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The structure and function of warm temperate estuarine fish communities

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Title:
The structure and function of warm temperate estuarine fish communities
Creator:
Schooley, James K ( James Kenneth ), 1951-
Publication Date:
Language:
English
Physical Description:
ix, 107 leaves : ill. ; 28 cm.

Subjects

Subjects / Keywords:
Community structure ( jstor )
Crops ( jstor )
Fish ( jstor )
Impoundment ( jstor )
Lagoons ( jstor )
Production efficiency ( jstor )
Production estimates ( jstor )
Respiration ( jstor )
Salinity ( jstor )
Water temperature ( jstor )
Dissertations, Academic -- Zoology -- UF
Fish populations -- Florida ( lcsh )
Fishes -- Ecology -- Florida ( lcsh )
Fishes -- Effect of water quality on -- Florida ( lcsh )
Zoology thesis Ph. D
Indian River ( local )
Genre:
bibliography ( marcgt )
non-fiction ( marcgt )

Notes

Thesis:
Thesis (Ph. D.)--University of Florida, 1980.
Bibliography:
Bibliography: leaves 101-106.
General Note:
Typescript.
General Note:
Vita.
Statement of Responsibility:
by James K. Schooley.

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University of Florida
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The University of Florida George A. Smathers Libraries respect the intellectual property rights of others and do not claim any copyright interest in this item. This item may be protected by copyright but is made available here under a claim of fair use (17 U.S.C. §107) for non-profit research and educational purposes. Users of this work have responsibility for determining copyright status prior to reusing, publishing or reproducing this item for purposes other than what is allowed by fair use or other copyright exemptions. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder. The Smathers Libraries would like to learn more about this item and invite individuals or organizations to contact the RDS coordinator (ufdissertations@uflib.ufl.edu) with any additional information they can provide.
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THE STRUCTURE AND FUNCTION OF WARM TEMPERATE
ESTUARINE FISH COMMUNITIES













BY

JAMES K. SCHOOLEY


A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF THE
UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE
REQUIRElENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY


UNIVERSITY OF FLORIDA


1980













ACKNOWLEDGEMENTS


Portions of this project were supported by a grant from the Division of Sponsored Research, the University of Florida, to Dr. Stephen Bloom. Sampling support was provided by the Merritt Island Wildlife Refuge, NASA's Kennedy Space Center, and LeFil's fish camp in Oak Hill, Florida, and is gratefully acknowledged.

Drs. Stephen Bloom, Frank Maturo, and Robert Virnstein and the staff of the Harbor Branch Foundation of Fort Pierce, Florida, provided valuable assistance in the identification of zooplankton and benthic invertebrates. This project benefited tremendously from discussions with Dr. William Carr of the Whitney Marine Laboratory of the University of Florida. Dr. Jack Ewel graciously provided advice and equipment for the calorimetric analysis and Mr. Robert Twilley provided help in the analysis of mangrove forest structure.

Field work and laboratory processing were greatly facilitated by a large group of volunteer assistants that I would like to acknowledge: David Brown, Fred Boyd, Kathy Cavanaugh, Diane Despard, J. B. Frost, Nancy Ing, Ginny Kittles, Blaise Kovaz, Beth Meerman, Jeff McGrady, Andy Roth, Bill Szelistowski, Linda Warner, Chris Wolniewicz, David Yarnell, and Milito Zapata.

The thoughtful review of early drafts of this manuscript by Drs. Frank Nordlie, Thomas Emmel, Carter Gilbert, Jerome Shireman, Stephen Bloom, and Martha Crump and Kathryn Schooley is gratefully acknowledged.


ii














TABLE OF CONTENTS


PAGE


ACKNOWLEDGEMENTS . . . . . . . . . . . . . . . . . . . . . . . .

LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . .

ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . .

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . .


STUDY AREA . . . .


METHODS. . . . . . . . . . . . . . . . . . . . . . . . . .

Physical Data . . . . . . . . . . . . . . . . . . . .
Zooplankton . . . . . . . . . . . . . . . . . . . . .
Benthic Infauna . . . . . . . . . . . . . . . . . . .
Primary Production Processes. . . . . . . . . . . . .
Fishes . . . . . . . . . .'. .. . . . .. .. . . . .
Calorimetric Processing . . . . . . . . . . . . . . .
Production. . . . . . . . . . . . . . . . . . . . . .
Respiration . . . . . . . . . . . . . . . . . . . . .
Consumption and Energy Budgets. . . . . . . . . . . .


RESULTS. . . . . . . . . . . .

Physical Environment. . .
Primary Production. . . .
Zooplankton . . . . . . .
Microbenthos. . . . . . .
Epibenthic Invertebrates.
Fish Community Structure.
Fish Community Function .


DISCUSSION . . . . . . . . . . .


