OOOR79107
                    THE FUNCTIONAL ECOLOGY OF SUBMERGED AQUATIC VEGETATION

                                IN THE LOWER CHESAPEAKE BAY
                                            by

                          R.L. Wetzel, K.L. Webb, P.A.  Penhale,
                                   R.J.-Orth , D. F. Boesch,
                              G.W.  Boehlert and J.V. Merriner

                                Co-Principal Investigators

                          Virginia Institute of Marine  Science and
                     School of Marine Science College of William and Mary
                              Gloucester Point, VA.  23062
                                     Annual Data Report

                                            for

                                 EPA/CBP  Grant No. R805974

                                            to
                                    Mr.  Thomas W. Nugent
                            U.S. Environmental Protection Agency
                                        Region III
                                    6th  & Walnut Street
                                 Philadelphia, PA.  19106
                                      Project Officer
                                                                                  H
                                      November, 1979                           -nO
                                                                     ^>;>^
CB 00292

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                                           • -Xii,
                                          :.r" -  \
                    COMMONWEALTH oj: VIRGINIA
                        Virginia institute of Marine Science
,/VUJ.iAMJ HARGIS, JR              Gloi, CC^te r Poitn .  \'] Y^'miU 2 30o2                Phone'(804) 642-2111
     DIRECTOR
                                 December 10,  1979
       Mr. Bert Brun
       U. S. Fish & Wildlife  Service
       Department of the  Interior
       Annapolis, Maryland  21401

       Dear Bert:

       Enclosed please find a bound copy of our first annual data report.  The
       original unbound copy  was sent previously to Tom Nugent but as  I under-
       stand he will no longer  serve as Project Officer.  I am forwarding you
       copies in the event receipt is delayed.

       Please feel free to contact me concerning the report.  Specific comments
       should be addressed to the subproject principal investigators as indicated
       in the summary.

                                              Respectfully,
                                              R. L. Wetzel
                                              Program Manager
       RLW/ck
       Enclosure

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THE FUNCTIONAL ECOLOGY OF SUBMERGED AQUATIC VEGETATION

             IN THE LOWER CHESAPEAKE BAY
                          by

       R.L. Wetzel, K.L. Webb, P.A. Penhale,
                R.J.-Orth , D. F. Boesch,
           G.W. Boehlert and J.V. Merriner

             Co-Principal Investigators

       Virginia Institute of Marine Science and
 School of Marine Science College of William and Mary
           Gloucester Point, VA.  23062
                  Annual Data Report

                          for

              EPA/CBP Grant No. R805974

                          to
                 Mr. Thomas W. Nugent
         U.S. Environmental Protection Agency
                      Region III
                 6th & Walnut Street
              Philadelphia, PA.  19106
                   Project Officer
                   November,  1979

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                            Executive Summary

     The research program, "The Functional Ecology of Submerged Aquatic

Vegetation in the Lower Chesapeake Bay" (EPA/GBP Grant No. R805974), is

an integrative effort composed of seven principal investigators.  The

research team has worked since July 1978 at one study site, the Vaucluse

Shores area, to develop and institute a coherent research program on

SAV ecological relationships.

     The principal studies have focused on plant productivity, metabolism

and nutrient cycling, the role of resident consumers in SAV community

dynamics, the role of migratory species and efforts to develop a realistic,

ecosystem simulation model of SAV communities.

     The preliminary results of the first years study in these research

areas are contained in the following report.  Many interpretations

remain preliminary at this time.  We welcome comments and criticisms and

in particular ideas concerning data interpretation.

     Questions concerning specific aspects of the various sections

should be addressed to the following:

       1.  Productivity, Metabolism and Nutrient Cycling; R. L. Wetzel

       2.  Resident Consumers; R. J. Orth

       3.  Migratory Consumers; J. V. Merriner

       4.  Ecosystem Modelling; R. L. Wetzel

The above principal investigators are all members of faculty and staff of
                                                                    v
the Virginia Institute of Marine Science and School of Marine Science,

College of William and Mary, Gloucester Point, Virginia  23062.
                                        R. L. Wetzel, Ph.D.
                                        Program Manager

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        Productivity, Nutrient Cycling and Associated Microbial
            Metabolic Activity in Eelgrass Communities in
                       the Lower Chesapeake Bay
                R. L. Wetzel, K. L. Webb and P. A. Penhale



                             INTRODUCTION



     The productivity of eelgrass communities in temperate zone estuaries

along the U.S. East coast is comparatively very high (Billion, 1971;

Thayer, et al., 1975; Penhale, 1977).  Primary production in submerged

aquatic vegetation communities is partitioned among several components;

Zostera marina, Ruppia  maritima,epiphytes, benthic macro- and micro-

scopic algae, and phytoplankton.  Thayer et al., (1975) reports an annual

average production for eelgrass, Zostera marina, in North Carolina of

       —2    i
350 gC.m ,yr~.  Associated macrophytes in this community produce an

                                         — 7    1
approximately equivalent amount, 300 gC.m  .yr   (Thayer et al., 1975).

Partitioning of epiphytic and eelgrass production in this community was

investigated by Penhale (1977).  Working in a recently established Zostera

community, she determined that approximately 25% of the total standing

stock (epiphytes & Zostera) was epiphytic biomass and concluded that the

attached epiphytes contributed 18% to productivity of the community.

Assuming the same relationships hold for mature communities, production
                                                                    *
(exclusive of the phytoplankton and benthic microalgae) is on the order

of 600-700 gC.m  .yr~l.  Although productivity studies per se are lacking

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                                                                         2


for the Chesapeake Bay, peak live biomass determinations,as a minimum


estimate of annual production in the lower bay,suggest  production is

similar to the North Carolina area (Marsh, 1973; Orth, 1977).

     The areal distribution of seagrass communities in mid-Atlantic

estuaries is limited and generally only a few percent of total area.

However, production on a unit area basis compares with salt marsh vascular

plant production (Keefe, 1972).  In certain estuarine areas, production

by the submerged aquatic communities accounts for a significant fraction

of total estuarine primary production (Thayer et al., 1975;) and can in

large part be explained at the local level by basin morphology (Mann, 1975).

In the lower Chesapeake, seagrass communities occupy approximately

8400 hectares in mesohaline and polyhaline regions of the Bay (Orth,

Moore and fiorden, 1979).

     Limitations on productivity in seagrass communities have been

ascribed to several environmental and nutrient related parameters.  The

influence of light, temperature and salinity have received the major

research effort (Bachman and Barilotti, 1976; Biebl and McRoy, 1971;

Penhale, 1977; and references cited therein).  It is generally accepted

that the local light regime limits the subtidal distribution of Zostera;

light, temperature and probably nutrient (nitrogen) regimes interact to

control specific rates of productivity during the annual cycle, and

geographically,temperature limits the distribution of the species.

     Nutrient dynamics and specific aspects of mineral nutrient metabolism '

have received far less attention.  For temperate zone seagrass communities


along the U.S. East Coast few data are available to suggest the major
                                                                    *,
routes for nutrient flux and for one of the major nitrogen production

pathways, N-fixation, the reported data conflict (McRoy, et al., 1973;

Patriguin and Knowles, 1972).

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                                                                          3




     There is increasing evidence suggesting primary production in marine




and estuarine systems is generally nitrogen limited (Postgate, 1971;




Ryther and Dunstan, 1971, Valiela, et al., 1973; Gallagher, 1975;




Pomeroy, 1975; Orth, 1977; and others).  If temperate sea grass communities




are limited by nitrogen, they may act as competitors with other estuarine




components for available nutrients.  With the data available, we can




neither estimate the magnitude of the various nutrient interactions nor




guess their functional significance within the seagrass community or




the esturaine system as a whole.




     Organic matter production, controls affecting the primary and annual




rates of energy fixation and the mechanisms inputing energy-matter and




nutrients to higher order trophic levels and supporting secondary production




are thus not well-known.  In this report, we present our studies focused




on the above problems to investigate 1) plant distribution and relative




abundance, 2) substrate-plant relations, 3) total community metabolism




4) SAV component studies and 5) nutrient exchange studies.






                              Study Site




     Selection of the principal study site was decided by consensus of a five




member research team associated with different aspects of seagrass



research.  An approximately 260 hectare submerged aquatic vegetation bed




located in southeastern Chesapeake Bay in an area locally known as




Vaucluse Shores was chosen.  Geographically the area is situated approximately




37° 25' N. latitude, 76° 51' W. longitude.  Criteria for site selection




were;




     1.  The site has been previously studied and some background da£a




         exists,




     2.  the bed is well established and historically stable,

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     3.  the area is relatively remote and unperturbed,




     4.  vegetationally, it contains the two dominant lower bay SAV




         species, Zostera marina and Ruppia maritima, and,




     5.  it is large enough to simultaneously accomodate varied studies




         and sampling regimes.




Also, the area was a site for intensive submerged vegetation mapping




(completed July-August, 1978).  During this exercise, permanent transects




were established and were used for selection and identification of within-




site sampling stations.  Figure 1 illustrates the seagrass bed showing




transects and the distribution of submerged vegetation.  Figure 1 also




illustrates the spatial heterogeniety and distribution of the submerged




vegetation and indicates at least five distinct habitat types:




     1.  Ruppia maritima dominated community




     2.  Zostera marina dominated community




     3.  Miked vegetation areas




     4.  Within-bed bare bottom or sand areas




     5.  Sand Bar




Sampling sites were selected for each of the areas between transects




B and C and permanently marked (bouyed)  to identify stations for routine




studies.






                                METHODS








Plant Distribution and Relative Abundance;  Plant distribution and relative




abundance was determined along transects A, B and C in July, 1979 to




determine areal coverage by species and distribution with water depth.




A line-intersect method was employed using two divers and is discussed




in detail in Orth, Moore and Gordon, 1979.  Briefly, the transects marked

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Figure 1:  Vaucluse Shores Study Site.

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R = RUPPIA
Z = ZOSTERA
S=SAND
/ = MIXED
 = TRANSECTS
CHESAPEAKE
   BAY
         (D)^.
              / R/Z   .A ;
                :
                     '?**  \
                        H -

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in Figure 1 were followed from the sandbar beginning at low tide and

progressing toward the shore.  A 100 meter line marked in 10 meter intervals

was employed along the transect line to locate point intersections for

determining species composition and estimating percent cover.  At each

10 meter intersection, a 0.5m^ frame was randomly dropped and species

composition determined and percent coverage estimated by a diver.  This

procedure was replicated twice at each sampling point.  During each

transect study, time and water depth were recorded at each station for

comparison to a continuous relative tide height record kept near-shore

and for calculation of bottom depth relative to mean low water (see Orth,

Moore and Gordon, 1979).  These data also provided direct comparisons

with the previous mapping effort (July, 1978) by Orth, Moore and Gordon,

(1979) for identifying any gross differences in distribution between

years.

Substrate-Plant Relation;  Routine samples for sediment analyses in the

five habitat types were taken in July and October 1978, April, 1979 and

monthly for the period June through October, 1979.  Analyses performed

in relation to community type were dissolved interstitial nutrients

(NH^"1", N03~, N02~ and P0^~^) , adenosine triphosphate (ATP), water content,

percent organic matter (POM), particulate organic carbon and nitrogen

(POC and PON).  Sediment samples were taken by hand to a depth of approxima-

tely 30 cm using a 5 cm (diameter) acrylic core tube.  The cores were

capped underwater and sealed with tape for transport to the laboratory.

Laboratory processing consisted of decanting the top water layer, filtered,

using glass fiber filters and analysed for dissolved nutrients.  The
                                                                    t,
cores were then extruded, split vertically and cut into 0-2, 2-5, 5-10,

10-15, 15-20 and >20 cm horizontal sections.  For each core>processing

consisted of: duplicate 1 cc plugs extracted using boiling 0.1 M sodium

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                                                                          7


bicarbonate for ATP analysis (Bancroft, Paul and Wiebe, 1974); the inter-

stitial water extracted by centrifugation and glass-fiber filtered as

above and the extracts analyzed either immediately or frozen (-20°C) until

analysis; the remaining sediment fraction was frozen for later water

content/organic matter and POC/PON analyses.

     Determination of N03~, N02~, NH^+ and PC>4~3 utilized automated

analysis techniques (EPA 1974).  Modifications to these techniques include

concentration of nitrate/nitrite reagents with a corresponding reduction

in sampling rate to reduce volumes of reagent needed for analysis, a

two reagent chemistry for phosphate determination resulting in better

reagent stability and a two reagent chemistry for ammonia (Koroleff,

1970; Solorzano, 1969; Liddicoat, Tibbits and Butler, 1975; Gronuty

and Gleye, 1975).

     POC and PON analyses will be performed using a Perkin-Elmer Model

240B Elemental Analyzer.

     Water content and organic matter content was determined on freshly

frozen sediments by drying at 60°C to constant weight for water content

and ashing @ 550°C for organic matter determination.  All weights were

determined to the nearest 0.01 mg.

     Rooting depth was determined during July 1979 in the three major

vegetation areas (i.e., Ruppia, Zostera and mixed areas) by hand coring

using a 33 cm (diameter) acrylic corer.  The cores (4 replicates per area)

were taken and sectioned into 0-2, 2-5, 5-10, and 10-15 cm horizontal

sections.  Each section was washed free of sediment through a 1.0 mm screen

and roots and rhizomes sorted by hand.  The replicate samples were dried
                                                                    «.
at 60°C to constant weight (48 hours) and percent contribution to total

weight determined for each section.

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                                                                         8




Total Community Metabolism;  Total community metabolism (net community




production) within the various habitats was determined using dome enclosures.




The domes are hemispherical and measure approximately 1 m inside diameter




by 0.5 height.  Volume of the domes is ca. 260 liters and enclose a bottom




area of 0.78 m 2.  Areas within each SAV habitat type (Zostera, Ruppia,




mixed vegetation, or bare bottom) were randomly selected between transects




B and C for study.  The domes are submerged by diver and mixed using a




modified 12 VDC bilge pump in a closed loop.  The domes were sampled




through septums at regularly spaced time intervals for dissolved nutrients,




temperature and dissolved oxygen.  The dissolved inorganic nutrients




(NH4+, N02~, N03~ and PQ^~^) were determined on filtered 50 ml samples




and analyzed as discussed previously.  Dissolved oxygen was continuously




monitored using temperature compensated polarographic (Clark-type)




electrodes and calibrated using both water saturated-air nomographs  and




the Winkler technique (Strickland and Parsons, 1972).  Experiments in




each area lasted a minimum of 24 hours to bracket a complete diel cycle.




The domes within each habitat and for each study were run in duplicate




always and for some studies, four experimental domes were deployed.




Figure 2 illustrates the general experimental design.




     In addition to the parameters measured within the domes, ambient




(outside water) samples were routinely taken for the same analyses.




Light, as photosynthetically active radiation (PAR),W$B determined at the




surface and routinely light profiles taken through the water column using




a LI-COR 185A Quantum Meter.




     At the termination of experiments conducted earlier in our program^




2 or 3 randomly placed 0.085 m^ cores were taken from within the dome




enclosed area to determine SAV biomass.  Because of the high degree of




variability in these samples, we have since harvested the  entire

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Figure 2:  Dome Enclosure Experimental Design.

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                                                                          10




dome enclosed area for biomass determination.  Although very time consuming,




we feel this is the only adequate way, at the present, to evaluate replicate




dome variablity.




SAV Component Studies;  As discussed previously, the SAV community is




composed of both autotrophic and heterotrophic components in addition to




the dominant vascular plant species.  Production and metabolism (respira-




tion) by these components can significantly augment production and meta-




bolism in the seagrass community.  Studies of their production and metabolism




have been recently initiated.  We report here some preliminary findings




relative to partitioning production and metabolism between components.




     To date, component studies have focused on 1) the effects of light




on total community metabolism and specific rates of CO 2 fixation,2)




partitioning 02 and dissolved nutrient exchange between the above-ground




plant community and the sediment substrate, 3) partitioning Q£ and dissolved




nutrient exchange between the plankton, epiphytic, benthic microalgae




and the SAV community.




     The effect of light on total community metabolism was studied




intensively during July, 1979 using the dome enclosures.  Light was




reduced by 53.3% and 85.7% in adjacent domes using netting  and 62




and nutrient exchange followed for 24 hours.  The effects of light level




on the specific rates of CC>2 fixation by intact plants has been evaluated




routinely (monthly) since July, 1979 using a 14CC>2 incubation technique




(Penhale, 1977) and light level modified by neutral density screening.




     Partitioning 02 and nutrient exchange between the above-ground SAV




community and the sediment substrate was investigated in July, 1979




using dome enclosures.  Areas in the Ruppia and Zostera dominated communities




were clipped and all above-ground plant material removed in the area of




dome placement.  Adjacent non-clipped areas were also enclosed and

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                                                                           11




02 and dissolved nutrients determined over a 24 hour period.




     Partitioning the major primary producer components has just begun.




Production by the attached epiphytic community is being investigated using




a  4C02 incubation technique (Penhale, 1977).  Plankton community meta-




bolism and primary production are being investigated using the standard




light-dark bottle technique and ^C02 incubation technique respectively




(Strickland and Parsons, 1972).  Benthic microalgae metabolism is being




studied using 1 liter in situ chamber incubations.  Oxygen determinations




from light and dark chambers are determined at routine sampling intervals




on 10 ml fixed samples and titrated using a microliter buret (resolution




=0.1 ul).  We present in this report some preliminary data to illustrate




the experimental designs.




Nutrient Exchange Studies;  Kinetic studies of dissolved inorganic nutrient




exchange employs the same experimental design as the production/metabolism




studies of plankton and SAV communities.  The incubations (glass 300 ml




bottles for plankton and domes for SAV habitats) are run at ambient levels




and spiked (nutrient enriched) to approximately lOx ambient levels.  Decay




of the spiked samples is followed over time with the sampling intervals




adjusted to the decay rate and continued sampling until ambient levels




are reached.  These studies are conducted simultaneously with the production/




metabolism experiments.  Analyses for Ntfy"*", N03~, N02~ and P04~^ are




as previously discussed.








                                RESULTS








Plant Distribution and Relative Abundance; Plant  distribution and percent




cover, as a estimate of  relative abundance, was determined along transects

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                                                                           12

A, B, and C in July, 1979.  Figure 3 illustrates the distribution by

species relative to water depth at mean low water and percent cover

along the transects.  Ruppia  predominated in the shallower depths and

Zostera predominated in the deeper areas  (adjacent to the sand bar).

In the shallower subtidal areas along transects B and C an unidentified

algae contributed significantly to percent cover.  These data support

the general conclusions reported by Orth, Moore and Gordon (1979) of the

depth dependent distribution of Ruppia -  Zostera  plant association

but also indicate that the relationship is not a simple function of water

depth alone.  Ruppia occurs in the deeper areas generally dominated

by Zostera  (Transects A, B and C) and Zostera occurs in some shallower

depths normally occupied only by Ruppia (Transect A).

Substrate - Plant Relationships;  The results of the analyses for

rooting depth of the dominant plant species in the three vegetated zones

are presented in Table 1.  The data suggest that in the Ruppia  community

a greater percentage of the below ground  root and rhizome biomass is

located in the top 5 cm and Zostera appears rooted deeper in the substrate.

However, for all vegetated areas, greater than 98% of the root-rhizome

system is located in the upper 10 cm of sediment.

     Sediment profiles of dissolved interstitial NH^+ and N03~ and

sediment ATP concentration for various times of year are presented

in Figure  4 and Figure 5, respectively,for the four habitats within the

seagrass bed.  Table 2 summarizes the percent of total ATP (to a depth

of 30 cm), contained in the top 5 and 10 cm core fractions.   The data

indicate both between habitat variability and suggest  strong seasonal
                                                                    v
changes in all areas.  The major distributional changes with depth for

both NH,  and ATP in the vegetated areas appears to occur at  or near the

maximum depth of rooting (see Table 1).

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                                                                              13
Figure 3:  SAV Distribution and Relative Abundance along Transects A, B,
           and C, Vaucluse Shores, July 1979.

