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 0C 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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