Abiotic Factors . . . . . Biotic Factors. . . . . . Production. . . . . . . . Respiration . . . . . . . Consumption . . . . . . .


System Efficiencies, Turnovers, Fish Community Summary..... REFERENCES CITED . . . . . . . . .


and


Budgets


BIOGRAPHICAL SKETCH


iii


ii iv


vii


1


6


8


8
9
9
10 11 15 17
18 19


. . . . . . . . . . . . . . . . . 21


21
26 26 33
40 42 63


. . . 73


73 76 81
84 85 86 97

101


. . . . . 107


. . . . .
. . . . .
. . . . .
. . . . .
. . . . .













LIST OF TABLES


TABLE PAGE

1 Age class groupings of common seagrass and impoundment
fishes in mm of standard length . . . . . . . . . . . . . 16

2 Median water temperatures and average monthly air
temperatures during the sampling period; absolute minimum, absolute maximum and temperature ranges from
submerged maximum/minimum mercury thermometers. . . . . . 23

3 Salinity at each site monthly and total rainfall at
Cape Canaveral. . . . . . . . . . . . . . . . . . . . . . 24

4 Net primary production (kJ-m- y Y) entering the
aquatic system at site Il . . . . . . . . . . . . . . . . 27

5 Net primary production and standing crops of seagrasses at sites Sl and S2. . . . . . . . . . . . . . . . 27

6a Mean standing crop of zooplankton (Number/m3), September
to November 1978 at each sampling site. . . . . . . . . . 28

6b Mean standing crop of zooplankton (Number/m 3), December 1978 to February 1979 at each sampling site . . . . . . . 29

6c Mean standing crop of zooplankton (Number/m3), March to May 1979 at each sampling site. . . . . . . . . . . . . . 30

6d Mean standing crop of zooplankton (Number/m3), June to August 1979 at each sampling site . . . . . . . . . . . . 31

7 Site Il's average quarterly and average annual
densities and standing crops of energy for the major
groups of benthic invertebrates . . . . . . . . . . . . . 34

8 Site 12's average quarterly and average annual
densities and standing crops of energy for the major
groups of benthic invertebrates . . . . . . . . . . . . . 35

9 Site Sl's average quarterly and average annual densities and standing crops of energy for the major
groups of benthic invertebrates . . . . . . . . . . . . . 36

10 Site S2's average quarterly and average annual
densities and standing crops of energy for the major
groups of benthic invertebrates . . . . . . . . . . . . . 37


iv








TABLE PAGE

11 The values and authorities cited used to convert standing crops on a dry weight basis to standing
crops on an energy basis, for the benthic invertebrate groups common in the impoundments and seagrass
beds. . . . . . . . . . . . . . . . . . . . . . . . . . . 38

12 Percentage of the average annual standing crop of
energy for major benthic invertebrate groups at each
site. . . . . . . . . . . . . . . . . . . . . . . . . . . 39

13 Average annual density and standing crop of energy
of common large decapods at each site . . . . . . . . . . 41 14 Fish collected at site Il . . . . . . . . . . . . . . . . 43

15 Fish collected at site 12 . . . . . . . . . . . . . . . . 44

16 Fish collected at site Sl . . . . . . . . . . . . . . . . 45

17 Fish collected at site S2 . . . . . . . . . . . . . . . . 48

18 Total fish densities at each site . . . . . . . . . . . . 52

19 Fish standing crops of energy at each site. . . . . . . . 53 20 Percentage of average annual density and standing crop
of energy for the major fish species at each site . . . . 54 21 Correlations (Spearman Rank) of structural characteristics of the fish communities at each site with monthly
salinity, median water temperature and seagrass density . 56 22 Mean energy content of juveniles and adults of all
species at each site. . . . . . . . . . . . . . . . . . . 58

23a Mean energy content of common species at site Il. . . . . 59 23b Mean energy content of common species at site 12. . . . . 60 23c Mean energy content of common species at site Sl. . . . . 61 23d Mean energy content of common species at site S2. . . . . 62 24 Site I respiration and positive production values
in J/m . . . . . . . . . . . . . . . . . . . . . . . . 64

25 Site I respiration and positive production values
in J/m . . . . . . . . . . . . . . . . . . . . . . . . . 65


v







TABLE PAGE

26 Site S respiration and positive production values
in J/m . - . - . . . . . . . . . . . . . . . . . . . 67

27 Site S2 respiration and positive production values
in J/m2 . . . . . . . . . . . . . . . . . . . . . . . . . 69

28 Total annual respiration, production, and consumption
at site Il . . . . . . . . . . . . . . . . . . . . . . .87

29 Total annual respiration, production, and consumption
at site 12 . . . . . . . . . . . . . . . . . -. . . . . . 88

30 Total annual respiration, production, and consumption
at site Sl- . . . . . . . . . . . . . . . . . . . . . .89

31 Total annual respiration, production, and consumption
at site S2 . . . . . . . . . . . . . . . . . . . . . . .90


vi













Abstract of Dissertation Presented to the Graduate Council of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