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E
o
cc
UJ
o
o
              JOO
                       200
                                300      400      5OO
                                                           600
                                                                    TOO
                                                                             MO
    601

   ioo
                                                     TRANSECT  C
O
o
                                                                KEY
P Z. marine


* ft. moritima


" Algae
                                300      400
                                                  50O

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                                                                           14
TABLE 1:  ROOTING DEPTH ANALYSES
SPECIES
RUPPIA MARITIMA


MIXED BED



ZOSTERA MARINA


DEPTH
TCM)
0-2
2-5
5-10
1015
0-2
2-5
5-10
10-15
02
2-5
5-10
10-15
x + S.D,
% TOTAL WT, % 0-5 CM
67 + 9,7 89, +3,0
22 + 10,0
9 + 3,3
2 + 0,96
55 ±4,6 83 ±11,
28 + 15,2
15 + 10,1
2 + 2
51, + 14, 93, + 3,2
42, + 15,9
6, +2,6
0,7 + 0,58

%0-10 CM
98, +1,0


98 + 0,6



99 + 0,6



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                                                                              15
Figure 4:  Sediment Profiles of NH* and N0~; October  1978 and July  1979.

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 jil M  N-MH4

125   250  379  5OO
                                                  N-N03
                                                 10    15  20
Z
              J	I	I	1
                                            I	I	I	I
  20-20
                                             = OCTOBER, 1978
                                             = J ULY, 1979

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                                                                              16
Figure 5:  Sediment Profiles of ATP by habitat for various times of year.

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   IL.L   u.

                  O I

                  o O
                  " c


                  tl
                  < t-
                  09
viddna
HDiVd QNVS
VH31SOZ
«va QNVS

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                                                                           17
TABLE 2:  PERCENT TOTAL ATP IN 0-5 AND 0-10 VERITAL CORE SECTIONS



                                      78     78     .  79      79
SPECIES
RUPPIA

SAND PATCH

MIXED

ZOSTERA

SAND BAR

DEPTH (CM)
0-5
0-10
0-5
0-10
0-5
0-10
0-5
0-10
0-5
0-10
JULY
61
90
49
79
N,D,
N,D.
55
80
37
65
OCT
32
68
43
70
46
82
54
80
64
83
APRIL
65
86
55
75
48
70
56
81
35
57
JUNE
58
91
37
66
35
55
65
86
23
38

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                                                                           18



Total Community Metabolism;  Tables 3 and 4 summarize the results of the



dome 0- exchange studies.  The 24 hour rate estimates net community daily



production or consumption of oxygen and is the simple difference between



starting and ending concentrations.  The mean apparent 02 production



rates during the daylight period were determined by averaging all daytime



rates from the domes.  The mean apparent 0- consumption (community



respiration) rates were determined by averaging all nightime rates from



the domes.



     Net Community Production (NCP) as estimated by the 24 hour difference



was highly variable in both Ruppia and Zostera areas for the periods



reported.  In Ruppia, the highest negative values (6/79 and 7/79) for



community consumption over a 24 hour period occurred when low tide



coincided with the period of maximum insolation and may suggest inhibition



of photosynthesis under high light regimes.  (PAR = 1134 to 1323


    -2    -1
uE-m  -sec   at bottom).  At other times of the year, NCP was generally



positive except during the September, 1979 study.  During this period



high tide occurred during the middle of the day and light was reduced


                    -2    -1
(PAR = 30 - 300 uE-m  -sec  ) during the period of maximum potential



photosynthetic activity.  In the Zostera area, NCP was variable and for



the majority of dome studies (4 of 7) was negative.  Net negative values



for 0~ exchange in Zostera were associated with high tides during the


                                                                 —2
day coinciding with periods of maximum insolation (PAR = 350 uE'm  -sec-1,



1330 hours at the bottom in September, 1979).  However in July 1979, NCP



was highly positive with high tide occurring during the middle of the



day.  During this period water turbidity was low, no cloud cover and

                                                                    t

maximum insolation for the dates were reported (.100% maximum sunshine,



Norfolk Weather Station).  Light reaching the bottom during the study


                                  -2    -1
period ranged from 500 to 760 uE'm  -sec

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                                                                 19
(MO/DY/YR)
10/11/78
10/12/78
4/27/79
4/28/79
5/2/79
5/2/79
6/23/79
6/23/79
7/17/79
7/18/79
7/20/79
8/27/79
8/27/79
9/25/79
9/25/79
10/24/79
10/24/79
TIDE
(TIME)


0947 HT
1030 HT
1343 HT
1435 HT
1416 LT
1416 LT
0926 LT
1027 LT
1126 LT
1156 HT

1122 HT

1056 HT

L.
, 2S HR-?N
(MG02-M O
+863,
- 99,6*
«_
+127,
- 78,5
+181,*
— ...
-1760,
-1089 ,
790,*
+332,
+498,
+996,*
-108,
+266,*
+266,
+448,*
, X DAY9 v
(MG02'MZ'HR -1)
339,
392,*
•mm —
86,4
108,
165,*
398,
418,
286,
365,*
129,
+335,
+339 , *
+116,
+359,*
304,
335,*
X NIGHT i
' (MG02'M-2.HR -1)
-325,
-246,*
- 84,8
-144,
-122,
-154,*
«_
-491,
-309,
-236,*
-282,
-136,
-123,*
- 66,
-116,*
- 37,2
- 25,2*
= NUTRIENT SPIKE EXPERIMENT

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                                                                   20
DATE TIDE
(TIME) (
10/16/78
10/17/78
4/30/79 1202 HT
6/25/79 0947 HT
6/26/79 1029 HT
7/26/79 1040 HT
7/27/79- 1117 HT
7/27/79
8/29/79 1321 HT
9/27/79 1250 HT
10/29/79 1535 HT
t.
24 HRo
^MGuo'M /
+239,
-322,
-883,
- 39,8*
+551,*
+770,*
-2025,
-1643,*
-926,
-1368,*
+598,*
+531,*
, X DAY_o n
(MG02-M ^'HR -1)
196,
193,*
276,
212,
335,*
+333,
+307,*
+385,
116,
178,*
252,
219,*
316,
261,*
X NIGHIo i
I Wl^**f \f\ • M • LJ D ^^ 1
-86,3
-226,*
-177,
-99,6
-26,6*
-86,2
-133,
-133,
-199,
-206,*
-166,
-173,*
-81,*
* _
  = NUTRIENT SPIKE EXPERIMENT

-------
                                                                           21



     Mean hourly 0- production rates during the day and mean hourly



0- consumption during the night were less variable both among and between



vegetated communities.  0- production in both communities peaked in early



summer followed by a late summer depression and again increased in early



fall.  0- consumption in the Zostera community remained relatively constant



during the period April to October, 1979 with values ranging from 100-200


      -2   -1
mgO^-m  -hr  .  0- consumption in the Ruppia community varied over the


                   -2   -1                                      -2   -1
range of -50 mgO_-m   -hr   to a late June maximum of -570 mgO?-m  -hr



During this later period of maximum values (June to July) it was observed



that Ruppia was highly colonized by hydrozoans.







Nutrient Exchange Studies;  The experimental approach we have used to



produce the kinetic parameters for relationships between nutrient uptake



and rate of utilization have been in part to enrich the dome incubation



chambers to elevated concentrations and follow the concentration decay



with time.  Uptake kinetics for inorganic nutrients and other reactive



substrates are most often described by the Michaelis-Menten enzyme-



substrate analogy:  i.e., a retangular hyperbola of the rate vs substrate



concentration or by the hyperbola plus a linear diffusion component.



The relationship is described mathematically by the equation:



                       Vm. Cs3

                   V - CS3 -k
                           s


        where:  Vm = maximum rate

                fe] = substrate concentration

                k  = substrate concentration at which V = 0.5 Vm
                 s


The equation is modified by:
                   v-PCJ- \  TU


        where d = diffusion constant

-------
                                                                           22
to include diffusion.  The mathematical description is both useful for



data reduction, understanding the system and for modelling purposes.



The decay curves resemble the solid line of Fig. 6C for the hyperbola



represented in Fig. 6A.  The linear portion of the decay curve is



representative of the maximum rate.  In some experimental situations the



concentration never decays to zero but comes to equilibrum at some positive



concentration (dotted lines of Fig. 6C & 6D).  This is interpreted as



either (a) there exists a threshold concentration below which there is no



uptake or (b) there are components of the system which are producing the



material in question and this is the concentration at which the processes



balance.  If there is a diffusion component (as there often is for ammonia)



the decay curve will resemble that of Fig. 6B and there will be no linear



portion of the uptake curve, i.e., the rate cannot be saturated.  At



this point in time our data analysis has progressed only to the point of



calculating V   , i.e., the saturated rate.
          6  max'     '



      Figures 7A and B illustrate the decay (uptake) of NH, in replicate



experiments in the Ruppia community.  Uptake was extremely rapid during



the photoperiod (1200 to 1600 hours) and decayed   asympotically, to



ambient levels in less than 24 hours.  The data suggest at least a two



component system perhaps related to photoperiod.  Figures 7C and D


                                   -3       -
illustrate the decay (uptake) of PO,  and N0_ during the same period



in the Zostera area.  N0~ uptake followed a pattern similar to NH,



in the Ruppia area but appears slower from inspection of the slopes of



the decay curves.  Figures 8A and B illustrates the uptake of NflT and



NO, in a mixed spiking experiment (i.e. both NH, and NO, added to the



domes in combination).  The initial decay rates indicate NH, is taken up



faster than N0_, and suggest  a preference for NH,.  Figure 9 illustrates



the uptake of NH, in a double spiking experiment in the Zostera community

-------
                                                                              23
Figure 6:  Mlchaelis-Menten Uptake vs Substrate Concentrate Curves with
           and without a Diffusion Component (A & B) and Typical Decay
           Curves for Substrate Utilization (C & D).

-------
                                                                                     UJ
                                
 E
>
m

-------
                                                                              24
                              T                                      -'
Figure 7:  Decay Curves for NH, Uptake in the Ruppia Community and PO ~

           and NO" Uptake in the Zostera Community  (October 1978) .

-------
8   8   8  S   §   8  °
  o
  ID
  UJ
  2
  o
  o
  o
  UJ
- Q.
  I 10
  O
  z

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  z
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                              C

                              5
         00

         co

       o  o
      Nj O
     -oooi


     - 0083


     - 0093


     -00t>3


     -0033   9j

             O
    r 0003   3

             UJ

     - 0081    2

             H

    -0091


    - OOtH


    -0031


    -0001


    -0080





     -OOOZ


     -0083


     -0093


     -00*3   _


    H0033   ^

             O
     - 0003   X

             UJ
     -0081    •£

             I-
    -O09I


     -OOfrl


     -0031


     - 0001


      0080
             9
9   o
               £-
                 Od

-------
                                                                              25
Figure 8:  Decay Curves for NH, and NOl Uptake in Ruppia Community  (July,  1979)

-------
I
z
10-
 9-
 8-
 7-
 6-
 5-
 4-
 3-
 2-
 I-
                                             SPIKE
                                 Ruppia maritime
                                     JULY 1979
o
z
            0.5
    (1100) (1130)
               i.O     1.5    2.0    25    3.0     5.5    9.5    13.5   17.5
              (1200)  (1230) (1300)  (1330) (1400) (1630)  (2030) (0145) (0545)
                                      T(hr)

-------
                                                                              26
Figure 9:  Decay Curves for Double NH, Spike in Zostera Community  (July,  1979)

-------
~
m
r
in
     ~  o
                                   in
                                            in
                                            CM
                                                     -SI9I
                                                     -0191
                                                     -S09I
                                                     -0091
                                                     -QQSI
                                                     -OSSI
                                                     -SfrQI
                                                     -SCSI
                                                     -S3SI
                                                     -OZSI
                                                     -SIS)
                                                     -01 SI
                                                     -SOS I
                                                     -OOSI
                                                     -SSfrl
                                                     -OCfrl
                                                     -SEfrl
                                        -   O

-------
                                                                           27
during the day.  The calculated uptake rates from the two spikes are not



significantly different and indicate the uptake system is saturated and



operating at Vmax.



      Table 5 summarizes the summer experiments from the Ruppia and



Zostera areas in terms of nitrogen uptake rates assuming saturated systems



kinetics.  These few data suggest that Vm is similar for NH, and NO,



and the rates appear higher in the Zostera community.  During this sampling



period, the ambient or control domes were variable in relation to NH,  and



N0_ behavior and indicated no net uptake or release of either nitrogen



species except for the August, 1979 study in Zostera.  In the ambient  dome,


                             -2   -1       +
a net release of +110 ug-at-m  -hr   and NH.-N was realized.



      These types of experiments have been done for each study period



indicated on the table's summarizing the 0~ exchange data.  However, the



data on nitrogen exchange has not been reduced to the point where kinetic



parameters can be calculated.  The above data is presented to illustrate



the potential information contained in the experimental designs and data



analysis technique employed with such information.



SAV Component Studies;  Studies were initiated during 1978 and 1979 to



partition total community metabolism and nutrient exchange into water



column processes, above-ground plant community processes, sediment



processes and to begin studies on the relations between light, nutrient



exchange and community metabolism.  These efforts are just beginning and



the experiments reported herein were designed primarily to illustrate  our



approach and as screening experiments for designing and allocating future



research effort (1980).

                                                                    V

      Photosynthesis and respiration of the plankton community was



investigated using light and dark bottle incubations (300 ml BOD bottles)



and the   CO- incubation technique using various light regimes.  Table 6

-------OCR error (C:\Conversion\JobRoot\00000ANE\tiff\2000W6CW.tif): Unspecified error

-------
                                                                29
 TABLE 6:   SUMMARY OF LIGHT-DARK BOTTLE EXPERIMENTS,

JULY, 1978
OCTOBER, 1978
X MG(
GP1
39,4
(6,0)
—
• M J LJD •*•
s ' I I • nr\
NP2
19,9
(5,2)
63,8
(±1,9)
R5
23,4
(4,4)
—
 APRIL,  1979            63,6       46,4      21,6
                       (40,8)     (39,8)     (9,0)
1,  GROSS PRODUCTION
2,  NET PRODUCTION
3,  RESPIRATION

-------
                                                              30
TABLE 7:  PHYTOPLANKTON PHOTOSYNTHESIS
DATE              PMAX
              (MG C M~* HR~1)      (u E
JULY, 1978         180,                 75,

OCT., 1978          93,                WO,

JULY, 1979         160,                 83,

-------
                                                                      31
TABLE 8A:
                  PHOTOSYNTHESIS:
                  PERCENT OF TOTAL
                  IN 15 UM & LESS
                  FRACTION,
CHLOROPHYLL A:
PERCENT OF TOTAL
IN 15 UM & LESS
FRACTION,
TIME
(H)
1000
1400
1800
2200
0600
MGC-M ,HR~-"-
67,
82,
71,
75,
83,
DRIFT STUDY
43,
103,
99,
80,
102,
BAG ENCLOSURE
43,
64,
86,
78,
78,
TABLE
                                        (±S,D,)

TIME
1000
1400
1800
2200
0600


DRIFT
T
10
2
2
4
1
, +
,81
,5
,11
,99
,66
,064
,36
,179
,192
STUDY
F
4,28 +
2,88
2,48
3,29
2,03
BAG STUDY

,128
,192
,256
,128
,256

10,
5,
4.
4,
4,
T
+
61
37
5
54

,66
,279
,144
,38
,111

4,
3,
3,
3,
3,
F
28 +
58
73
55
55

,128
,064
,064
,111
,000

-------
                                                                           32



summarizes light-dark bottle studies for various seasons as measures of



community metabolism.  Characterization of phytoplankton photosynthesis



for various seasons and  light saturated rates are summarized in Table 7.



      The light intensity photosynthesis relationship can be described by



a hyperbola where P    is the maximum rate of photosynthesis and I,  is
                   max                                            k


the light intensity at which the initial slope would intersect the P
                                                                    max


value if it were extended.  These values will be used to model phytoplankton



production as well as indicate the physiological state of the phytoplankton.



      The phytoplankton responsible for most of the primary production in



Chesapeake Bay as well as other estuaries are usually the very small forms,



i.e. less than 15 micrometers in diameter.  During July 1979, we monitored



both the total (T) chlorophyll ji and the chlorophyll a_ in the size fraction



less than 15 urn (F).   Samples were taken both from a boat drifting with



the water mass across the grass bed and from a large bag enclosure filled



at the start of the "drift study" and kept suspended at the surface of



the water column.  Photosynthesis was measured on water samples taken



from the middle of the grass bed.  Table 8A and B summarize the results



of these analyses.  Table 8A summarizes chlorophyll ji and photosynthesis



distribution by phytoplankton size class.  Table 8B summarizes chlorophyll



a^ concentrations for the total (T) and less than 15 urn size fractions(F).



Table 9 summarizes the values for P    and I,  of the light photosynthesis
                                   max      K.


relationship for the total (T) and less than 15 urn size fraction (F)



during the study.  All data in the above studies is for July 28 to 29,



1979.



      The effect of light reduction (shading) on total community metabolism

                                                                    *,

in the Zostera area was studied in July, 1979.  Shades were constructed



of seine netting to reduce ambient light in the dome enclosures by



approximately 50 and 85 percent.  Table 10 summarizes the data for 0_

-------
TABLE 9:                                                            33
RELATIONSHIP BETWEEN PMAX AND IK FOR TOTAL  (T)  AND LESS THAN
15 JJM FRACTION  (F);  vIllLY, 1979,
PMAX
(MG C M JH ±
TIME
1030
1414
1815
2400
0600
T
157,
87,8
50,2
63,6
56,9
F
105
72,1
35,6
47,4
47,3
F
(MG C
T
15,8
31,3
20,0
15,5
28,8
DMAX 11 S 1
MG CHLA H ) (U E M '-S -1)
F
24,6
25,1
14,4
14,4
23,3
T F
83,8 94,2
112, 80,5
79,5 84,2
78,5 78,5
— —

-------
                                                                 34
TABLE 10:  EFFECTS OF SHADING ON ZOSTERA COMMUNITY METABOLISM,
TIME 0
PRE-SHADE 554,
SHADED
(LATE AFTERNOON) -
SHADED
(MORNING)
POST- SHADE
53-32
498,
50,
153,
299,
85,7%
774,
7,
86,
531,

-------
                                                                           35



exchange.  The reduction in apparent 0_ production rates, as a percentage



of pre-shading rates, was 69% and 89% in the 53% and 85% treatments



respectively.  Ambient light reaching the bottom was high (200-750


    -2    -1
uE'tn  -sec  ) during the photoperiod and suggests that if the community


                                                     -2    -1
does light saturate, saturation occurs above 300 uE-m  -sec  .  Specific


                  14
experiments using   C tracer techniques have been designed to address



this relationship but the data have not been analyzed due to radioisotope



counting equipment failure.  However, experiments have been conducted



since July, 1979.  Nightly respiration values (rates) were not significantly



different between shaded and non-shaded domes and are not included in the



summary table.



      Partitioning 0~ exchange and nitrogen exchange between the above-



ground community and the substrate was investigated in August, 1979.



Areas in both Ruppia and Zostera communities were clipped (i.e. all above-



ground plant material harvested) to allow placement of the domes.  Table



HA summarized 0~ exchange in clipped and non-clipped areas.  Table 11B



summarizes the nitrogen exchange information for the Ruppia area.  For



0« exchange, mean 0  production was reducedc during the day by 50% and



the 24 hour estimate of net community production was reduced by 89% in



the Ruppia dominated community.  Under the conditions prevailing during



the Zostera study, mean 0_ production during the day was reduced by 78%



and the net negative community production rate for the 24 hour reduced



by 93%.  The maximum velocity (Vm) for uptake of both NH,- and N0~ was



reduced by 55% and 53% respectively in the Ruppia community by eliminating



the above-ground material.  Assuming that the plankton community is

                                                                    t

contributing little to the calculated rates, it would appear that in the



shallower Ruppia area, photosynthesis by autotrophs associated with the



sediments is high and in both areas, the major component influencing



respiration  is sediment related.

