton
D. Predator-prey experiments
E. Routine respiration of Bairdiella chrysbura
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IV. Chapter 5; Ecosytem Modeling
R. L. Wetzel and M. S. Kpwalski
A. Conceptual and Simulation Model Versions
B. Mathematical and Computer Methods
C. Parameterization and Documentation
D. Simulation and Sensitivity Analyses
E. Conclusions
V. Chapter 6; Conclusions, Summary and Recommendations
R. L. Wetzeli P. A. Penhale, K. L. Webb, R. J. Orth,
and J. V. Merriner
A. Basic Ecological Function in the Lower Chesapeake Bay
B. Potential Ecological and Socib-Economic Impact due to Loss
C. Recommendations
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