THE STRUCTURE AND FUNCTION OF WARM TEMPERATE ESTUARINE FISH COMMUNITIES

By

James K. Schooley

December 1980

Chairman: Frank G. Nordlie
Major Department: Zoology

The seagrass beds of Mosquito Lagoon and the nearby impounded

marshes are the most northern portions of the Indian River and lie on the east central coast of Florida. A study of the seasonal fluctuations in water temperature, salinity, benthic invertebrate communities, and macrozooplankton standing crops was combined with estimates of annual detrital input to interpret differences in the structure and function of the fish communities in the impounded marshes and the open seagrass beds of the lagoon.

The two impounded marsh sites under study had salinity ranges of 10-280/.. and 25-380/oo during the period of this study. The ranges of water temperatures in the impoundments were 6-370C and in the seagrass beds, 8-390C during this study. Based on monthly fluctuations in salinity and temperature, it was concluded that the impoundments were no more physiologically stressful for resident fish than the seagrass beds.

Net detrital input to the shallow impoundment was 4,306 kilojoules. m-2 year-1, 75% of which came from black mangrove litter-fall. Net


vii







detrital production by the seagrasses in the open lagoon sites was
-2. -1
2,413-3,707 kJ-m -y -. The macrozooplankters most common to each site were calanoid copepods, caridean shrimp, and nematodes. Seagrass beds had higher densities of caridean shrimp and brachyuran larvae. The benthic infauna was dominated by bivalves in the impoundments and polychaetes in the seagrass beds. The absence of large decapods, especially blue crabs, and the limited fish fauna of the impoundments are suggested as reasons for the vastly different benthic communities found in the two habitats.

Structurally, the fish communities of the impoundments were dominated by several species of fishes in the order Atheriniformes. Most common were Cyprinodon variegatus, Poecilia latipinna, Gambusia affinis, Lucania parva, and Menidia peninsulae. The clown goby, Microgobius gulosus, was also consistently found. In the seagrass beds, the dominant resident community members were Lucania parva, Nenidia peninsulae, Microgobius gulosus, Gobiosoma robustum, and Syngnathus scovelli.

Significant seasonal recruits to the seagrass beds, primarily represented as juveniles, were Lagodon rhomboides and Bairdiella chrysoura.

Average fish densities in the impounded marsh were 16.5-27.5 (Ind/m2 ) and in the seagrass beds, 3.6-7.3 (Ind/ m2). Average fish standing crops were 53.7-58.5 kJ/m2 in the impoundments and 5.5-6.9
2
kJ/m in the seagrass beds. Complexity of community structure was positively correlated with median water temperature at all sites. At only one of the two seagrass sites was there a significant positive correlation between community structure and seagrass density.

Functionally, the impoundment fishes were estimated to have

consumed 992-1,059 kJ.m- . 1, respired 512-655 kJ.m-2 .y-1 and had a net


viii







production of 192-281 kJ-n-2.y -1. In contrast, the seagrass bed fishes are estimated to have consumed 91-118 kJ-m-2.Y-1, respired 60-81 kJ-m- 2y 1, and had net fish productions of 13 kJ.m-2.y-1. The turnover rates of energy for the impoundment fishes were 3.6-5.2 per year, while the seagrass beds were 1.9-2.4 per year. The impoundment fishes appear to be more efficient at converting consumed energy into net fish production than the seagrass bed fishes. The efficiencies of other energy transfers, the influence of herbivore/detritivores, and fish generation times are discussed in comparing the two fish community types to each other and to other aquatic systems in general.


ix













INTRODUCTION


Few researchers have attempted to assemble an ecosystem model for shallow estuarine systems. Notable attempts at structurally and functionally describing these complex systems in terms of energy flow are Day et al. (1973) for Barataria Bay in Louisiana, Odum et al. (1974)

for Crystal River, Florida, and Thayer et al. (1975a) for the grass beds of the Newport River, North Carolina. Except for the Crystal River study, most models are the result of the synthesis of community and population studies, only some of which may have contemplated integration into an ecosystem model.

In attempting to synthesize previous studies into models, structural characteristics are often better understood than are functional characteristics of the various communities or populations within the ecosystem (Day et al. 1973). This is also usually the case for estuarine fishes. Even though a variety of structural references concerning species composition, seasonality, and, in some cases, density, is available for most larger estuarine systems, very little information on the energetic functioning of fishes is available. These functional characteristics would include estimates of respiration, production, and consumption. Excellent contributions to our understanding of the consumption process, and ultimately energetic functioning, include the Harringtons' (1961) food selection study of salt marsh fishes, Oduni and Heald's (1972) trophic analysis of the North River estuary in south Florida, Carr and Adams' (1973) classic analysis of the ontogenetic


1





2


feeding changes of fishes in seagrass beds of west Florida, and

Whitfield's (1980) work on the energy flow in a south African estuary. The work by Adams (1976a,b) on the fish communities in Zostera beds in the Newport River estuary, North Carolina, is an excellent example of a study that structurally and functionally describes a community and is later integrated into an ecosystem model (Ferguson and Adams 1979).