-------
                                                                 36

TABLE 11;  ABOVE-GROUND AND SUBSTRATE PARTITIONING EXPERIMENT:

A,  0  EXCHANGE
DATE
8-28-79
8-29-79
AREA
RUPPIA*
RUPPIA**
ZOSTERA*
ZOSTERA**
A24 HR,
+854,
+ 93,5
- 20,4
-308,0
°2 ? .
X MGQ2'M~ -HR"1
(DAY)
+195,
+ 98,
+ 67,5
+ 15,7
B,  NITROGEN EXCHANGE

                                           9    1
DATE         AREA                 UG-ATN-M  -HR
                               NHj             N03

8-28-79RUPPIA*61CK475?
             RUPPIA**          250,            224,
*= NON-CLIPPED
**=CLIPPED

-------
                                                                          37
                               DISCUSSION

     Plant distribution and relative abundance along transects A, B,

and C at the Vaucluse study site closely follows the results reported

by Orth, Moore and Gordon (1979).  This distribution relative to water

depth appears characteristic of the lower Bay mesohaline and polyhaline

environments.  The lower limit for Zostera marina is probably controlled

by available light.  However, there is some indication in the distribution

data (Figure 3) that the interaction between Ruppia and Zostera is not

simply explained by water depth.  For both species, occurrance has been

recorded at depths outside their typical ranges.  At Vaucluse, in the area

adjacent to the sand bar occupied predominately by monospecific stands of

Zostera marina, Ruppia was observed inhabiting the fringes of what appeared

to be recently established bare sand areas.  In addition to light, it

appears that the relative distribution and abundance of Ruppia-Zostera

seagrass communities is influences by other factors; current is suggested

as one possible contributing factor to the observed patterns.

     Plant-substrate relations in terms of nutrient relations are difficult

to interpret due to the limited amount of data reduced at this time.

The depth of the rooting zone in the vegetated areas appears to correlate

with the distribution of ATP and NH,; the major inflections occurring

at 5-10 cm deep.  In the summer (July), NH, pore water concentrations are

high in the deeper sediments (>10 cm) and N0_ low.  In the fall (October)

during the second growth period, NH, is generally reduced throughout the

sediment with depth and N0_ increased.  ATP concentrations, as an estimator

of heterotrophic biomass, is highest in the warmer months and corresponds
                                                                    k
to the periods of highest community respiration measurements.

-------
                                                                           38




     Nixon and Oviatt (1972) repotted apparent 0« production and respiration


                  -2    -1              -2    -1
rates of 2.9 gO^-m  -day   and 3.6 gO-'m  -day   respectively for a pond


                                                        _2
eel grass community and 0,, production values of 3.6 gO~;m  'day for a



riverine eelgrass community.  These values are for the midsummer.  Assuming



the mean rates presented in Table 4 for June, July and August represent



the mean hourly rate over the photoperiod and the respiration values are



typical of the hourly rate over the diel cycle, mean hourly rate of


                                                     -2   -1
respiration for the three month period is -143 mgO -m  -hrr .  This



compares favorably with the value reported for the pond eelgrass community.


                                                                       -2   -1
For the same period, the mean hourly production rate equals +267 mgO -m  -hr



The mean daylight period at this latitude during the period June-August



is 14.1 hours.  If the photoperiod during which this mean production rate



is realized is 80% of the daylight period, or approximately 11.5 hours,



mean daily CL producting during the period for the Zostera area would


                 -2    -1
equal +3.07 gO -m  'day  .  This compares favorably with the results of



Nixon and Oviatt (1972) and suggests the community is net negative with



respect to daily production.  Mean daylight 0« production and night



respiration values in the Ruppia community compare with the Zostera area



(Table 3).



     The data from the dome 0_ exchange studies suggest two potentially



valuable lines of research with respect to factors controlling community



metabolism, productivity and nutrient cycling.  The effect of light on



distribution and production has been alluded to previously.  It appears



from the data that available light governs the specific rate of net



community production or consumption of oxygen and that the community,

                                                                    \

at least the Zostera area, is not operating in a light-saturated environment.

-------
                                                                          39


Small changes in available light due to either weather conditions or

possibly turbidity levels have pronounced effects.  The results of one study

in the Ruppia dominated community also suggest that high light may inhibit

apparent production by this species.  The reasons for this are not clear

but do suggest that available light is singularily a primary control in

both communities.  Tables 3 and 4 also summarize, in terms of mean hourly

rates, 0_ production and respiration and the effect of nutrient (NH, and

N0_) additions to plant communities.  In the Ruppia area, the majority

of spike experiments resulted in increased apparent CL production during

the day.  The percent increase over ambient rates ranged from 1% to

210% with maximum increases occurring in early summar and fall periods.

In the Zostera community the effect was not as pronounced.  Increases

were observed in the summer months (June through August) and averaged

30% increase in apparent hourly CL production rates during the day.  At

other times of the year either no effect was observed or the rate slightly

reduced (Table 4).  Whether these increases can be attributed to the

vascular plants per se is not known but the community as a whole responded

to the increased nitrogen supply.  Based on this information more refined

experiments are planned for light, nutrient and productivity studies for

the following year.

      Partitioning the processes of production, respiration and nutrient

exchange into components of the SAV community has just began and the data are

preliminary.  It appears from the light-dark bottle studies that plankton

community production compared to the SAV communities is small; i.e. on

the order of 10% net daytime community production.  The clipping experiments
                                                                    %
(Table 11) indicate that in certain areas, benthic algal production may be

significant and the major respiratory demand of the community is associated

with the sediments.  Our future studies will evaluate these processes in

more detail with regard to energy flow and nutrient exchange.

-------
                                                                          40




      These studies and the data gathered from the various experiments




will provide the modelling effort the necessary information to realistically




simulate energy flow and the effects of light and nutrients in the plant




dominated communities.  Unfortunately for this report much of the data




has not yet been reduced and interpreted for inclusion.  The data presented




however is representative of our overall effort and indicative of our




findings to date.

-------
                                                                              41

                               Literature Cited

Blaclaiian, T. W. and D. C. Barilotti.  1976.  Irradiance Reduction:  effects
     on standing crops of the eelgrass Zostera marina in a coastal lagoon.
     Mar. Biol.  34:33-40.

Bancroft, K., E. A. Paul and W. J. Wiebe.  1976.  The extraction and
     measurement of adenosine triphosphate from marine sediments.  Limnol.
     Oceanogr.  21:473-480.

Biebl, R. and C. P. McRoy.  1971.  Plasmatic resistance and rate of
     respiration and photosynthesis of Zostera marina at different salinities
     and temperatures.  Mar. Biol. 8(l):48-56.

Billion, C. R.  1971.  A comparative study of the primary productivity of
     estuarine phytoplankton and macrobenthic plants.  Ph.D. Dissertation,
     Univ. North Carolina, Chapel Hill.

Gallagher, J. L.  1975.  Effect of an ammonium nitrate pulse on the growth
     and elemental composition of natural stands of Spartina alterniflora
     and Juncus roemerianus in a Georgia salt marsh.  Amer. J. Bot. 62:644-648.

Gravitz, N. and L. Gleye.  1975.  A photochemical side reaction that interferes
     with the phenolhypochlopite assay for ammonia.  Limnol. Oceanogr.
     20:1015-1017.

Keefe, C. W.  1972.  Marsh production:  a summary of the literature.  Contri.
     Mar. Sci.  16:163-181.

Koroleff, F.  1970.  Direct determination of ammonia in natural waters as
     indophenol blue.  pp. 19-22.  IN;  Information of Techniques and
     Methods for Seawater Analysis.  ICES, Service Hydrographique, Interlab
     Report 3.

Liddicoat, M. I., S. Tibbitts and E. I. Bulter.  1975.  The determination of
     ammonia in seawater.  Limnol. Oceanogr.  20:131-132.

Mann, K. H.  1975.  Relationship between morphometry and biological functioning
     in three coastal inlets of Nova Scota.  pp. 634-644.  IN;  Cronin, L. E.
     (ed.).  Estuarine Research, Vol. I., Academic Press, N.Y.  738 pp.

Marsh, G. A.  1973.  The Zostera epifaunal community in the York River,
     Virginia.  Chesapeake Sci., 14:87-97.

McRoy, C. P., J. J. Goering and B. Chaney.  1973.  Nitrogen fixation associated
     with sea grasses.  Limnol. Oceanogr. 18:998-1002.

Nixon, S. W. and C. A. Oviatt.  1972.  Preliminary measurements of mid-
     summer metabolism in beds of eelgrass, Zostera marina.  Ecology 53:150-153.
                                                                       \
Orth, R. J.  1977.  Effect of nutrient enrichment on growth of the eelgrass
     Zostera marina in the Chesapeake Bay, Virginia, U.S.A. Mar. Biol.
     44:187-194.

-------
                                                                              42
Orth, R. J., K. A. Moore and H. Gordon.  1979.  Distribution and Abundance
     of Submerged Aquatic Vegetation in the Lower Chesapeake Bay.  Draft
     Report to EPA; Contract No. R805951010.

Patriquin, D. and R. Knowles.  1972.  Nitrogen fixation in the rhizosphere
     of marine angiosperms.  Mar. Biol. 16:49-58.

Penhale, Polly A.  1977.  Macrophyte-epiphyte biomass and productivity in
     an eelgrass (Zostera marina L.) community.  J. exp. mar. Biol. Ecol.,
     26:211-224.

Pomeroy, L. R.  1975.  Mineral cycling in marine ecosystems,  pp. 209-223.
     IN;  F. G. Howell, J. B. Gentry and M. H. Smith (eds.).  Mineral
     Cycling in Southeastern Ecosystems, NTIS, CONF-740513, Springfield,
     Va.

Postgate, J. R.  1971.  Relevant aspects of the physiological chemistry
     of nitrogen fixation,  pp. 287-307.  IN;  D. E. Hughes and A. H. Rose
     (eds.)., Microbes and Biology Productivity.  Symp. Soc. Gen. Microbial.,
     Vol. 21, Cambridge University Press, London.
                                                                        \
Ryther, J. H. and W. M. Dunstan.  1971.  Nitrogen, phosphorous and eutro-
     phication in the coastal marine environment.  Science, 171:1008-1012.

Solorzano, L.  1969.  Determination of ammonia in natural waters by the
     phenolhypochlorite method.  Limnol. Oceanogr.  14:799-801.

Strickland, J. D. H. and T. R. Parsons.  1972.  A practical Handbook of
     Seawater Analysis.  2nd ed. Bull. Fish. Res. Bd.  Canada 167.

Thayer, G. W., S. M. Adams, and M. W. LaCroix.  1975.  Structural and
     functional aspects of a recently established Zostera marina community.
     pp. 518-540.  IN;  Cronin, L. E. (ed.).  Estuarine Research, Vol. I.,
     Academic Press, N.Y.  738 pp.

Valiela, I., J. M. Teal, and W. Sass.  1973.  Nutrient retention in salt
     marsh plots experimentally fertilized with sewage sludge.  Estuarine
     Coastal Mar. Sci. 1:261-269.

-------
             INTERACTIONS INVOLVING RESIDENT CONSUMERS
                  R.  J.  Orth  and  D.  F.  Boesch
Introduction


         One of the most notable features of SAV habitats is the


characteristically high density of animals residing in the grass bed.


This large standing stock of animals is thought to be fundamental to


the resource value of SAV beds.  The grass bed provides substrate,


protection and food resources which allow maintenance of high faunal


densities.  The protection provided by the bed and the high prey


density serve migratory utilizers of the SAV habitat, i.e. crabs,


fishes and waterfowl.


         The epifauna and infauna represent a diverse and complex


assemblage which includes micro- and macroalgae, protozoans,


polychaetes, oligochaetes, bivalves, decapods and barnacles.


Many of these groups exhibit distinct seasonal pulses of abundance


depending on their individual spawning periods (Stevenson and Confer,


1978).


         The biotic community within grass beds is quite distinct from


the communities in adjacent unvegetated areas.  Because of the lack of


suitable substratum, there is usually very little epifauna in bare


sand or mud areas.  These animals are primarily using the blades as a


substratum or in the case of herbivorous gastropods, grazing on the


microalgae that grow on the blades.


         The fact that the epifauna may not be totally dependent on the
                                                                 V

presence of grass but rather any substrate, biotic or abiotic, for its


survival, does not take away from the importance of the presence of the

-------
                                                                       45
grass itself.  The grass is a renewable resource, unlike many other




substrata, and provides a suitable substrate for growth every year.




In addition, the grasses serve other functional roles that are equally




important (e.g. erosion buffer, detrital source, nutrient pump), which




could not be achieved with an abiotic substance.




         The infaunal community is also quite distinct from that in




adjacent unvegetated areas.  There is a tremendous increase in numbers




of species and individuals in grass areas and this may be related to




increased sediment stability and/or microhabitat complexity of food




supply (Orth, 1977; Thayer, Adams and La Croix, 1975).  Orth (1977),




working with infauna of Chesapeake Bay eelgrass, found infauna to




increase in density and diversity from the edge of an eelgrass bed




to the center of the bed and also with increasing size of the bed.




He related this increase to the sediment stabilizing function of




eelgrass and showed that decreasing the stability of sediments




experimentally (removing blades of grass by clipping, simulating wave




action) and naturally [cownose ray activity (Orth 1975)] decreased




the density and diversity of the infauna.




         The motile community is also diverse and quite distinct from




surrounding unvegetated areas (Orth and Heck, unpublished; Kikuchi,




1974).  Hardwick (1973) found that on the West Coast, the herring,




Clupea harengus pallasi, used eelgrass leaves to lay most of their




eggs on.Though Clupea spp. on the east coast do not use grass beds like




the west coast species, the toadfish Opsanus tau uses the rhizomes as




attachment sites for its eggs.  Juveniles and adults of many species




may utilize eelgrass for protection.  The blue crab, Callinectes sapidus,

-------
                                                                       46
is found in greater abundance in eelgrass beds both as juveniles and




adults (Lippson, 1970, Orth and Heck, unpublished).  Changes in eelgrass




abundance are thought to be a factor in variations in the commercial




catch (W. A. Van Engel, personal communication).  Many species use SAV




habitats primarily because of the abundance of food.




         One of the more complete studies of fish communities of eelgrass




was done by Adams (1976a,b,c) in North Carolina.  He found the highest




fish biomass when temperature and eelgrass biomass were maximal.




Further, food produced within the grass bed could have accounted for




approximately 56% by weight of the diet of the fish community.  The




high fish production was due to juveniles which had higher growth




efficiences than older fishes.  They accounted for 79-84% of the




total annual fish production.




         By simply looking at the structural complexity of SAV habitats




one does not get an appreciation for the flow of energy needed to




support the complex trophic structure.  From analysis of feeding habits




of the higher level consumers (fish and crabs) it is obvious that




benthic invertebrates play a major role in the flux of energy through




the seagrass system.  The benthos represents the major link between




primary production, detritus, and higher trophic levels.




         The amount of energy or biomass produced within the system can




only be estimated by a detailed look at the secondary production of the




individual species inhabiting the grass bed.  Secondary production




estimates will provide the basis for determining the amount of energy




available and the rate at which it is transferred to the higher *




consumers.

-------
                                                                       47







         Although few marine organisms consume SAV directly, the SAV




resource is recognized as a preferred food for many waterfowl species




(Bent 1925; Cottam 1939; Cottam and Munro 1954).  The availability of




SAV fluctuates widely and is currently declining in the Chesapeake




Bay (Stevenson & Confer 1978, Bayley et al. 1978).  The impact of




such a decline on waterfowl depends on the degree of dietary




specificity.  While the abundance of SAV is presently inadequate




to totally support wintering waterfowl populations, it may be very




important early in the season.  The degree to which waterfowl use




this resource and possibly affect the ecology of SAV is poorly




understood.  Birds may utilize the limited resource for conditioning




and building of fat reserves to survive winter stress, when feeding




is more difficult.




         The general importance of seagrass beds in the marine and




estuarine environment has been well documented.  Although much work




has been done on the structural components of eelgrass beds in the




Chesapeake Bay, little information is available on the functional




ecology of these beds.




         Our efforts from July 1978 to the present have been directed




at determining the relative importance of SAV beds and understanding




the trophic role of resident consumers in such systems by:  a.)




determining the bases of secondary production; b.) quantifying secondary




production of important consumers; c.) determining which resident




consumers are trophically important to migratory consumers and d.)




determining the degree to which migratory consumers control populations




of resident consumers.

-------
                                                                       48
Methods and Materials



A.  Habitat Differences;




         Routine sampling was scheduledto coincide with major biological




events in the grassbed and adjacent areas.  These events included the




arrival of major predators in the system  (early spring), the partial




defoliation of Zostera (mid-summer), and  the major larval settling




periods (spring and fall).  Such timing,rather than quarterly sampling,




would yield the best data on the dynamics of the grass bed and adjacent




habitats.




         Three habitats were sampled five times (July and October, 1978




and April, June and August, 1979) to determine quantitative and




qualitative differences in their associated fauna.  The habitats




included an offshore sandbar system (outside sand), sandy patches




within the grass bed (inside sand) and the grass bed proper (Fig. 1).




Initially, 10 stations were established in each habitat.  Analyses of




data from the initial sampling indicated  that 5 rather than 10 stations




adequately represented the infauna in the two sand habitats.  One



                9                                  9
sediment (3.8 cnr) and three macroinfaunal (0.007 nr each) cores were




taken at each station.  Prior to taking infaunal and sediment cores




in the grass bed an epifaunal sample was  taken at each station by




clipping and collecting grass from the area to be sampled.  Coring




was then conducted within the clipped area.



         Vertical distribution of infauna was examined in July 1978.


                                                        2

A 35 cm long plexiglass core 9.4 cm in diameter (0.007 m ) was used to




collect infaunal samples.  One such core  sample was taken at each




station.  The top 10 cm of each sample was sectioned vertically into 2

-------
                                                                       49





cm intervals and the remaining material was divided into 5 cm intervals.




Based on these data, it was determined that a sample depth of 15 cm




adequately collected the infauna.




         Before sieving and preservation samples were held for at least




30 min. in labelled plastic bags containing isotonic MgCl2 as a relaxant.




This kept many of the smaller polychaetes and oligochaetes from crawling




through the sieve.  All infaunal samples were washed through 0.5 mm mesh




sieves and the retained material was preserved in 10% buffered seawater




formalin.  A vital stain (Rose Bengal) was added to facilitate laboratory




sorting.




         Epifaunal samples were collected by clipping plants to within




2-3 cm of the sediment surface and easing the blades into a collecting




bags with a 0.5 mm mesh bottom (Marsh 1973).  Samples were kept in




water and processed live by stripping all epifauna from the blades




and preserving them in 10% buffered seawater formalin containing the




vital stain Rose Bengal.  The remaining plant material was sorted




according to species (Ruppia, Zostera and algae), oven-dried at 80°C




for at least 48 h and then weighed to the nearest 0.1 g.






B.  Predator Exclusion Experiments;




         Exclosures consisting of large circular topless pens 5 m in




diameter (20 m^) and smaller, square cages (0.25 m2) were used in the




manipulative predator exclusion experiments.  One pen was constructed




in a mixed Ruppia-Zostera bed and another in an adjacent inshore sandy




area.  The pens were made of 4.3 m long salt treated wooden pilings




placed 1.5 m into the bottom.  Initially, thick-wall galvanized pipes




(240 cm x 2 cm) were placed between the equally spaced wooden pilings

-------
                                                                       50
to provide shape (   Fig. 1).  The pipes inadequately supported the




weight of the netting during storms and were later replaced with 10 cm




x 10 cm x 360 cm wooden posts.  Pens were encircled by a piece of




black plastic 0.63 cm mesh netting with a uv retardant (Conwed Corp.




Plastic Netting #OV3010).  The netting,which was 324 cm wide, was




attached to the posts at a height of 240 cm above the bottom.  Excess




netting was stapled along the bottom with 18 cm long wire staples to




form an 84 cm wide skirt which extended outward from each pen.  The




skirt prevented predators from burrowing into the pen.  An entrance




into each pen was constructed by sewing a 5 cm wide x 324 cm long




strip of VELCRO to one end of the netting with the opposing piece




attached to a piling.




         Smaller square cages measuring 50 cm on a side and 50 cm high




were constructed of reinforcing rod frames covered with the same




plastic netting as used on the pens.  Each cage had 30 cm long legs




which were pushed into the bottom, anchoring the cage.  A top attached




with VELCRO strips on three sides allowed easy access into each cage.




Panels simulating only the sides of cages were similarly constructed.




         Triads of experimental treatments were randomly arranged in




triplicate both within and outside of the pens in each of the two




habitats.  A triad consisted of three experimental treatments:  a




complete cage enclosing 0.25 rar of bottom area, and open cage with no




top and parallel sides of 0.25 nr, and an uncaged control area (   Fig.




1).  One of the three triads per experimental condition (sand; sand




plus pen; grass, grass plus pen) was designed to be destructively




sampled after an appropriate time interval.

-------
                                                                      51
Fig. 1.  Design of predator exclusion experiments showing the




         construction of the large pen and the placement of




         experimental triads.  Closed circles around the perimeter




         of the pen indicate the placement of pilings and open




         circles show the position of galvanized pipes which




         were later replaced by wooden poles.

-------
                                                                       52
         Sampling for predator exclusion work was scheduled to take




spring and fall larval sets into account.  Four sample times were




designated for 1979:  TQ - April; T^ - June; T2 - September; T3 -




November.  Infauna in both the unvegetated habitat and the grass bed,




and epifauna in the grass bed were collected and preserved using the




same methods described for routine sampling.  Ten core samples for




infauna and one grass clipping (vegetated area only) were taken when




each experimental area and treatment were sampled.




         Pen and cage effects were examined by placing larval and




sediment traps inside additional cages (sediment traps in sand area




only) to assess variations in larval recruitment and sedimentation




rates.




         Cages and pens were cleared of fouling organisms when necessary.




Crab pots and minnow traps were placed within pens to remove predators




which entered as larvae on juveniles.  Several blue crabs were also




removed by spearing.




         Two days prior to the first sampling period of 12 June, pens




were breached during a severe storm.  After sampling, pens were rebuilt




and a backing of heavier larger mesh (13 mm) netting (Conwed Corp.




Plastic Netting //OV1580) was added to the smaller mesh.  After the




first sampling period but prior to reconstruction of the pen, blue




crabs had burrowed into all sand cages.  Because of this disturbance




cages were removed and replaced by new ones positioned over bottom




which had been uncaged.  In addition, a 24 cm wide skirt was placed




around each sand area cage.

-------
                                                                       53
C.  Secondary Production;


         Eight consecutive monthly samples were taken for secondary


production using a suction dredge (Fig.2   ).  Quantitative samples


were collected from within a weighted plexiglass cylinder with a


diameter of 28.6 cm (0.065 m2) and a height of 65 cm.  The cylinder


was carefully placed over the grass blades and the sample was taken


from within by filtering water through a clear plastic bag with a


removable 0.5 mm mesh sieve bottom.  Samples of larger,more motile, or


widely spaced species were collected from within a weighted fiberglass

                                   r\
cylinder 110 cm in daimeter (0.95 nr1) and 30 cm high equipped with a


0.5 mm mesh screened top (Fig. 2  ).  All samples from the larger


fiberglass frame were filtered through a 1 mm x 1.5 mm mesh bag.


The sampling frame was dropped from a boat over dense vegetation.


Only drops over 100% vegetation cover were sampled.  The majority


of samples were taken from mixed Zostera-Ruppia areas where abundances


of vagile epifauna appeared to be the greatest.  Attached epifauna,


Crepidula plana, was sampled by clipping the grass from within a

     2
0.1 m  ring as close to the sediment surface as possible.  Grass


blades were then cleaned of all attached epifauna and saved for


future processing.  All samples for production estimates were


preserved in 10% buffered formalin.  Samples were sorted in the


laboratory and up to 200 complete individuals for each species were


measured, dried and weighed.  Based on their trophic importance to


higher level consumers 9 species were selected for production estimates:

-------
                                                                  54
Fig. 2 .   Schematic diagram of suction dredge sampler.   A




          venturi effect in the suction head draws the sample




          from within the sampling frame through the collecting




          bag.

-------
                                                                       55
Decapods                  Amphipods                Isopods




  Callinectes sapidus       Gammarus mucronatus      Erichsonella attenuata




  Crangon septemsplnosa     Microprotopus raneyi     Edotea triloba




  Palaemonetes vulgaris     Caprella penantis        Mysid




                                                     Neornysis americana




Presently 4 months of data have been worked up.  This report contains




information on growth rate and preliminary details of life histories.




Final estimates of production must wait until all the data are available.




Species need to be separated into cohorts or recruit groups if possible




for use of the instantaneous growth rate or removal summation methods




(Water and Crawford 1973), or combined into average cohorts for




production estimation by the Hynes method (Hamilton 1969).






D.  Tissue Samples;




         Tissue samples for the Carbon-Hydrogen-Nitrogen ratio, C  /C



               13
carbon ratio (6  C) and calorimetry were collected throughout the summer




of 1978.  Plant material was carefully checked for epiphytes or epifauna




which were removed by scraping or brushing prior to drying.  Benthos and




fish had their guts removed or were held in screened containers in




aquaria for 24 hr. to permit the voiding of gut contents.  Specimens




of resident consumers and predators were grouped by size.  A special




effort was made to examine changes in tissue chemistry with growth,




especially with regard to 6^-^C values.  Shelled animals were treated




with 10% HCl prior to analysis to remove shell fragments.  All tissues




collected were then dried, ground to a fine powder and distributed to

                                                                x


subproject principal investigators or consultants for further analyses.

-------
                                                                       56


E.  Stomach Analyses (Callinectes sapidus):

         Eighty-three blue crab stomachs were analyzed in 1978.

Individuals were collected with a 4.87 m  (16 ft) otter trawl with

19 mm (3/4 in) wings and a 6.3 mm (1/4 in) cod end liner.  The trawl

was pulled for a period of 2 min. at a speed of 2-3 knots.  Crabs

collected were subsampled and those selected were immediately weighed,

measured, sexed,    and the molt stage noted.  Stomachs were removed

in the field and preserved in 10% buffered seawater formalin with the

vital stain, Rose Bengal.  Each stomach was carefully dissected in

the laboratory and the contents enumerated and identified when possible.


F.  Waterfowl Interactions:

         A preliminary field effort was undertaken in 1978-1979,

consisting of 34 censuses and feeding observations between 16 December

and 22 March.  Birds were censused during daylight hours at approximately

3-hourly intervals on 6 days.  The remaining censuses were limited by

poor weather or other activities at the site.  Waterfowl were counted,

located by transect interval, and behavior was recorded as feeding or

non-feeding.



Results and Discussion

A.  Habitat Differences:

         Cumulative species curves for vertically sectioned cores from

each habitat (Fig. 3  ) flattened at a depth of approximately 15 cm.

Most species in each habitat were found in the top 15 cm of sediment
                                                                %
but the composition and numbers of individuals of the dominant taxa

differed from one area to the next (Table 1 ).  A greater number of

-------
                                                                     57
Fig. 3.  Cumulative species curves of vertically sectioned cores




         from three habitats.

-------









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-------
                                                                      59




individuals per section were found in the grass bed below the top 2 cm


than in the other two habitats (Table 3 ).  It is possible the grass


bed afforded some degree of protection from predators or the root and


rhizome mat provided a food source supporting a greater number of


infauna than unvegetated habitats.

                                                                   2
         Generally twice as many infaunal species per core (0.007 m )


were associated with the grass bed than were found in the adjacent sandy


habitats (   Fig. 4 ).  An average of 21 infaunal species per core were


found in SAV beds 'where only 9 were associated with sand patches within


the grass bed:and 7 were found in the offshore sand bar area.


         With the exception of the July (1978) sample date, there were


also a greater number of individuals per nr in the grass bed than in


either of the sand areas due in part to the relative stability of each


habitat (   Fig.5  ).  The reversal in this trend during July was due

                                                    2
to a large set of the bivalve, Gemma gemma (32,648/m ).  By the next


sample date they had greatly declined in abundance.  In addition to


sediment stability, the refuge factor and structural complexity of


seagrasses may be a cause for the greater abundance of grass bed fauna.


         In October, 1978 and June, 1979 Zostera had a greater number


of epifaunal individuals per gram of grass than either mixed Zostera-


Ruppia (where both species contribute at least 15% to the sample


biomass) or Ruppia (   Fig.6  ).  However, in April, 1979, Ruppia


contained almost two orders of magnitude more individuals than Zostera.


During July, 1978 individuals per gram of grass were more equitably


distributed between the three areas of the grass bed.  There is little


doubt that in vegetated areas the increased habitat complexity and

-------
                                                                      60
Fig. 4.  Mean number of infaunal species/core (0.007 m^) from the




         three habitats found during routine sampling.

-------
                                                                      61
Fig. 5.   Mean number of infaunal individuals/m^ from the three




          habitats found during routine sampling.

-------
                                                                      62
Fig. 6.   Mean number of epifaunal individuals per gram of grass found




          during routine sampling.

-------
10.000-r
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           Zostera
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October 1978
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                                      I
                                              L-J*
lun*
    19/V

-------
                                                                          63

surface area provided by the grass blades significantly enhances the

number of species inhabiting the area.

     From an analysis of fish gut contents, it appears that the

epifauna are an important link in transferring energy from primary

producers and decomposers:  to higher trophic levels.  For example, spot

(Leiostomus xanthurus) fed primarily on epifaunal organisms (amphipods,

polychaetes) or those species associated with plant detritus at the

sediment surface (copepods, nematodes, ostracods) (see Merriner and

Boehlert, this report).  Few truly infaunal species were consumed.  Spot

have a "vacuum cleaning" mode of feeding where an individual moves along

a grass blade or the sediment surface ingesting food items and detritus

and may significantly influence structure of the epifaunal community.

Spot appear to have difficult foraging on the bottom in dense vegetation.

     Late juvenile and early adult silver perch (Bairdiella chrysoura)

feed exclusively on motile and vagile epifauna (see Merriner and Boehlert,

this report) by visual cues and may also effect epifaunal community

structure.  Bairdiella first appears in the bed in August as juveniles and

remains until water temperatures drop in the fall.  The most frequent preyed

upon food item, mysid shrimp, also make their appearance in the early

fall.  Other food sources, the majority of which are amphipods and

isopods, are permanent residents in the grass bed.

     Pipefish (Syngnathus fuscus) are also trophically important in

grass bed ecosystems.  This species forages by sight among grass blades

and feeds primarily on epifauna (see Merriner and Boehlert, this report).

Principal food items included calanoid copepods, mysids, and amphipods.
                                                                    *
Mysids (Neomysis americana) were more frequently consumed in October 1978,

when they were more abundant in the grass bed.  Capiellid amphipods were

also a common food item.

-------
                                                                       64
B.  Predator Exclusion;

         Initial results of predator exclusion experiments suggested

that 1) predation plays an important role in structuring the benthic

communities in grass bed areas and 2) that predation may have a greater

impact on community associated with unvegetated habitats than grass

beds.

         There were more species and individuals in the sand area cage

treatments for both the penned and unpenned conditions after 2 months

of caging with no consistent patterns in the vegetated area for similar

treatments (   Figs. 7  and 8 )•  However, the abundance of infauna in

the vegetated area was initially much higher than in unvegetated areas.

In June 1979 vegetated areas contained 5 to 10 times the number of

individuals found in adjacent sand patches.  The abundance of indi-

viduals and numbers of species in the caged sand area was similar to

the untreated vegetated areas although differences in the species

composition did exist.  Mya arenaria, the soft shell clam, was

extremely abundant in the caged sand area (.   Fig. 9 ) but its

abundances were much lower in the grass area.  The caged sand

community developed only after two months, primarily by recruitment

from planktonic larvae>whereas the grass infaunal community represented

an older,more established community which had developed from the

start of the growing season.
                                                                v
         Based on this preliminary data, we suggest that the infauna in

sandy areas was more susceptible to predation.  Their response to

-------
                                                                       65
Fig. 7.  Total number of individuals per core for each treatment




         (S = sand area; M = mixed grass area; OC = cage with two




         sides only; C = complete cage; P = pen.  e.g. I'B-P+C =




         complete cage treatment located inside the pen in the




         grass bed).

-------
                                                                  66
Fig. 8.  Total number of species found in five cores for each




         treatment (see      Fig. 7 for treatment designation).

-------
                                                                     67
Fig. 9.  Total number of Individuals of the soft shell clam,  Mya




         arenaria, in five cores, for each treatment.

-------
                                                                       68
protection was most pronounced.  The infauna of the more spatially


diverse grass area are protected in part by the roots and rhizomes


and respond less dramatically .  This community may already be near


maximum densities.


         Predator exclusion studies conducted both in the Chesapeake


Bay and Europe have shown similar patterns of community response


(Virnstein, 1977; Reise, 1976; Orth, 1977).  However, our data only


represent one sampling period and definitive habitat comparisons


and species response patterns will be discussed in detail following


the end of the experiment.


         Data for the grass bed epifauna (Table 2) are also preliminary.


Uncaged treatments contained a greater abundance of individuals than


caged treatments due to fewer barnacles, Balanus improvisus, in the


caged areas, both within and outside the pen.  Observations of barnacle


set on the sediment traps placed in the sand area suggested fewer


barnacles set inside than outside the cages.



C.  Secondary Production;


         The various methods of production estimation are sensitive to


growth type (Water 1977).  To accurately estimate production it is


therefore necessary to know the type of growth exhibited by a species.


Growth is basically the process of increasing mass in developing


organisms and involves following changes in body weight or some


measure proportional to weight.  We have chosen to measure the


lengths of various parts for the 9 species and have calculated the
                                                               v

relationship between length and weight (Table 3).  Gammarus was the


only species to exhibit isometric growth (weight increased as the cube

-------
                                                                    69
Table 2.  Numbers of epifaunal species and individuals per gram of
          SAV for each treatment in the predator exclusion experiment
          taken in June, 1979.

Balanus improvisus
Bittium varium
Polydora ligni
Erichsonella attenuata
Gammarus mucronatus
Crepidula convexa
Caprella penantis
Astyris lunata
Cymadusa compta
Nereis succinea
Styllochus ellipticus
Anadara trans versa
Ilyanassa obsoleta
Urosalpinx cinerea
Mya arenaria
Idotea baltica
Mytilus edulis
Triphora nigrocincta
Heteromastus filiformis
Ampithoe longimana
Doridella obscura
Ampithoe valida
Palaemonetes sp.
Sabellaria vulgaris
Brania clavata
Nemertean
Nudibranch
Hit re 11 a lunata
Microprotopus raneyi
Edotea triloba
Paracaprella tenuis
Odostomia bisuturalis
Number of Species
Number of Ind./g. SAV
M
180.0
2.8
3.7
4.2
4.6
9.7
0.9
1.6
0.2
0.7
0.2
0.5
0.2
0.9
0.2
15
210.4
MfOC
135.6
4.3
3.9
2.2
2.4
15.9
0.6
0.2
0.7
4.3
1.2
10
170.1
W-C
118.5
6.4
9.4
1.2
0.6
9.9
0.1
0.1
0.4
1.0
0.6
0.1
0.1
13
148.5
MfP
324.3
3.0
2.2
10.1
1.8
9.1
1.0
0.8
1.4
2.7
0.2
0.2
0.6
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.3
21
359.1
MfP+OC
166.4
3.6
7.4
11.0
5.0
10.0
1.1
1.5
2.0
1.1
1.2
0.1
0.1
0.1
•- 0.4
2.1
0.1
0.1
0.1
19
213.4
MfP+C
104.7
0.7
6.4
1.4
1.0
9.6
0.2
0.4
0.1
1.1
1.7
0.1
0.4
0.2
0.2
0.2
0.1
0.1
0.1
19
128.7

-------
                                                                                                                                    70
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-------
                                                                       71
of length).  Allometric growth (weight did not increase as the cube of




length) was exhibited by all other species.  The weight of Neomysis




increased faster than the cube of length whereas the opposite was true




for the remaining species.




         While working up the samples we noticed that species might be




growing at different rates in pure Zostera, pure Ruppia or mixed




Zostera and Ruppia stands.  Analysis of covariance was used for




determining significant differences in growth rates between these




three habitats (Table 4).  Significant differences were found between




habitats for Erichsonella and Neomysis.  Erichsonella, an isopod of




limited mobility, grows larger in Zostera.  Neomysis, a motile mysid




shrimp, grows larger in mixed stands.  Presently we are not certain




what causes these growth differences but they may be related to:  1)




the differential occurrence of a preferred food source in one habitat




or 2) predatory cropping of larger older individuals.  For Neomysis




it may also be related to a refuge function since the species is very




motile and may seek mixed stands to hide in since they tend to be




denser than pure stands.









                           Life History




         The life history of a species greatly influences its annual




production.  For marine invertebrates the number of generations/year,




maximum size, life span, and time spent in the plankton as larvae are




most influential.  We will not know what many of these values are for




our selected species until a year's data are worked up, but fortthe




first 4 months from April to July we have some approximations (Table 5).

-------
                                                                       72
Table 4.  Analysis of covariance of growth rates between habitats.
Probability Habitats*

Decapods
Callinectes sapidus
Crangon septemspinosa
Palaemonetes vulgaris
df

2
2
2
F

2.15
0.61
2.26
of >F

0.12
0.55
0.12
compared

Z,M,R
Z,M,R
Z,M,R
Amphipods
     Caprella penantis
Gammarus mucronatus
Microprotopus raneyi
Isopods
Erichsonella attenuata
Edotea triloba
2
1

1
1
1.29
0.72

5.90
1.26
0.28
0.40

0.02
0.27
Z,M,R
Z,M

Z,M**
M,R
My s ids
     Neomysis americana
19.82
0.0001
Z,M,R**
*  Z = Zostera. R = Ruppia. M = mixed Z and R

** significant difference

-------
                                                                         73
Table 5.  Some life history parameters for secondary production species
          from April to July.

Decapods
Callinectes sapidus
Crangon septemspinosa
Palaemonetes vulgaris
Amphipods
Caprella penantis
Gammarus mucronatus
Microprotopus raneyi
Isopods
Erichsonella attenuata
Edotea triloba
Maximum
size
(mg)
6574.0
130.00
142.00
3.10
6.20
0.11
6.90
3.00
e QJ <"*
•H N 00
C -H 6
g cn^
4.00
1.00
11.00
0.01
0.01
0.04
0.10
0.10
Cohort or
generations
to date
1
1
2
2
2
2
2
2
mobility
good
good
good
limited
?
7
limited
limited
feeding
type
predator
omnivore
omnivore
predator
herbivore
herbivore
herbivore
herbivore
Mysids
   Neomysis americanus
5.00
0.01
good
omnivore

-------
                                                                       74




While it is too soon to determine life span it appears that the



amphipods and isopods live about 4 months.  No determination for



the life span of the other species can be made at this time since a



complete generation or cohort has not appeared or disappeared within



the 4 months of data analyzed.  At least 2 cohorts have appeared for



all amphipods and isopods.  Only 1 cohort is present for Callinectes



and Crangon.  Palaemonetes is the only decapod with 2 cohorts present



(Table 6) .  Neomysis was found only in April.   Through July it had



not reappeared in the secondary production samples but was taken in



June from the sand bar habitat.





                            Production



         Both the instantaneous growth method, which basically sums



growth increments, and removal summation method, which sums increments



of mortality, will be applied for production estimates for species with



definable cohorts (Waters 1977, Crisp 1971).  The Hynes method will be



applied to species which cannot be separated into cohorts after analysis



of 12 months of data (Hamilton 1969).  To date cohorts can be recognized



only for Callinectes, Palaemonetes, Microprotopus, Erichsonella and



Edotea.



         The most complete cohort recognized to date is cohort 1 for



Erichsonella which will be used as an example to calculate production



(Table 7).  These production values are for one generation or cohort



of Erichsonella and represent only a fraction of the annual production.


                                                             2
The difference between the removal summation (0.63 g dry wt/m ) and


                                     0                         *•
instantaneous growth (0.56 g dry wt/nr) is due primarily to not having



sampled the early part of the cohort in March and possibly February.

-------
75


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-------
76





































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                                                               77
Table 6 (continued)

P. vulgaris
0-1 nun
1-2
2-3
3-4
4-5
5-6
6-7
7-8
8-9
9-10
Cohort 1
Cohort 2
April




.22
.38
.11
.11



.82

May




1.14
1.86
1.24
.72
.31
.21

5.48

June





6.08
.82
5.96
7.95
.82

21.63

July


.13
.13
.13
5.35
2.22
2.35
2.35
.65

10.81
.39
* cohorts not distinguishable.

-------
                                                                    78
Table 7.  Production calculation for one cohort of Erichsonella from
          April to July.
Removal Summation Method



April
May
June
July

No./m2

112.2
443.5
46.1
3.8
w1
(mg)

1.13
2.18
2.99
3.98

No. Iost/m2 x2

-331.3
397.4
42.3

wt . at =
loss
(ing)
1.66
2.57
3.49

= Production
(mg/m2)

-549.96
1029.27
147.42

                      0.63 g dry wt/zn2
                                                       626.73
Instantaneous Growth Rate



April
May
June
July
Standing
Crop
(mg)
126.50
964.67
137.63
15.12
-1 L
w G4 x
(mg)
1.13 0.66
2.18 0.32
2.99 0.29
3.98

B
(mg/m2)
545.59
551.15
76.38


P
(mg/m2)
360.09
176.37
22.15

                          0.56 g dry wt/m
                                                 558.61
  w"
=  mean individual weight - calculated from length-weight
   regression and size frequency distribution
  number of individuals lost between sample dates

  weight at loss as average of v7  for two consecutive sample dates
  G = instantaneous growth rate as In

-------
                                                                    79
Thus for the one cohort of Erichsonella approximately 0.56 to 0.63 g

        /\
dry wt/m^ of tissue were produced and available for consumption by


other trophic levels, which could be either higher level consumers


or lower level decomposers .  Assuming this cohort of Erichsonella


occurred and produced evenly over the entire grass bed (140 hectares)


then 782 to 877 kg of dry tissue were available to other trophic levels.


When more data become available from feeding habits studies of higher


level consumers it will be possible to determine what fraction of the


secondary production is utilized.
D.  Tissue Samples


         A preliminary analysis of 6-^C ratios in some floral and faunal


components of the SAV habitat (   Table 8) revealed similar values to


those found by Thayer et al. (1978).  Spyridia filamentosa, a macro-


epiphyte on Zostera and Ruppia had 6^C values of -17.7 which were


similar to Zostera epiphytes (-16.3) in North Carolina (Thayer et al.,


1979) .  Some of the dominant faunal components had values ranging from


-13.3 (Penaeus aztecus) to -15.4 (Syngnathus fuscus) .   Although


additional components of the grass bed await examination it appears


those analyzed to date may be linked more directly to a plankton-carbon


food chain than to a seagrass-carbon system.  These findings are in


agreement with those of Thayer et al. (1978) who examined trophic


relationships in a relatively young eelgrass bed.



E.  Stomach-Analyses (Callinectes sapidus) :


         The masticatory mode of feeding made the identification of gut


contents to the species level difficult.  Percent frequency of occurrence

-------
                                                                    80


        Table 8.   513C Values in SAV Systems
                                      Values
                          Thayer. G. W.  et  al. ,  1978     VIMS

Zostora marina (live)              -10.2
.£• n'a r. .* "-**  (dead)                    -10.6

7.. marjnrt  cplphytcw                -16.0
   r Idl/i  f I I .niicnt tmi                  -                 -37.7
Suspended  particulates             -20.0

Palaeroonetes  vulgaris              -16.3                -14.9
Cran^'Mi scptemspinosa                 -                 -14.5
Callinectes sapidus                   -                 -13.8-
Penaeus aztecas                       -                 -13.3

B.I! nlh-l la cliryiuira                -]6.8                -Jr>.2
Lc-i(i:.t()Mius xaiiihurus                  -                 -15.2
Syn^nathus fuse us                  -17.0                -15.4
           f T oridae                -15.3
Illy anassa  oh.solct_a_                   -                 -14.0
Nassarias vibex                    -15.4

-------
                                                                     81
of food item indicated that blue crabs feed on both epifaunal and


infaunal species (   Fig.10 ).  Zostera was found in 70% of the


stomachs analyzed.  Generally, live,intact,and very uniformly cut


sections of leaf material were present,indicating that crabs may


ingest the blades but digest only the encrusting organisms.  Epifaunal


molluscs, isopods and Balanus improvisus were among the major food


items in crab stomachs.  Callinectes also foraged among the root and


rhizome mat on infaunal molluscs.  Feeding burrows and infaunal


feeding were frequently observed in the field.  Callinectes may be


an important predator on the infauna in vegetated habitats.  In


addition to nutritional needs derived from the grass beds, crabs


also utilize these habitats for protection from predators during


the critical soft shell phase of the molt cycle.



F.  Waterfowl Interactions:


         The Canada goose was the most abundant waterfowl species,


averaging 556 individuals per census date and exceedtig 2000 individuals


in one census (Table 10).  Second in abundance were redheads.


     present primarily at dawn and dusk.  This species probably foraged


in the grass beds nocturnally and were inadequately censused.


         Buffleheads (Bicephala albeola) consistently utilized the area,


and averaged 44 birds per day.  Brant were abundant only on one census


date.  Whistling swans, red-breasted mergansers (Mergus serrator), and


widgeons (Anas americana) were regularly encountered in low numbers.


         Canada geese and redheads showed differential habitat use
                                                                 i,

(   Fig. ll).  Canada geese, which forage by tipping up rather than


diving, avoided the deeper areas (>60-80 cm).  At tide levels above

-------
                                                                    82
Fig. 10.  Percent frequency of occurrence of food items in Callinectes




          sapidus stomachs.

-------
                                                                                                                                                    83
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-------
                                                                     84
Fig. 111.  Distribution of dominant waterfowl  species  at  the study




          site.

-------
                                                                     85





MLW, goose foraging is restricted to an average of 40-50% of the




vegetated area throughout the grass bed.  The relationship between




tide level and numbers of foraging geese further emphasizes the




influence of water depth (   Fig.12 ).  Redheads, which are diving




ducks,were censused in deeper water, and may have utilized the same




areas for nocturnal foraging.  Diving buffleheads were not restricted




to shallow water, and were more evenly distributed although they




showed a slight preference for deeper water (   Fig.12 ).  Reduced




foraging in the shallowest areas (E-F) may relate to timing of field




observations.  Grass in the shallows may have been depleted early in




the season, when observations were not made.




         Preliminary work indicated consistent utilization of the grass




bed by Canada geese, redheads, buffleheads and red-breasted mergansers.




However, degree of trophic support can be assessed only by comparing




estimates of consumption with known dietary requirements, and the




work proposed for the 1979-80 season will emphasize this approach.




Several techniques including the use of exclosures, intensive censusing,




gizzard content analyses, and changes in S-^C values of liver tissue




will be used to quantify the utilization and importance of SAV to




waterfowl.

-------
                                                                86
Fig. 12.  Numbers of feeding vs. non-feeding Canada geese in




          relation to tide level.

-------
                            References
Adams, S. M.  1976a.  The ecology of eelgrass Zostera marina  (L.)>
         fish communities.  I.  Structural analysis.  J. Exp. Mar.
         Biol. Ecol. 22:269-291.

Adams, S. M.  1976b.  The ecology of eelgrass, Zostera marina (L.),
         fish communities.  II.  Functional analysis.  J. Exp. Mar.
         Biol. Ecol. 22:293-311.

Adams, S. M.  1976c.  Feeding ecology of eelgrass fish communities.
         Trans. Amer. Fish. Soc. 105:514-519.

Bayley, S., V. D. Stotts, D. F. Springer, and L. Steenis.  1978.
         Changes in submerged aquatic macrophyte populations at the
         head of Chesapeake Bay, 1958-1975.  Estuaries l(3):73-84.

Bent, A. C.  1925.  Life histories of North American wildfowl.  U. S.
         Nat. Mus. Bull. 130, part II., pp. 281-293.

Cottam, C.  1939.  Food habits of North America diving ducks.  U.S. D.A.
         Tech. Bull. No. 643.

Cottam, C. and D. A. Munro.  1954.  Eelgrass status and environmental
         relations.  J. Wildl. Mgt. 18(4):449-460.

Hamilton, A. L.  1969.  On estimating annual production.  Limnol. and
         Oceanogr. 14:771-782.

Hardwick, J. E.  1973.  Biomass estimates of spawning herring Clupea
         harengus pallasi, herring eggs, and associated vegetation in
         Tomales Bay.  Calif. Fish & Game 59:36-61.

Kikuchi, T.  1974.  Japanese contributions on consumer ecology in
         eelgrass (Zostera marina L.) beds, with special reference
         to trophic relationships and resources in inshore" fisheries.
         Aquaculture, 4:145-160.

Lippson, R. L.  1970.  Blue crab study in Chesapeake Bay, Maryland.
         Final Progress Report, NRI Ref. No. 70-46.  Univ. Md.

Marsh, G. A.  1973.  The Zostera epifaunal community in the York River,
         Virginia.  Chesapeake Sci. 14:87-97.

Orth, R. J.  1975.  Destruction of eelgrass, Zostera marina, by the
         cownose ray, Rhinoptera bonasus, in the Chesapeake Bay>
         Virginia.  Chesapeake Sci. 10:205-208.

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                                                                     88
Orth, R. J.  1977.  The importance of sediment stability in seagrass
         communities.  In; Ecology of Marine Benthos, B. C. Coull
         eds., Univ. of South Carolina Press, Columbia, South
         Carolina, pp. 281-300.

Reise, K.  1978.  Experiments on epibenthic predation in the Wadden
         Sea.  Helgolander wiss. Meeresunters. 31:55-101.

Stevenson, J. C. and N. M. Confer.  1978.  Summary of available
         information on Chesapeake Bay Submerged Vegetation.  U.S.
         Dept. of Interior, Fish and Wildlife Service.  FWS/OBS-78/
         66, 335 pp.

Thayer, G. W., S. M. Adams & M. W. LaCroix.  1975.  Structural and
         functional aspects of a recently established Zostera marina
         community.  Estuarine Res. 1:518-540.

Thayer, G. W., P. L. Parker, M. W. LaCroix and B. Fry.  1978.  The
         Stable Carbon Isotope Ratio of Some Components of an Eelgrass,
         Zostera marina, Bed.  Oecologia (Berl.) 35, 1-12.

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

Waters, T. F.  1977.  Secondary production in inland waters.  Adv.
         Ecol. Res. 14:91-164.

Waters, T. F. and G. W. Crawford.  1973.  Annual production of a stream
         mayfly population: a comparison of methods.  Limnol. and
         Oceanogr. 18:286-296.

Wood, E. J. F., W. E. Odum, and J. Zieman.  1969.  Influence of sea-
         grasses on the productivity of coastal lagoons.  Lagunas
         Costeras, un Simposio. Mem. Simp. Intern. Lagunas Costeras.
         UNAMVNESCO., pp. 495-502.

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                     HIGHER LEVEL CONSUMER INTERACTIONS




                      J.V.  Merriner and G.  W.  Boehlert






                               INTRODUCTION




      The  basic objectives  within this subtask of the  grant  are to  analyze




 the structural and  functional ecology of fish communities  in submerged




 aquatic vegetation  (SAV)  and to assess the importance of SAV to the




 production and maintenance of important commercial  fish  populations.  Our




 approach  has  been to combine a program of  field  sampling with laboratory




 study.  Areas to  be addressed include the  processes of recruitment and




 emigration from the SAV areas, the relative benefit of SAV  from trophic




 and refuge standpoints,  the effects of major  predators which may frequent




 the SAV areas,  biomass  estimates of the components  of the  fish community,




 the sources of  production  consumed by the  fish populations,  and ultimately,




 the levels of secondary production by the  fishes.




      The  fish community in the present study  divides  to  three components;




 these are i)  fish eggs,  larvae, postlarvae, and  pelagic  juveniles, ii)




 resident  fishes,  and iii)  migratory predators.   Ecology  of  resident fish




 communities in eelgrass  (Zostera marina) beds has been studied in  the




 Beaufort,  North Carolina area (Adams 1976a, b);  species  composition of




 the benthic fish  community in the study site  used in  the current work




 has been  qualitatively  described (Orth and Heck, in press).   The dominant




 resident  species  in the lower Chesapeake Bay  eelgrass bed was spot




(Leiostomus xanthurus), contrasting with the North Carolina  eelgrass fish




 community, where  pinfish (Lagodon rhomboides) and pigfish  (Orthopr^stis




 chrysoptera)  were the dominant species (Adams 1976a).  Analysis of




 feeding behavior  in the current study will allow determination of  the




 trophic interrelationships and the effects on secondary  producers  within

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                                                                        90
the system.  Mld-and late-summer gill netting also revealed certain of the




migratory predators (Orth and Heck, in press), including the sandbar




shark (Carcharinus milberti) and bluefish (Pomatomus saltatrix).  Preliminary




evidence suggested that these predators were feeding in the eelgrass




area.  In other parts of the lower Chesapeake Bay, the cownose ray




(Rhinoptera bonasus) has been shown to feed and have dramatic effects in




eelgrass beds (Orth 1975).




     Previous characterizations of Chesapeake Bay ichthyoplankton assem-




blages (Pearson 1941; Dovel 1971; Olney 1978) have concentrated on mid-




channel portions of the estuary and have neglected the generally




inaccessible nearshore, shallow environments.  As a result, the extent




to which Chesapeake Bay fish stocks utilize these nearshore zones as




spawning and/or nursery sites is unknown.  This lack of data takes on




added significance as a result of the recent emphasis on the importance




of shallow seagrass beds as refuge and feeding grounds for many species




of marine and estuarine fishes (Ried 1954; Adams 1976a, c).  The




greater utilization of vegetated over unvegetated habitats by juveniles




and adults of many species of fishes is well documented (Briggs and




O'Connor 1971; Orth and Heck, in press); the current study will document




the importance of these areas to the early life history stages of




fishes and will determine the time of immigration and residence for the




important species.  The contribution of zooplankton derived from sources




outside the vegetated areas will also be analyzed in the present study.

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                                                                        91
                          MATERIALS AND METHODS


Field Sampling


     The field sampling is conducted at the Vaucluse Shores study site,


north of the channel of Hunger's Creek (Figure 1).  Sampling of relatively


large areas is required for adequate estimations of fish densities; for


this reason our sampling areas are not distinctly defined with respect to


vegetation type.  Sampling is divided to three areas, designated as


representative of Zostera marina, Ruppia maritima, and an adjacent un-


vegetated area.  The nominal Zostera area is located between the sandbar


and land, along transect A.  The nominal Ruppia area is located on and


northeast of transect C.  The unvegetated sampling area is on the sandbar


west of transect markers B and A in depths appropriate for the particular


sampling gear.  As is apparent in vegetation maps of the bed, the nominal


sampling areas for Ruppia and Zostera contain mixed stands as well as pure


stands of the respective vegetation  types (Figure 1).  Differences noted


between the two sampling areas may therefore represent faunal changes


due to isolation from deeper water rather than differences attributable


to vegetation type.


     Sampling gears generally break down to those for 1) ichthyoplankton

and zooplankton, 2) resident fishes, and 3) migratory predators.  A


variety of gears were tested for sampling these components of the fauna


during the first six months of the project.  Ichthyoplankton and zooplankton


were initially sampled with towed, bridled nets; these were abandoned due


to excessive disturbance ahead of the net from the outboard motor which

                                                                   v
resulted in avoidance by fishes and samples with excessive silt, detritus,


and dislodged vegetation.  Resulting samples were often impossible to

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                                                                            92
Figure 1:  Vaucluse Shores study site.   Location of the vegetation types  are
           shown.

-------
R = RUPPIA
Z = ZOSTERA
S=SAND
/ = MIXED
  = TRANSECTS
CHESAPEAKE
    BAY
    M

-------
                                                                        93
preserve and sort (especially zooplankton samples with large amounts of

sand).  Routine sampling for ich- and zooplankton currently consists

of two replicate collections in each habitat  (Zostera, Ruppia, and sand)

utilizing a pushnet (Figure 2) constructed of h" diameter galvanized

pipe and deployed over the bow of a 19 foot outboard craft.  The frame

is equipped with a 1 meter ichthyoplankton net (505 Mm mesh) and two

18.5 cm zooplankton (202 ym mesh); the ichthyoplankton net and one zoo-

plankton net are fitted with calibrated General Oceanics flowmeters to

assess the volumes of water filtered.  Nets are fished at high tide for

2-3 minutes depending on abundance of plankton.  The sampling duration

and boat speed allows the ichthyoplankton net to cover 74-174 m2 of sea

surface and filter from 68-117 m3 of water.  All samples are taken in

the bed at high tide; routine monthly sampling is conducted at night;

daylight samples are taken at high tide in selected months.

     Each time the net is deployed, one ichthyoplankton and two zoo-

plankton samples result.  One of the zooplankton samples is preserved

in 10% formalin for later taxonomic analysis and estimation of abundance;

the other is washed with distilled water, frozen in the field on dry ice,

lyophilized, weighed, and ashed in a muffle furnace (6 hours at 500°C)

to determine organic biomass per unit volume.  Ichthyoplankton samples

are preserved in 5-10% buffered formalin.  In the laboratory they are

whole sorted for all fish eggs, larvae, postlarvae, juvenile, and adult

stages.  Specimens are later identified to the lowest taxon possible,

measured, and curated.
                                                                  v
     For sampling resident fishes, a portable dropnet similar to those

described in Moseley and Copeland (1969) and Adams (1976a) was built;

-------
                                                                            94
Figure 2:  Zoo- and ichthyoplankton sampling pushnet.   A. Gear array.  As
           presently designed, the net is fished with three nets.  The central
           net (505 urn mesh) is designed to sample ichthyoplankton and larger
           components of the demersal plankton.  The smaller two nets, fished
           at a depth of approximately one meter, sample zooplankton (202
           urn mesh).  B. Design of the net frame.  The gear is designed to
           fish off the bow of the boat prior to any bow wake; the nets
           trail under the hull of the boat.  The frame pivots onto the boat
           to allow access to the cod ends and ease in sample processing.

-------
k
)
>
1






202 M
NET
< 70cm >
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METER
NET

23cm



202 M
NET


B
                         Figure  2

-------
                                                                        95
it covered an area of 9.3 m  .  Our initial experiences with this gear

proved it to be unsatisfactory due to the small area covered, long deployment

times, and instability in rough weather.  We therefore abandoned the dropnet

in favor of a 40 m long, 2.4 m deep seine (Figure 3) fished in the manner

described for long haul seines by Kjelson and Johnson (1974).  Briefly,

the seine is deployed bag end first from the bow of an outboard craft

travelling in reverse.  The net is set in a circle and the long wing

pulled past the bag end to decrease the circumference of the circle to

approximately 7.3 m, after which the bottom of the net is closed off

by tightening a purse line.  The catch remains in the pursed section of net

and is brought on board the boat for processing.  When set in an ideal

circle, this gear encompasses an area of 127 m2.  Duplicate or triplicate

samples are taken monthly (from March through November) in each of the

three habitats.  Daylight samples are also taken in selected months for

diel comparisons.  Large specimens are identified, measured, and noted

on the field sheets; the remainder of the catch is preserved in 10%

buffered formalin for later identification in the laboratory.

     Migratory predators are sampled in gill nets.  Monthly sampling

consists of deploying 30.5 meters each of 12.7 and 17.8 cm stretch mesh

gill net perpendicular from shore in each of the three sampling habitats.

These nets are fished every four hours over a 24 hour period.  At each

sampling time, the catch is removed, identified, measured, and weighed,

and the net is reset.   Observations are made on relative fullness of

stomach contents and selected stomachs are removed and preserved for
                                                                   t
analysis of contents.   As with other collections, additional information taken

at the time of collection include date, time, habitat,  tide stage, depth,

water temperature, salinity, dissolved oxygen, and comments on weather.

-------
                                                                            96
Figure 3:  Haul seine used in the collection of resident fishes;  mesh size
           is 3.2 mm (square) throughout.  The net is set from the bow of
           an outboard craft travelling in reverse.  The short wing and bag
           end (a) is set first and the net paid out in a circle.  After the
           circle is closed, the long wing end; (b) is pulled past point "a"
           until reaching the last 7.3 meters of net.  The remaining circle
           is then pursed with the purse rings in this section of net and
           the catch brought on board the boat.

-------
Figure 3

-------
                                                                        97
Laboratory Procedures

     To determine the feeding behavior of the fishes and their impact upon


the resident secondary producers, stomach contents and feeding periodicity

studies are being conducted.  The resident fishes are collected by trawl

during the times of day when feeding is actively occurring for taxonomic

analysis of stomach contents.  For determination of feeding periodicity,

trawling was conducted over 24 hour periods in May and August 1979.  Stomachs


from the larger, migratory predators are sampled during the monthly gill

net collections.

     The method of stomach collection depends upon the size of the fish.

For resident fishes larger than 150 mm and for all migratory predators,

stomachs are removed in the field and preserved in 10% buffered formalin


immediately after capture.  Tags are placed with the stomach describing

fish length, species, and collection number to associate the stomach with


further information available on the field data sheets.  For resident

fishes smaller than 150 mm, specimens are preserved whole in 20% buffered

formalin; the body cavity is slit to facilitate penetration of the formalin.


When stomachs are removed a qualitative index of fullness based upon the

size of the specimen is assigned.  Contents are transferred to 40%

isopropyl alcohol prior to analysis.


     Analysis of stomach contents of planktivorous and piscivorous fishes

is conducted by the Higher Level Consumer Interactions group; identification

of stomach contents of fishes feeding on invertebrate secondary consumers

is conducted by the Resident Consumer Interactions group.   When contents

                                                                  \
are removed, a second qualitative index of the state of digestion of the


food items is determined.  The combination of these two indices allows

-------
                                                                       98
preliminary analysis of feeding periodicity.  After contents are identified

to the lowest taxon possible, individual food items are dried to constant


weight at 56°C and weighed.  Certain items, such as nematodes and


harpacticoid copepods are assigned weights from literature values for


dry weight.  Feeding of zooplanktivorous fishes will be conducted in the


coming year using the technique of Carr and Adams (1972).


     Feeding periodicity is being determined for spot (Leiostomus xanthurus),


pipefish (Syngnathus fuscus), bay anchovy  (Anchoa mitchilli), and silver


perch (Bairdiella chrysoura).  Collections are made by otter trawl over a


24 hour period.  From each sampling period, total gut contents of up to


six specimens are removed.  The contents and the fish are then dried and


weighed separately; the ratio of dry gut content weight to dry body weight


gives an analysis of feeding periodicity which, when combined with estimates


of evacuation rate at the temperature of collection, will allow analysis


of daily ration.  Analyses of samples taken in May and August are currently


underway.


     Preliminary experiments are being run in the laboratory to examine


the effect of artificial Zostera marina on predator-prey relationships of

migratory predators and resident fishes.  The experimental setup (Figure 4)


consists of two circular wading pools, (3.66 m in diameter, 0.9 meters


deep) with a volume of approximately 9500 liters each.  The present

design utilizes a closed system with a biological filter comprised of


0.24 m3  of coarse sand, oyster shell, and gravel; circulation is pro-


vided by two 38 liter per minute pumps.  Predators are captured by hook

                                                                  x
and line, prey fishes by cast net, otter trawl, and dipnet.  Predators are


maintained as residents in the tanks; holding tanks provide a supply of

-------
                                                                             99
Figure 4:  Present laboratory ta,nk setup for the preda,tor-
-------
Figure 4

-------
                                                                       100
both predator and prey fishes.  Artificial eelgrass (3/16" wide green




polypropylene ribbon, 0.6 density) mats have been woven to observed field




densities (dense- 1750 blades/m2; average— 875 blades/m2).  Mats (1 m2)




will be placed in the center of the experimental pools to mimic an




eelgrass habitat; prey will be released into the center of the tanks




in both eelgrass densities and in bare bottom controls.  Preliminary work




has involved setting up the experimental system, determining the proper




size of predators for the tank, determining appropriately sized prey for




the predators, and analyzing methodological problems as necessary for




determining final experimental design.




     Temperature acclimation tanks have been set up in the laboratory




with optional flow-through or closed system capabilities.  Current




acclimation temperatures are 12°, 17°, 22°, and 27°C.  This will allow




temperature related analysis of respiration rates and evacuation rates




of Bairdiella chrysoura, the silver perch, as part of a study on the




bioenergetics and physiology of this species.  Evacuation rate analysis




is also planned for the pipefish Syngnathus fuscus.  Respiration chambers




(Figure 5) have been constructed with flow-through characteristics to




allow analysis of metabolic rate at different temperatures.  Experiments




are currently being run with JB. chrysoura.

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                                                                           101
Figure 5:  Flow-through respirometer.  Although only two are shown, the system
           currently in use has five fish chambers (A), four of which contain
           fish and one of which is a control blank to monitor bacterial
           respiration.  Water is pumped through chambers and tubing by a.
           peristaltic pump (D) past oxygen probes (C) contained in special
           probe holders (B).  Flow rates are varied between 3 and 18 m/min
           depending on fish size and experimental temperature and are measured
           (E) during each experiment.

-------
Figure 5

-------
                                                                       102
                                RESULTS

Field Program

     Migratory predators sampled with  the gill nets are represented by

264 specimens of twelve species in nine families.  Data on catch for March

through August 1979 are presented in Table 1.  Catches (representing

number caught over the 24 hour period  with nets fished every four hours)

were very low in both March and April.  The April catch, represented by

a single bluefish (Pomatomus saltatrix) points up the variability in

catch of migratory predators.  One net in the sand area fished overnight

3 days prior to sampling (a set aborted by weather) caught 45 bluefish

as compared to 8 captured in the vegetated areas.  In May, catch increased

with movement into the bay of the teleosts Pomatomus saltatrix, Cvnoscion

nebulosus, JS. regalis, and the elasmobranchs Rhlnoptera bonasus and

DasyatIs say 1.  In June the sandbar shark, Ca_r_charhlnus milberti dominated

the catch and has continued as the dominant through July and August

(Table 1).

     The greatest catch of migratory predators was made in the Zostera

area (48%)  followed by Ruppia and sand areas (26% each).  The combined

catch In the vegetated areas (representing twice the fishing effort in

the sand area) provides preliminary evidence for the distribution of

the species relative to vegetation type.  The bluntnose stingray (Dasyatis

sayi) and the cownose ray (Rhinoptera  bonasus) are equally abundant in

sand and vegetated areas during months with low abundance; in May,

however, when the catch of the cownose ray was highest it occurred most
                                                                    v
frequently in the sand area.  The sandbar shark (C. milberti) was clearly

more abundant in vegetated areas.  Spotted seatrout (Cynoscion nebulosus)

-------
                                                                                            103
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                                                                      104
and weakfish (C. regalIs) were captured almost exclusively in vegetated

areas whereas bluefish (Pomatomus saltatrix) was dominant in the sand area

in two out of three months of collection.

     Two mesh sizes (12.7 and 17.8 cm square mesh) were used for migratory

predators; the larger mesh size was chosen to catch the sandbar shark

(Carcharinus milberti); only 12% of the catch of this species, however,

was made in the 17.8 cm mesh.  With the exception of Dasyatis sayi and

Rhinoptera bonasus, all species were captured to a much greater extent

in the 12.7 cin mesh.  These two species are probably sampled poorly in

gill nets; most catches occur through entanglement rather than via

"gilling" due to body shape.

     For most species there are insufficient captures to provide an adequate

estimate of diel temporal abundance patterns.  Diel pattern of catch for the

most abundant species (C. milberti) is presented in Figure 6 for June,

July, and August.  A cursory examination of the data suggests that the

highest rate of catch is in the late afternoon and dark hours.  The low

catch in the late afternoon of the second day in the June and August

collections, however, suggests this may not be the case; in all three months,

the first collection was made between 1200 and 1600.  In June, an additional

collection was made 24 hours after the first collection; the first collection

at 1500 resulted in a catch of 20 fish while none were caught at 1500 the

following day.   Similarly, the catch at 1630 was high the first day in the

August collection whereas only one individual was captured at 1500 the

following day.   This suggests that the population of £. milberti may be
                                                                    W
limited in this system and that 12 to 14 hours of fishing effectively removes

them; by comparison the catches of bluefish and Cynoscion do not appear

to show the same phenomenon.

-------
                                                                            105
Figure 6:  Temporal gill net catch of Carcharhinus milberti in all three
           sampling areas combined.  Nets are fished approximately each four
           hours over a 24 hour period each month; the points for the time
           of day represent the midpoint between setting and fishing the net.
           In all three months the first set was at approximately 1200 EDT.

-------
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      1200
          1600
2000
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1200
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                               TIME  OF DAY
                            Figure 6

-------
                                                                       106
     Resident fishes were sampled with the haul seine.  Data are considered

in this report from March through August 1979, which include 47 night and

9 day sets of the seine.  The resulting 4856 specimens represent 30 species

in 20 families.  Densities of the resident species taken in the monthly

night collections are presented Table 2.  Generally, numbers and diversity

of species were greatest in the Zostera area followed by the Ruppia and

sand areas.  The number of species captured and total fish density increase

with temperature through April and May.  Anchoa mitchilli was the most

frequently and consistently captured species; it was the numerical

dominant in the sand area in March and May and in all habitats during

the months of June through August. The Atlantic silverside, Menidia menidia,

was the dominant species in both vegetated areas in March, but decreased

in abundance in April and has been largely absent from night collections

since that time.  Spot, Leiostomus xanthurus, recruited to the Chesapeake

Bay in April and was clearly the numerically dominant species of resident

fish in all habitats.  Atlantic menhaden, Brevoortia tyrannus. has been

present in all months since April and was the dominant species in the

vegetated areas during May.

     Most species captured in the haul seine are relatively uncommon and

appear only sporadically.  Biomass (dry weight) of seven species is

presented in Table 3.  The dominant species in terms of biomass differs

from the numerical dominant in certain months; with few exceptions, however,

Anchoa mitchilli remains the dominant species.  In March, M. menidia is

dominant in all habitats; L,. xanthurus is the dominant species only in May
                                                                   t
in the Zostera sampling area.  Although clearly the numerical dominant in

April (Table 2), all specimens are newly recruited postlarvae (mean length

18.1 mm) which individually contribute little to the fish biomass.

-------
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-------
                                                                       109
     The day haul seine catches made in June included four species not




taken at night in any month; these were Gobiesox s trumosus,  (1),




Fundulus heteroclitus (1), Apeltes quadracus (3), and Pomatomus saltatrix




(1).  Biomass of the dominant species for day and night collections from




June is presented in Tahle A.  Brevoortia tyrannus is dominant in the




Zostera area during the day; all specimens, however, were taken in a




single collection and none were taken in the other two made in daylight




in Zostera.  By comparison this species was common at night only in the sand




area, where it was taken in all three collections.  It is possible that




these juveniles school in daylight and disperse at night.  Anchoa mitchilli




and Membras martinica occur in low densities (except for the latter species




in sand) during the day and are abundant during the night; for these two




species it is unlikely that the difference is an effect of enhanced




avoidance during the daylight samples, since Menidia menidia is captured




during the day.  The increased abundance of Syngnathus fuscus during the




day is probably due to increased activity during the day and better




availability to the sampling gear.  The lower daytime catches of Leiostomus




xanthurus in vegetated areas, however, probably represents increased




avoidance of the sampling gear; the ratios of night to day catch are




much greater in sand, however, suggesting that some movement from the




vegetated areas may occur at night for this species.




     Push net sampling has been conducted monthly at night with day




samples taken in May and August.  Sorting and identification of catch




for the ichthyoplankton samples (505 ym mesh) have been completed for




samples taken in March through July; this represents 38 total collections,




including 12 collections in the Ruppia area and 13 each in Zostera and

-------
                                                                          110
                                  TABLE  4

                               Resident Fishes
                         Day-Night Comparison (June)
                           Biomass (mg dry wt/m2)
                            Zostera              Ruppia             Sand
                           D	N	D    N	D	N

Brevoortia tyrannus      573.30       0           0   7.20          0  79.98
Anchoa mitchilli           3.64  176.95       12.70  95.23          0  80.73
Membras martinica          6.91   68.83        5.90  14.07      27.53   4.03
Menidia menidia           37.39       0        9.64      0       6.01      0
Syngnathus fuscus         15.82    8.19        1.08   0.58          0      0
Leiostomus xanthurus       6.33   54.59       16.82  43.87       0.87  17.18

-------
                                                                       Ill
sand habitats.  Volumetric and areal estimates of sampling effort

(Table 5) reveal moderate monthly variability but almost equal effort

(expressed as percent of total) between habitats.  Push net collections

yielded 2669 juvenile/adult fishes, 3243 larval/postlarval specimens

and 8235 fish eggs.

     Eggs of the windowpane flounder, Scopthalmus aquosus, the bay anchovy,

Anchoa mitchilli, and unidentified species of the family Sciaenidae

dominated push net collections (Tables 6 and 9).  Additional species

represented were Tautoga onitis, Trinectes maculatus, Membras martinica,

Hyporhamphus sp. and an unidentified goby species.  Eggs of the latter

three species are demersal, being attached to vegetation by chorionic

filaments (Atheriniformes) or laid in open shell nest sites (Gobiidae).

As a consequence, density estimates of eggs of these species cannot be

considered quantitative.

     Eggs of _A. mitchilli slightly outnumbered those of sciaenids

(1'63:1) and density estimates (May - July) were roughly comparable in

all habitats (Table 6).  During each month of occurrence, peak densities

of anchovy and sciaenid eggs were observed over the sand habitat and

lowest densities over Ruppia beds.  A^. mitchilli and sciaenid egg

abundance estimates ranged from 0.8 - 2018 eggs/100 m3 and 0.9 - 1159

eggs/100 m3 respectively.

     Larval and postlarval stages of 14 species representing 11 families

were taken in push net samples (Table 7).  In addition larval atherinids

(probably both Menidia menidia and Membras martinica) and Gobiosoma
                                                                    V
(probably both bosci and ginsburgi) were collected but reliable species

separation was not possible.

-------
                                                                 112
                         Table  5




Volumetric and areal estimates of sampling effort by pushnet




               at Vaucluse Shore study site.
Zostera
m3 m2
March
April
May (N)
(D)
June
July
Totals
% of Total
194.37
269.09
152.90
258.82
275.14
206.18
1,356.50
31.9
198.50
274.81
164.69
278.77
296.35
257.27
1,470.39
35.4
Ruppia
m3 m2
180.66
246.71
219.59
212.93
221.49
192.81
1,274.19
33.9
194.60
265.73
274.01
293.64
328.41
240.60
1,596.99
32.6
Sand
m3 m2
272.19
271.56
180.67
217.42
258.25
164.00
1,364.09
34.2
277.96
277.33
194.60
234.19
278.17
176.65
1,438.90
31.9

-------
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-------
                                                                       115
Ichthyoplankton collections were seasonally distinct.  The winter-spring

assemblage was dominated by postlarvae of Ammodytes hexapterus  and

Brevoortia tyrannus but also included postlarval Paralichthys dentatus

and larvae of JS. aquosus and Atherinidae species.  Premetamorphic (<  30 mm SL)

Ji. tyrannus peaked in density during April and appeared more abundant


over vegetated habitats.  In May, metamorphosed  (juvenile) specimens

(Table 8) exhibited a similar distributional patterns were apparent in

other winter-spring assemblage species.


     The  summer was characterized by greater diversity and

abundance and was dominated by larval anchovies, gobies,  and pipefishes

(Table 7).  Young Syngnathus fuscus and larval A_. mitchilli peaked in

abundance in July while the largest concentrations of Gobiosoma sp.

larvae appeared in June.  Larval anchovies and gobies were taken in


greatest  densities over non-vegetated habitat.  Collections of  young

pipefish  as well as the additional 7 species making up this summer


ichthyoplankton assemblage revealed no distributional patterns.

     Data on juvenile and adult fishes occurring in evening push net


samples are summarized in Table 8.  Four species appear to be consistently

available to the push net.  These include juvenile/adult  A^ mitchilli

and M. martinica and early juvenile stages of L_. xanthurus and  15. tyrannus.


The remaining species (as well as larger size classes of  B_. tyrannus  and

_L. xanthurus) are either effective avoiders of the gear,  occur  below

the sampling depth of the push net, or are infrequent in  the habitats


sampled.
                                                                  V.
     Day/night catch data (Table 9) for eggs and larvae was highly variable,


with no trends apparent.  As expected, however, catches of juvenile/adult


fishes were consistently highest during evening collections.

-------
                                                                     117
                         Table 91




Day versus night push net catch comparisons at Vaucluse  Shores.




                        31 May 1979
Species
Eggs (#/100 m3)
A. mitchilli
Sciaenidae
M. martinica
Unknown
Goniidae
Larvae (#/100 m2)
S. fuscus
C. re^alis
Gobiesox strumosus
Atherinidae
Gobiosoma sp.
A. mitchilli
H. hentizi
Juvenile (#/100 m2)
M. martinica
J5. tyrannus
A. mitchilli
L . xanthurus
S. fuscus
Hyporhamphus sp.
Zostera
Day Night
0.8
1.2
0.4
3.9
4.7
0.7
0.7
5.7
0.7
139.3
12.4
1.9
1.8
20.0
18.9
38.9
2.4
0.6
Ruppia Sand
Day Night Day Night
10.5 55.7 491.5
11.4 - 29.3
0.9 - 1.8
0.7 0.7 14.5 0.5
0.5
1.3
0.3 - 1.3
0.4
0.3
12.0 - 1.5
392.3 - 2.6
50.0 - 15.4
3.1
1.1 0.9
0.4

-------
116









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                                                                        118
     Zooplankton samples have been taken concurrently with ichthyoplankton

samples.  Most samples have been curated and analysis will begin in October

1979 in conjunction with the addition of personnel as requested in the amend-

ment to EPA.  In general the number of samples is double that for the

ichthyoplankton sampling with half used for biomass determination  and

half for taxonomic analysis.  Zooplankton biomass (mg ash-free dry weight/m3)

has been determined for March through July 1979 and is presented in Table

10 and Figure 7.  Biomass is determined as ash-free dry weight ("organic

weight") due to the occurrence of sand and particulate matter in these

shallow-water samples which are variable and often render dry weights

alone useless.  The trend shows that biomass is consistently greatest

in the Ruppia area, the shallowest area sampled; Zostera and sand areas

are approximately equal with fluctuations in certain months.  All values

are low in April and June.  April samples were taken after a storm which had

an effect on the fish populations; it may also have had an effect on the

zooplankton biomass.  It is possible, however, that the large populations

of postlarval spot  (Leiostomus xanthurus, see Table 2) may cause a reduction

through predation.  No explanation is apparent for the low values observed

in June.  Analysis of the taxonomic composition should help determine

certain of the causative mechanisms in the low values.  Day samples were

taken in May; the diurnal differences in biomass are apparent (Table 10).

The day samples, however, were taken after a storm had dropped approximately

two inches of rain on the area.  It is possible that the low biomass may be-

at least partially due to lowered salinity from the storm as well as
                                                                  t
vertical migration of components of the zooplankton.

-------
                                              119
     TABLE  .10

Zooplankton Biomass
   (rag AFDW/m3)
Nig






Day

ht Samples

March
April
May
June
July
Samples
May
Zostera

129
35
132
61
151

21

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225.
69.
397.
91.
380.

55.

3
3
5
7
6

7
Sand

234.2
39.8
118.6
32.1
164.5

51.2

-------
                                                                           120
Figure 7:  Organic biomass (Ash-free dry weight per m ) of zooplankton
           by habitat and month.  Each value represents the mean of two
           determinations.  R:  Ruppia area, Z:  Zostera area,  S:  sand area.

-------
a
u.
      400-1
      300 -
      200 -
      100
             MARCH
APRIL
MAY
JUNE
JULY
                           Figure 7

-------
                                                                      121
     Non-empty stomachs from 343 resident fishes representing 10 species


and 117 migratory predators representing 9 species have been collected,


sorted, and contents identified.  We are in the process of determining


dry weights of all contents and coding the data for computer analysis.


Additional specimens of these and other species have been taken to


complete size ranges and seasonal sampling of the resident fishes.


Stomachs from migratory predators continue to be taken as collected.


The species sampled, number of stomachs, and length range are presented


in Table 11.  Summer flounder (Paralichthys dentatus) has been treated


both as a resident fish and as a migratory predator.  Specimens under


200 mm SL are considered resident fishes; prey items are almost ex-


clusively invertebrates from within the eelgrass habitat, principally


mysids and Crangon septemspinosa.  Those specimens larger than 200 mm


prey almost exclusively on fishes, including Syngnathus fuscus and


Leiostomus xanthurus.


     Gravimetric analysis of the stomach contents and coding of the data


are currently underway.  Preliminary analysis of the feeding behavior of


three important members of the "true resident" group (based upon percent


frequency of occurrence of prey items) is presented in Figures 8-11.


Stomach contents of spot OL. xanthurus) collected in July 1978 and October


1978 are presented in Figures 8 and 9, respectively.  Fish collected in


July, when mean length was approximately 65 mm SL, fed predominantly upon


benthos as is apparent from the abundance of copepods (primarily harpacticoids),


nematodes, ostracods, polychaetes, and detritus (Figure 8).  Epibenthic

                                                                    u
and possibly planktonic feeding also occurred as shown by the presence


of amphipods, mysids, and fish eggs.  In October, when mean length of the

-------
                                                                            122
                                   TABLE ' 11

                                 Fish Stomachs
          Species                         Number               Length Range
Resident fishes
Urophysis regius
Syngnathus fuscus
Centropristis striata
Orthopristis chrysoptera
Bairdiella chrysoura
Leiostomus xanthurus
Prionotus carolinus
Paralichthys den tat us
Pseudopleuronectes americanus
Trinectes maculatus
8
84
3
16
111
87
11
14
8
1
41-120
61-160
61-160
21-120
41-140
61-160
21-120
121-200
41-100
121
Migratory predators

  Carcharhinus milberti                      56                  461-860
  Rhinoptera bonasus                          2                  741-946
  Pomatomus saltatrix                        32                  281-880
  Rachycentron canadum                        1                      410
  jjynps cion regal is                           6                  321-570
  _C. nebulosus                               11                  381-590
  Micropogpn undulatus                        1                      350
  S_ciaenops ocellata                          2                  381-780
  Paralichthys dentatus                       6                  241-440

-------
                                                                           123
Figure 8:  Percent frequency of occurrence of specific prey items in
           stomachs of resident fishes from the Vaucluse Shores study site.
           Numbers in the figures may not equal those in Table 11 due either
           to inclusion of empty stomachs (in the figures) or due to sub-
           sampling of available stomachs; Spot, Leiostomus xanthurus collected
           in July, 1978.

-------
lOOr
 75 -
        65.6
PERCENT FREQUENCY OF OCCURRENCE
? K 8


59,4

50.0

48-4

40-6

39-1

35,9

N=64
297

20.3
15.6 15.6 . , .
' 14.1
9.4
3.1

                              Figure  8

-------
                                                                      124
spot collected was 101 mm SL, mysid shrimp were more conspicuous in the

diet, but benthic feeding remained important (Figure 9).

     Feeding by the silver perch OB. chrysoura), all collected in the

month of October, is notably different from that of spot (Figure 10).

Harpacticoid copepods, nematodes, and other evidence of benthic feeding

is lacking.  Mysids are clearly the dominant food item, as both numerical

and preliminary gravimetric analyses confirm.  Planktivorous feeding

is taking place as demonstrated by presence of mysids and calanoid

copepods.  Feeding within the vegetated areas is suggested by the

abundance of amphipods and other epifauna.  Pipefish (Syngnathus fuscus),

captured almost exclusively in vegetated areas (Table 2), feeds on a combination

of prey items from within and outside of the vegetated areas (Figure 11).

Calanoid copepods occur most frequently in the fish collected in July,

along with Caprella penantis and other amphipods.  In the October

collections, however, mysids (Neomysis americana) clearly dominate the

diet; calanoids remain relatively important in the diet, but amphipods

are consumed less frequently (Figure 11).

     The migratory predators feed primarily on fishes and blue crab,

Callinectes sapidus.  Spotted seatrout (Cynoscion nebulosus) and weakfish

(C. regalis) show similar feeding habits.  Both species have been caught

mostly in the vegetated areas (Table 1).  Diet is comprised primarily of fishes

(Including small Brevoortia tyrannus and Leiostomus xanthurus) with lower

frequencies of invertebrates (Crangon septemspinosa, Palaemonetes vulgar!s

and a single small Callinectes japidus).  The sizes of fish preyed upon
                                                                     \,
suggest that they are captured within the vegetated areas where the fish

-------
                                                                           125
Figure 9:  Percent frequency of occurrence of specific prey items in stomachs
           of resident fishes from the Vaucluse Shores study site.  Numbers
           in the figures may not equal those in Table 11 due either to
           inclusion of empty stomachs (in the figures) or due to sub-sampling
           of available stomachs; Spot, Leiostomus xanthurus, collected in
           October 1978.

-------
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-------
                                                                           126
Figure 10:  Percent frequency of occurrence of specific prey items in stomachs
            of resident fishes from the Vaucluse Shores study site.  Numbers
            in the figures may not equal those in Table 11 due either to
            inclusion of empty stomachs (in the figures) or due to sub-
            sampling of available stomachs; Silver perch, Bairdiella
            chrysoura, collected in October 1978.

-------
   100-r
    75f
u
U
ff
K
D
u

8
u
z
u
3
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oc
           82.3
                                          N=I3O
               274
                                  Figure 10

-------
                                                                           127
Figure 11:  Percent frequency of occurrenct of specific prey items in stomachs
            of resident fishes from the Vaucluse Shores study site.  Numbers
            in the figures may not equal those in Table 11 due either to
            inclusion of empty stomachs (in the figures) or due to sub-
            sampling of available stomachs; Pipefish, Syngnathus fuscus
            collected in July 1978(left) and October 1978 (right).

-------
oo
•r-l
                              30N38UnOOO dO AON3riO3Hd iN3DH3d

-------
                                                                       128
were caught.  The dominant migratory predator after the May collections

was the sandbar shark (Carcharhinus milberti) for which the dominant food

items have clearly been fish and blue crab.  Based upon frequency of

occurrence, 54% have contained both fish and crab, 15% exclusively crab,

and 31% exclusively fish.  Of those fish which were identifiable,

Brevoortia tyrannus, Leiostomus xanthurus, and Hypsoblennius hentzi were

represented; all of these species are probably taken in the vegetated

areas.  For those stomachs where dry weight of contents has been

determined, fish represents, on the average, 2.1 times the weight of

crab consumed.  The final species of migratory predator, Pomatomus saltatrix,

feeds almost exclusively on fish with a single occurrence of blue crab.

The dominant prey species have been spot (25% of identifiable fish

occurrences) and menhaden (58%); in contrast to the sandbar shark and

Cynoscion spp., however, the menhaden consumed by bluefish are generally

larger and probably are captured outside the vegetated area.

     One species included in the resident fishes is the spotted hake,

Urophysis regius.  This species was captured in a single trawl taken in

May during a sampling effort aborted due to weather; it has not been taken

prior to this time or in a series of trawls made the following week.  Eight

specimens have been examined for stomach contents, all of which had

consumed fish.  The only identifiable fish species was spot, Leiostomus

xanthurus.  From this consideration this species, although small (41-120 mm SL)

might be defined as a migratory predator.

     Adequate predators for the predator-prey laboratory experiments have
                                                                   v
been determined.  Summer flounder (Paralichthys dentatus)„ bluefish

(Pomatomus saltatrix), and weakfish (Cynoscion regalis) have been success-

fully maintained in both holding and experimental tanks.  The size range

-------
                                                                       129
best suited to the size of experimental tanks is from 250 to 350 mm




standard length.  Summer flounder and bluefish generally commence




feeding on live food after one week or less in captivity, whereas weakfish




would not feed for a minimum of three weeks.  All three of these species




are taken in the vegetated areas at the study site; feeding behavior indicated




that fish is the primary food.




     Five species have been assessed as potential prey for the experiments.




The mummichog (Fundulus heteroclitus) showed excessive orientation to the




sides of the tanks; its availability, however, is such that it may be used




for feeding predators between experiments.  The pipefish (Syngnathus fuscus),




although important in vegetated areas and showing proper behavior to




artificial eelgrass, orients to the bottom and walls of the experimental tank




such that predation is nil or low even in the unvegetated controls.  The




three species chosen for the experiments are spot (Leiostomus xanthurus),




silver perch (Bairdiella chrysoura), and menhaden (Brevoortia tyrannus).




All are important species in the vegetated areas of the study site in




the diets of the three predator species.  Spot remain motionless in the




bottom of the tank in unvegetated controls, showing movement when con-




fronted by a predator species.  Bairdiella, by contrast, generally remains




in midwater.  Menhaden show schooling behavior, especially when pursued




by a predator.   The size ranges of all prey species are from 40 to 80 mm SL.




     The predators behave differently with respect of prey pursuit.  Bluefish




approach the prey directly and usually slash or bite the prey to pieces, as




described in Olla et al (1970).  Weakfish show a more cautious pursuit




and attack usually from below.  Flounder stalk prey and usually approach




from behind.  The behavior of predators and preliminary experiments suggest




that the predators will have varying success in the presence of artificial




eelgrass.

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                                                                      130
                               DISCUSSION

     Although an entire sampling season has not been completed, the trends


in distribution and abundance of the migratory predators and resident


fishes recorded in the present study generally show agreement with other


studies in shallow-water habitats in the lower Chesapeake Bay (Orth and


Heck, in press).  The migratory predators (Table 1) show sporadic occurrences


with the exception of the sandbar shark, C. milberti, which was consistently


abundant during the last three months addressed in the present report.


Although gill nets are selective (Hamley 1975), the catch in this study

appears to give an estimate of relative abundance of most species with


the probable exception of the rays Rhinoptera bonasus and Dasyatis sayi


and probably the summer flounder Paralichthys dentatus.  The rays are


dorso-ventrally flattened and are captured largely due to entanglement.


Although the nets foul visibly with jellyfish, large ctenophores, and


drifting aquatic vegetation due to current flow, the catch is not


markedly greater at night when visual detection would be less effective;


this may be due to the low water clarity during most months.  The temporal

catch of Q. milberti shows increases at night but temporal catch is


difficult to analyze due to removal of an apparently resident population

without replacement (Figure 6).  Combining catch of both species of


Cynoscion from May through September, 43% are captured during daylight


hours, whereas  63% of bluefish (jP. saltatrix) were caotured in daylight


hours.  This contrasts with the data of Pristas and Trent (1977), who found


93% of the twelve most abundant species taken at night in gill nets.  Thus
                                                                    v

movement to the shallow water areas is probably greatest during daylight


hours when active feeding takes place.

-------
                                                                      131
     Availability of most species arises from populations moving through

the area or coming from adjacent deeper water areas.  This is apparently

not true for the sandbar shark (C. milberti), which appears to exist in

essentially resident populations which are removed within 12-14 hours after

initial setting of the gill nets (Figure 6); status as a "resident"

predator is consistent with the fact that it was captured primarily in

the vegetated areas with slightly greater abundance in the Zostera area

(Table 1).  Although captured most frequently in the vegetated areas as

well, the spotted seatrout and weakfish (Cynpscion nebulosus and £. regalis)

do not show a pattern of catch indicative of residence in the bed; bluefish

(£• saltatrix), on the other hand, exhibits a greater variability in catch

from month to month but in general is most frequently captured in the

sand area.  The feeding habits of these migratory predators reflect the

habitat of occurrence.

     Resident fishes sampled by the haul seine show the seasonal trends

observed for collections made two years earlier using a trawl at the same

study site (Orth and Heck, in press).  In the current study, the

immigration of spot (_L. xanthurus) to the seagrass bed did not occur

until mid to late April (Table 2), later than observed in 1977 (Orth and

Heck, in press) in lower Chesapeake Bay or for most years in vegetated

areas south of Cape Hatteras (Adams 1976a; Thayer et al 1974).  The

numerically dominant species observed by Orth and Heck was spot, whereas

the numerical dominant in the current study is the bay anchovy (A. mitchilli)

The increased importance of the pelagic species (B. tyrannus, A^. mitchilli,
                                                                     t.
M- nienidia, and M. martinica) in the current study is probably due to the

difference in gear type.  Orth and Heck used a 16 foot otter trawl towed

-------
                                                                      132
behind an outboard vessel which fishes effectively only one meter off the

bottom; thus both avoidance and fishing of the net below the depth of

occurrence of these species suggests that their relative abundance was

underestimated.  Adams (1976a) showed dominance of pinfish (Lagodon

rhomboides) and pigfish (Orthopristis chrysoptera) in North Carolina

eelgrass beds; the former, although present in low abundance in the study

by Orth and Heck, was not captured in the current study, and the latter

was present only in low numbers (Table 2).  Spot, however, occurred

later in the year in densities similar to those observed by Adams (1976a)

using a dropnet.

     Within the resident fishes, two subgroups are apparent.  The first

is comprised of the pelagic and/or schooling group ("pelagic residents")

including Ji. tyrannus, _A. mitchilli, M. martinica, and M. menidia.  Adams

(1976a) did not consider these species as true residents of the bed.

Although the same is probably true in the present study for all four

of the above species, they are considered with the residents in terms

of ecological impact upon the ecosystem due to the relatively high

biomass in the vegetated areas.  In the night collections these species

were taken in all three habitats (Table 2) without clear trends in

abundance.  Comparing day and night collections for June (Table 4),

no trend is apparent for JJ. tyrannus due to its highly contagious

distribution; A. mitchilli is present in vegetated areas in the day,

increasing greatly in these areas and in the sand area at night.  M.

martinica is taken in low abundance during the day except in the sand
                                                                  V
area; the situation reversed during the night.  The other atherinid,

M. menidia, however, shows an opposite pattern; none were captured at

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                                                                       133
night except in March and April while Membras densities were low.  In




the day collections, however, Menidia was common, especially in Zostera.




     The second group of resident fishes  ("true residents") is dominated




by spot  (L. xanthurus) and pipefish (S^. fuscus) and includes the




majority of other species included in Table 2.  In August, silver perch




(_B. chrysoura) appeared and has remained important in subsequent months




as observed by Orth and Heck  (in press); the other sciaenids (C. nebulosus,




JC. regal is, M. ajnericanus) captured in August did not remain as important




components of the community.  Members of this component of the resident




fish group are captured most  frequently in the vegetated areas with




greater catches in the Zostera sampling area (Table 2).  Day-night




sampling conducted in June suggests that S_. fuscus is more abundant in the




day, but this probably reflects greater availability to the haul seine.




Spot, on the other hand, appear more abundant in the night collections.




Orth and Heck (in press) observed increased catch of spot in all habitats




at night as observed in the present study.  It remains to be determined, however,




whether the increases at night are due to increased daytime avoidance or




to actual movements to the bed from other areas.  The relative increases




are greater in unvegetated areas, however, suggesting that some movement




may occur between vegetated and unvegetated areas, as suggested by Orth




and Heck.  In general, the biotnass reported in the present study




for the seven major species falls within the range of total fish biomass




for Zostera marina beds in New England by Nixon and Oviatt (1972) but




is less than that reported in studies to the south (North Carolina, Adams 1976a;




Texas, Hoese and Jones 1963).




     Ichthyoplankton collections from shallow-water vegetated habitats




have not been analyzed in the lower Chesapeake Bay; qualitative comparisons,

-------
                                                                     134
however, of the present Ichthyoplankton data with those of previous

studies on Chesapeake Bay fish eggs and larvae (Pearson 1941, Dovel

1971, Olney 1978) indicate that the push net presently employed as

primary ichthyoplankton gear in this study adequately samples nearshore

ichthyoplankton assemblages.  Species composition and seasonality of

Vaucluse Shores ichthyoplankton (March-July) are in general agreement

with all previous Chesapeake Bay studies.  Without exception, all

species encountered in the present collections have been previously

recorded as eggs, larvae or juveniles in similar seasonal patterns.

     Although quantitative comparisons are limited by natural variability,

difference in methodology, and lack of comparative gear efficiency data,

relative ichthyoplankton abundance as measured in the present study

compares favorably with the most recent data on lower Bay fish eggs and

larvae (Olney 1978).  Differences noted may be instructive in pointing

out the importance of nearshore spawning nursery habitats.  Present ranges

of density estimates (///100 m ) for eggs of A. mitchilli and sciaenid

fishes (0.5 - 2018.3 and 0.9 - 1159.2 respectively) are comparable to

those reported by Olney (3200-14000 A. mitchilli eggs; 6.0 - 819

sciaenid eggs).  Both studies found eggs of Anchoa and sciaenid fishes

to dominate fish egg collections, but differences in absolute ratios of

Anchoa to sciaenid eggs (1.63:1, present study; 15:1 Olney's data)

suggest reduced Anchoa nearshore spawning activity and greater utilization

of nearshore spawning habitat by sciaenids.  Similarity, differences in

abundances of goby and pipefish larvae relative to larval Anchoa point
                                                                    v
out increased utilization of shoal, vegetated habitats as spawning grounds

for these species.  In the present data, pipefish and goby larvae occurred

-------
                                                                      135
in equal and sometimes greater concentrations than anchovies.  In contrast,

larval concentrations of these species never surpass those of Anchoa in

deeper waters (Olney 1978).

     Continued examination of nearshore ichthyoplankton assemblages

utilizing this gear will be instructive.  In future reports, we will include

length-frequency analysis, additional day-night comparisons, data on the

relationship of hydrographic parameters to species occurrence, and comparative

gear evaluation.

     Variation between habitats for components of the ichthyoplankton

differ between stages (Tables 6-8).  Eggs of Scopthalmus aquosus are about

equally distributed between the three habitats during the months of March

and April.  The more abundant eggs of Anchoa mitchilli and of sciaenids

show virtually the same pattern (lowest densities in the Ruppia area,

increasing in the Zostera area, and highest in the sand area).  Since

much of the water flow to the bed occurs up the main channel during

flood tide (Figure .1), this is consistent with spawning activity either

in deeper water, which communicate directly with the sand area, or

possibly in the main channel or upstream in Hungar's Creek.  The

great density of both egg types in the sand area in July, however, favors

the former explanation (Table 6).   Very small larvae (Table 7) show

either no difference between habitats or show a pattern similar to

that of the eggs of Anchoa.   With growth, however, postlarvae of some

species show increased densities in the vegetated areas (Table 7).  15.

tyrannus and 1^. xanthurus, for example, are spawned off the Atlantic
                                                                  t
shelf and move into the Chesapeake Bay, arriving as postlarvae in the

-------
                                                                      136
shallow water habitats.  Recruits of both IJ. tyrannus (Table 7)




and L. xanthurus (Tables 2 and 8) appear to prefer vegetated habitats.




     The temporal pattern of variation in zooplankton biomass is similar




to that observed in a study of the plankton of the lower Chesapeake Bay




(Jacobs 1978).  Values observed in the sand and Zostera areas fall within




the ranges observed by Jacobs, but the values for the Ruppia area greatly




exceed those observed in open bay waters.  The low values observed in




the month of April coincide with the recruitment of large numbers of




postlarval spot (L. xanthurus) and menhaden (B. tyrannus) to the lower




Bay (Tables 2 and 7).  These species are planktivorous in the postlarval




stage; it has been suggested that immigration of large numbers of




postlarval fishes may significantly reduce the standing crop of zooplankton




in estuarine systems (Thayer et al 1974).  In sampling deeper water,




however, Jacobs (1978), although noting a decrease in zooplankton biomass




in April, did not demonstrate a significant reduction in copepod density;




a reduction would be expected if postlarval feeding was the causative




factor since copepods make up 76-99^ of the food of these fishes in this




stage of the life history (Kjelson et al 1974).  The diurnal differences




in zooplankton biomass (Table 10) for May demonstrate a dramatic reduction




in the day samples.  Although Ruppia remains the highest value, the day




value in vegetated areas is 15% that of the night value as compared to




43% in the sand area.  Further analysis of the curated samples will




elucidate the meaning of the temporal changes in zooplankton biomass.




     Organic biomass of zooplankton collections shows clear differences




between habitats (Table 10, Figure 7).  Generally, biomass is greatest in




Ruppia followed by sand and Zostera with the latter two showing similar

-------
                                                                       137
values.  Although the Importance of these differences must await analysis


of the taxonomic composition of the plankton, three hypotheses are


consistent with this observation, as follows:  1) obligate planktonic


organisms collect in high densities in the upper end of the channel


through hydrodynamic winnowing, active orientation, or swarming behavior;


2) facultative or demersal plankton are more abundant in the shallower


water of the Ruppia zone; or 3) organic detritus and particulate matter


retained by the 202 ym mesh is more common in the Ruppia area.  Evidence


against hydrodynamic winnowing is provided by the abundance pattern of


fish eggs (Table 6) as discussed above, which are in lowest densities in


the Ruppia area (unless high planktonic predation rates on egg stages


lowers density).  Swarming behavior has been observed in several shallow water


habitats, including coral reefs, marine lakes, seagrass beds, and rock


and sand bottoms by a variety of obligate planktonic taxa including copepods,


euphausids, and mysids (Emery 1968; Fenwick 1978; Hamner and Carleton


1979).  The samples in the Ruppia area are generally taken at peak high


tide (before ebb) to provide the water depth necessary for the push net.


Swarming would probably be facilitated during times of slack water.  The


contribution of obligate or facultative plankton or of organic detritus

to the high values of zooplankton biomass in the Ruppia area must await


analysis of the taxonomic composition of the curated samples.


     Feeding relationships of fishes within the Vaucluse Shores study site


are generally similar to those of the dominant speices observed in other


studies in vegetated habitats (Carr and Adams 1973; Adams 1976c).   The
                                                                   *.

lack of the dominant species from North Carolina  (Lagodon rhomboides and


Orthopristis chrysoptera) , however, may alter the feeding behavior of

-------
                                                                       138
L. xanthurus in the current study through availability of other food sources.

Although plant material and detritus occur frequently (Figures 9 and 10),

preliminary gravimetric data suggest that they are less important in the

diet than in North Carolina Zostera beds (Adams 1976c) or in Florida

(Sheridan 1978).  The frequency of occurrence reflects the frequency of

benthic feeding rather than dietary importance.  Spot are initially

planktivorous, after which they switch to predominantly benthic feeding

(Kjelson et al. 1974; Sheridan 1978); this will be confirmed in the current

study in conduction with zooplankton sampling in the spring of 1980.

Smaller (average 65 mm SL, July data)  spot exhibit predominantly benthic

feeding (Figure 8).  Although benthic feeding remains important in larger

specimens collected in October (Figure 10), planktonic feeding represents

the major food intake; analysis shows that numbers of harpacticoids and

nematodes decline rapidly with size whereas the numbers of raysids per

stomach increases.  The data is confounded, however, by the sampling

of smaller fish in July, when mysids were rare in the eelgrass bed, and

larger fish in October, when mysids were abundant (see part II of this

report).  The increases in importance of mysids in the diet are likely

evidence of high availability, since I,, xanthurus has a subterminal mouth

adapted primarily to feeding on infauin and benthic organisms (Chao and

Musick 1976).

     Bairdiella chrysoura immigrates to the vegetated areas in August

(Table 2).  Stomachs have been analyzed from collections in October 1978,

when the fish were relatively large (mean length approximately 92 mm SL;
                                                                   t
see Table 11).   This species has a terminal mouth and is adapted for pelagic

feeding, although some epibenthic feeding takes place (Figure 10).  Most

-------
                                                                       139
studies on the feeding by this species (summarized in Chao and Musick




1976) show fish, mysids, and decapod shrimp to be the predominant dietary




items.  Adams (1976c), by contrast, observed no mysids in the diet of




this species in North Carolina eelgrass beds.  The abundance of mysids




in the diet is undoubtedly related to the high levels of abundance in




the eelgrass habitat.  The importance of availability upon feeding on




mysids within the bed is stressed by the change in frequency of mysids




in stomachs of pipefish (S_. fuscus).  Mysids were not present in stomachs




of specimens taken in July but represented the major food item in October




(Figure 11).  The ongoing gravimetric analysis of prey items will provide




more precise definition of ontogenetic and seasonal trends of feeding




behavior of the fish community, their relationship to prey availability,




and the impact on other components of the ecosystem.

-------
                                                                        140
                             LITERATURE CITED






 Adams, S. M.  1976a. The ecology of eelgrass, Zostera marina  (L.)> fish




      communities.  I. Structural analysis.  J. exp. mar. Biol. Ecol.




      22:269-291.




 Adams, S. M.  1976b. The ecology of eelgrass, Zostera marina  (L.), fish




      communities.  II. Functional analysis.  J. exp. mar. Biol. Ecol.




      22:293-311.




 Adams, S. M.  1976c. Feeding ecology of eelgrass fish communities.




      Trans. Amer. Fish. Soc.  105:514-519.




 Briggs, P. T., and J. S. O'Connor.  1971.  Comparison of shore-zone fishes




      over naturally vegetated and sand-filled bottoms in Great South




      Bay.  N.Y. Fish Game J.  18:15-41.




 Carr, W. E. S., and C. A. Adams.  1972.  Food habits of juvenile marine




      fishes:  Evidence of the cleaning habit in the leather jacket




      Oligoplites jjaurus, and the spottail pinfish Diplodus holbrpoki.




      Fish. Bull.  70:1111-1120.




 Carr, W. E. S., and C. A. Adams.  1973.  Food habits of juvenile marine




      fishes occupying seagrass beds in the estuarine zone near Crystal




*     River, Florida.  Trans. Am. Fish. Soc.  102:511-540.




 Dovel, W.  1971.  Fish eggs and larvae of the upper Chesapeake Bay.




      Nat. Res. Inst., Univ. of Md.  Contrib. #460, 71 pp.




 Emery, A. R.  1968.  Preliminary observations on coral reef plankton.




      Limn. Oceanog.  13(2):293-303.




 Fenwick, G.  1978.  Plankton swarms and their predators at the Snarves




      Islands.  N.Z. Journal Mar. Freshwater Res.  12:223-224.




*Chao, L. N., and J. A. Musick.  1976.  Life history, feeding habits, and




      functional morphology of juvenile sciaenid fishes in the York River




      estuary, Virginia, Fish. Bull. U.S.  75:657-702.

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                                                                      141
Hamley, J. M.  1975.  Review of gill net selectivity.  J. Fish. Res.




     Bd. Can.  32(11):1943-1969.




Hamner, W. H., and J. H. Carleton.  1979.  Copepod swarms:  attributes




     and role in coral reef ecosystems.  Limnol. Oceanogr.  24:1-14.




Hoese, H. D., and R. S. Jones.  1963.  Seasonality of larger animals in




     a   Texas grass community.  Publs. Inst. mar. Sci. Univ. of Texas.




     9:37-46.




Jacobs, F.  1978.  Zooplankton distribution, biomass, biochemical composition,




     and seasonal community structure in lower Chesapeake Bay.  Ph.D.




     Dissertation, University of Virginia.  Charlottesville, Va. 105 pp.




Kjelson, M. A., D. S. Peters, G. W. Thayer, and G. N. Johnson.  1974.




     The general feeding ecology of postlarval fishes in the Newport




     River Estuary.   Fish. Bull.  73:137-144.




Kjelson, M. A. and G. N. Johnson.  1974.  Description and evaluation of a




     long haul seine for sampling fish populations in offshore estuarine




     habitats.  Proc. 28th Ann. Conf. S. E. Assoc. Game Fish Conm.




     pp. 171-175.




Moseley, F. N. and B. J. Copeland.  1969.  A portable drop-net for




     representative sampling of nekton.  Contr. Mar. Sci. Tex.  14:37-45.




Nixon, S. W. and C.  A.  Oviatt.  1972.  Preliminary measurements of




     mid-summer metabolism in beds of eelgrass, Zostera marina.  Ecology.




     53:150-153.




Olla, B. L., H. M. Katz, and A. L. Studholme.  1970.  Prey capture and




     feeding motivation in the bluefish, Pomatomus saltatrix.  Copeia.




     14:360-362.

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                                                                      142
Olney, J. E.  1978.  Planktonic fish eggs and larvae of the lower Chesapeake




     Bay.  MS Thesis, College of William and Mary, Williamsburg,




     Virginia.  123 pp.




Orth, R. J.  1975.  Destruction of eelgrass, Zostera marina, by the




     cownose ray, Rhinoptera bonasus, in the Chesapeake Bay.  Ches.




     Sci.  16:206-208.




Orth, R. J., and K. L. Heck, Jr.  In Press.  Structural components of




     eelgrass (Zostera marina) meadows in the lower Chesapeake Bay:




     fishes.  Estuaries.




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     Chesapeake Bay, Virginia, with special reference to the grey sea




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Pristas, P. J., and L. Trent.  1977.  Comparisons of catches of fishes




     in gill nets in relation to webbing material, time of day, and




     water depth in St. Andrew Bay, Florida.  Fish. Bull.  75:103-108.




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     fishes, in the vicinity of Cedar Key, Florida.  Bull. mar. Sci.




     Gulf. Caribb.  4:1-94.




Sheridan, P. F.   1978.  Trophic relationships of dominant fishes in the




     Apalachicola Bay system (Florida).  Ph.D. Thesis, Florida State




     Univ.  232 pp.




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     of zooplankton in the Newport River estuary.   Ches. Sci.  15:9-16.

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                             ECOSYSTEM MODELING




                                R. L. Wetzel




                               INTRODUCTION






     The ecosystem modeling project is designed and being implemented as




an integrative tool for ecosystem analysis.  The modeling effort will




describe the principal pathways for energy flow and evaluate those parameters




associated with specific processes that control behavior.  The tasks  to




date  have centered on model conceptualization, parameterization and




mathematical formulation for digital computer simulation.






                                   METHODS




Conceptualization;  Model conceptualization or compartmentalization is based




on trophic interactions.  The information used to decide the compartmental




structure for the model came primarily from the literature and relied




heavily on the expertise and experience of the several principal investiga-




tors participating in the overall research program.  Following two prelimi-




nary versions, the model proposed for simulation was decided.  Table 1




lists and describes the 1? compartments of the model and Figure 1 gives




the interaction matrix describing compartmental exchanges.  Emphasis in




this model version is placed on biological organization and trophic function




in response to the overall program objective to evaluate predator-prey




interactions and secondary production.  Evaluation of controls such as




temperature, light and nutrients on primary production within the context




of the model will be studied in a second model version following preliminary




analysis using the current model structure.

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                                                                           145
Table 1:  Model compartmentalization
Symbol              Name

XI                 C02-H20

X2                 POC-H20

X3                 DOC-H20

X4                 POC'Sed

X5                 DOC'Sed

X6                 Phytoplkankton

X7                 Vascular Plants

X8                 Epiphytes


X9                 Benthic Algae


X10       Zooplk. & Meroplankton



XI1       Microheterotrophs'H 0

XI2       Attached Epifauna


XI3       Motile Epifauna


X14       Heterotrophs-Sed

X15       Microheterotrophs-Sed

X16       Natant residents

XI7       Megapredators &
           Waterfowl
Description

Carbon dioxide J.n water

Particulate organic carbon  in water

Dissolved, organic carbon  in water

Particulate organic carbon  in, sediments

Dissolved organic carbon  in sediments

All autotrophic water column components

Zostera marina, Ruppia maritima

Autotrophes associated with emergent
vascular plant leaves

Both macrophytic and microautotrophs assoc.
with sediments.

Heterotrophs in water column.   Includes both
resident and seasonally abundant larval and
juvenile forms.

Primarily bacteria in water

Sessile heterotrophs associated with emergent
vascular plant parts

Heterotrophs that are capable of free movement
within the vascular plant community.

Primarily infauna

Primarily bacteria in sediments

Large predatory, motile species

Self-explanatory

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                                                                         146
Parameterization;  The parameters necessary as input data for model simula-

tion can be grouped according to equation structure.  The equational structure

is based on the type of exchange in question.  Generally these fall in one

of four categories:  1. abiotic-*-abiotic, 2. abiotic Abiotic, 3. biotic ->•

biotic and 4. biotic-> abiotic exchanges.  Because of the high degree of

biological interaction represented in the current model version, parameters

associated with the last two categories of exchange dominate the data

input requirements.  The following summary defines these parameters and

together with the next section on mathematical structure forms the basis

for the computer simulation version of the model.  Briefly the parameters

currently being evaluated;

Given two generalized compartments and represented as:

                              Fij
where;  Xi = donor compartment "i"
        Xj = recipient compartment "j"
        Fij = flux of matter-energy from "i" to "j"

the parameters necessary to describe the various flows in the model are:

1.  Pi j ; a dimensionless number where
that gives the preference assigned an ingestion or uptake pathway, Fij.

For any biotic compartment having multiple resources  (2 or greater) , a

preference value in the above range must be decided such that,
              n
              £pij=1.0, n= number of inputs to Xj
                i=l

This applies, in its present form, to only biological uptake pathways.
                                                                     V
2.  Ti j :  The maximum specific rate of uptake or ingestion as;

                gC(Xi) . gC(Xj)-1  . At'1

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                   Figure 1:  Model Interaction Matrix
144
From; 1
I. C02.H20
2. POC.H20
3. DOC.H20
4. POC.Sed.
5. DOC.Sed.
6. Phytoplk. D
7. Vas. Plants D
8. Epiphytes D
9. Benthic D
Algae
0. Zooplk & D
Meroplk
1. Microhetero D
2 . Attached D
Epi fauna
3. Motile D
Epi fauna
4. Hetero.Sed. D
5. Microhetero
Sed.
6 . Natant
Residents
7. Megapred.
Waterfowl
2



RS

M
M
M

M/Eg

M/Eg



M/Eg
M£g
3




Ex
EC
EC
EC

EC
EC
EC



EC
EC
4

S




M

M



M/Eg
M/Eg

M/Eg

5


Ex



EC

EC



EC
EC
EC
EC

6
R
















7
R
















8
R
















9
R
















10





DR

DR


DR






11

DR
DR














12





DR



DR
DR






13






DR
DR
DR


DR

DR
DR


14






DR

DR





DR


15



DR
DR












16








DR
DR
DR
DR
DR
DR
DR


17






DR





DR
DR

DR

                                                                              4

                                                                              2

                                                                              2

                                                                              2

                                                                              2

                                                                              5

                                                                              8

                                                                              5

                                                                              6
                                                                             6

                                                                             5
                                                                            _3
                                                                            76
D = Linear Donor controlled (LDC)
RS = Resuspension - LDC
M = Mortality - LDC
Eg = Egestion - LDC
EC * Excretion - LDC
S = Sedimentation
DR = Donor-Recipient Controlled

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                                                                         147





where,



                  Xi and Xj as above



                  gC = grams of carbon



                 At = time interval



For the current model version carbon is the unit of exchange and the unit



of time equals one day.  For our preliminary simulation work with the model,



four  (4) seasonal values are assigned each ingestion or uptake pathway, i.e.



winter, spring, summer and fall values.



3.  AEi j :  The assimilation efficiency for the corresponding ingestion or



uptake pathway, Fij where,



                  0
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                                                                          148
 maximum maintainable density for the recipient population.   This is equivalent

 to the "carrying capacity" or K-value from other works.   Units as above.
                                 n
                   At, Xj =y jj,  EFij = maintenance costs of Xj
                                i-1

                                   n = no.  input pathways

                   and A xj.At"1=0.    no growth

 The above seven parameters in equational form define the principal biological

 interactions for uptake or ingestion of matter-energy.   The following describe

 the losses of matter-energy from the various populations.

 8. Pj ; Specific rate of respiration as gC.gC~l. t~l.

 9. Cj : Specific rate of excretion as gC.gC'l. t~*.

10. yj ;  Specific rate of natural mortality exclusive of predatory mortality

 as gC.gC"1. t"1.


 Mathematical Structure

      The mathematical structure of the simulation model and formulation of

 interaction equations follows the general guides presented by Wiegert

 (1975, 1978).  The interaction equations coupling the compartments (Table 1)

 are based on testable assumptions and incorporate measurable parameters;

 i.e.  the interaction coefficients are dimensioned and have ecological meaning.

 The technique used for digital computer solution of the simulation model

 follows Wiegert and Wetzel (1974).

      The current model version has 76 pathways for exchange.  The equations

 used to describe these can be mathematically classed into one of three

 general categories:
                                                                      v
      1. linear, donor controlled pathways

      2.  linear, recipient controlled pathways

      3.  non-linear, recipient controlled, donor-recipient determined pathways
          (feedback controlled)

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                                                                         149
Of the 76 pathways the majority  (34) are classed as category three, i.e.

feedback controlled ingestion or uptake fluxes.  Thirty  (30) pathways represent

metabolic loss or natural mortality for the biotic compartments and are

classed as category 1, i.e. linear, donor controlled fluxes.  The remainder,

12, are abiotic-^abiotic exchanges and are either linear donor or recipient

controlled fluxes.

     The three mathematical categories for classifying the various exchanges

can be generally represented as  follows;

1.  Linear, donor controlled;

     Given the conceptual interaction;
     where Xi = Donor compartment
           Xj = Recipient compartment
          Fij = Flux of carbon from "i" to "j"

     then Fij = Cij.Xi

          Cij = specific rate of transfer; gC.gC"  .At""!

     For the model, respiration, excretion, natural mortality, sedimentation

and resuspension are represented in this manner with "Cij" replaced with the
appropriate parameter.
2.  Linear, recipient controlled:

     As above, except

                  Fij = cij.Xj,

the recipient compartment controlling the realized amount of transfer.  At

present, no flux in the model is represented with this function.

3.  Non-linear, recipient controlled, donor-recipient determined;

     The general form of the equation can be given as:

                  Fij =Tij.Xj (l.-(fij.fij)}  +

-------
                                                                         150
                  where;  Fij, Xj as defined previously

                          fij = maximum specific rate of ingestion or
                                uptake; gC.gC~l.day~l

                          fij = resource controlled negative feedback term

                          fjj = self or recipient controlled negative
                                feedback term

The form of the feedback can vary depending on how a population responds

to intense predation or, oppositely, to crowding or some space related

limitation.  Without specific information relative to the form of these

feedbacks, the following general forms have been adopted;
                       i
    - Xi
a i j - Y i Jj   ,and,
                         Yjj - Xj  +

Wiegert (1975 ) discusses the various forms used in the past and Christian

and Wetzel (1978) give specific examples of changes in feedback functions

for microbial interactions using this modeling approach.


                           RESULTS AND DISCUSSION


     The ecosystem modeling project during the first year of effort has;

     a.  determined the compartmental model structure,

     b.  formulated the mathematical structure for the interaction equations
         describing compartmental coupling,

     c.  began data summaries for parameter estimation, and,

     d.  established computer software and remote terminal communications
         for model simulation and analysis.
                                                                    t
     The modeling study is designed to reflect the trophic structure of

submerged aquatic communities in Chesapeake Bay that are dominated by Zostera

marina and Ruppia maritima.  The model incorporates biologically and

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                                                                         151
ecologically realistic mathematical representations of flux pathways that

are based on testable assumptions and measureable parameters.  Hierarchical

analysis is possible at the level of processes influencing or controlling

specific fluxes as well as analysis of overall community behavior and

interaction with other bay system components.  The simulation model provides

an organizational structure and vehicle for incorporating and evaluating

the results of individual research efforts.

     The overall research incorporates three other research efforts;

     1.  Productivity and nutrient dynamics associated with micro auto-
         trophic and heterotrophic components of the eelgrass community
         including the environmental controls of light, salinity and
         temperature and measures of total community metabolish (KLW and RLW).

     2.  Within community macro-consumer dynamics (DFB and RJO).

     3.  SAV community interaction with bay consumer components; e.g.
         migratory shellfish, finfish and waterfowl (JVM).

The first model version (Fig. 1) explicitly represents these major

research efforts both compartmentally and through the mathematical structure

proposed, the postulated mechanisms controlling interactions and community

dynamics.

     The overall design is thus complimentary and highly interactive.

Specific aspects of SAV community structure and function addressed by other

CBP research efforts (e.g. R. J. Orth; M. Kemp, et al., ) will be incorporated

to the extent that the results suggest fundamental changes in design

or systems conceptualization.

     The effort is approximately 30% complete to date  (October, 1979).

The effort for the next six months will be to have a running computer version
                                                                     i,
and to have preformed a sensitivity analysis with the current model.  The

effort will identify parameters particularly sensitive to change and aid

in designing future work  (see Wiegert and Wetzel, 1979).

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                                                                           152

                               Literature Cited

Christian, R. R. and R. L. Wetzel.  1978.  Interaction between substrate,
     microbes and consumers of Spartina detritus in estuaries,  p. 93-113.
     IN;  M. L. Wiley (ed.) Estuarine Interactions, Academic Press, New
     York.

Wiegert, R. G.  1975.  Mathematical representation of ecological interactions.
     p. 43-54  IN;  S. A. Levin (ed.) Ecosystem Analysis and Prediction,
     SIAM, Philadelphia.

Wiegert, R. G.  1978.  Population models:  experimental tools for analysis
     of ecosystems.  IN;  Horn, D. J. et al. (eds.)  Proceedings of Colloquim
     on Analysis of Ecosystems.  Ohio State University Press, Columbus.

Wiegert, R. G. and R. L. Wetzel.  1974.  The effect of numerical integration
     technique on the simulation of carbon flow in a Georgia salt marsh.
     Proc. Summer Computer Simulation Conf., Houston.  Vol. 2:  575-577.

Wiegert, R. G. and R. L. Wetzel.  1979.  Simulation experiments with a
     fourteen-compartment model of a Spartina salt marsh,  p. 7-39.  IN;
     R. F. Dame (ed.).  Marsh-Estuarine Systems Simulation, University of
     South Carolina Press, Columbia.

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