One estuarine system that only recently has come under intensive study is that of the Indian River on Florida's east central coast, the northern portion of which is shown in Figure 1. Gilmore (1977) has done a summary of the geography and hydrology of the Indian River in his review of the fish fauna of the region.

Prior to the mid-1950's, the high marshes within the Indian River were accessible to fishes of the open lagoon. However, since then, nearly all high marsh has been isolated from the lagoon by earthen dikes for mosquito control purposes (Provost 1969, 1973). On Merritt Island, this resulted in over 22 hectares of marsh being isolated, as

well as partitioned by these dramatic management practices (Provost 1969, 1973). Snelson (1976) has done a preliminary survey of the fishes of the various impounded marsh habitats of northern Merritt Island. The impact of this impoundment on the entire estuarine fish community has never been evaluated. Without the experimental control of a similar large estuary with an unimpounded marsh such a determination

would be difficult.

One aspect of fish community ecology that is testable within this modified system is the impact of this isolation on the populations of several species that are common to both the impoundments and seagrass beds (Snelson 1976, Gilmore 1977). These populations will serve as



























Figure 1. The northern Indian River and sampling locations; o = impoundment 1 (Il),
e = impoundment 2 (I2), 0 = seagrass bed 1 (Sl), * = seagrass bed 2 (S2).










80*W
PENSACOL A --F>LE30* N

0
- TAMPA
GULF OF MEXICO







ATLANTIC OCEAN
HAULOVER










TITUSVILL CAUSEWAY








CAUSE SAN


Z ERRITT-SLANDCANAVEAL


0K
0
BIRD
















Is.



cq





5


excellent ecological indicators of the relative differences in structure and function between fish communities in the impounded marsh and those in the seagrass beds.


The objectives of this study are

(1) to examine and compare the structure and energetic functioning of fish communities in impounded marsh and open

seagrass beds;

(2) to elucidate relationships between the observed properties

of the fish communities and abiotic and biotic factors;

(3) to characterize the functional aspects of the fish communities in terms of efficiencies of transfer in order to

compare the systems studied to other aquatic systems in

general;

(4) to provide information useful in developing ecosystems

models of the impounded marsh and seagrass beds.













STUDY AREA


The northern Indian River and Mosquito Lagoon are shown in Figure 1. The term "river" is a misnomer. Indian River is a large, shallow, mesohaline lagoon that extends 250 kilometers along the east central coast. The lagoon is separated from the ocean by a barrier island that is cut in five places by artificial inlets. In the northern portion of the system this barrier island is at its widest and is known as Merritt Island. The Mosquito Lagoon is separated from the rest of the Indian River by a second strip of land. This land has been cut at the Haulover Canal to form a passageway for the intracoastal waterway. The closest access to the ocean from Mosquito Lagoon is through the Ponce de Leon Inlet, 80 kilometers north of Haulover Canal, just off the map shown in Figure 1.

The average water depth of Indian River is 1.5 m, with the maximum depths in areas dredged for channels, harbors, and land fill. The bottom of the lagoon is covered by extensive seagrass beds, dominated by Halodule wrightii and Syrinogodium filiforme. In the northern part of the system (Fig. 1), tidal fluctuations are insignificant; the major water movements are the result of wind-driven circulation (Dubbelday 1975). Lasater (1975) reported that in Mosquito Lagoon, salinity ranges from 21-360/o, with a yearly average of 31.1/oo. Because of the lack of significant fresh water input, the salinity of the lagoon at any given time represents a balance between evaporation and local precipitation (Lasater 1975).

6





7


Two seagrass beds within the Mosquito Lagoon were studied. The first, S1, is located in Eddy Creek at the southern end of the lagoon, where water depth was approximately 0.5 m. The second seagrass site, S2, was located off of an area known as Van's Island, approximately 18 km from Sl. Water depth at S2 was approximately 0.6 m.

In contrast to the relative homogeneity of the system of seagrass beds, the impounded marshes of [erritt Island and the barrier island east of Mosquito Lagoon do not have a uniform flora either in species composition or species density (Snelson 1976). This is due partially to variations in salinity and water level resulting from differing degrees of isolation among the impoundments. In the impoundment at the southern end of the Mosquito Lagoon studied here (Ii) the marsh was broken by large expanses of water bordered by stands of black mangrove (Avicennia germinans); however, some white mangrove (Laguncularia racemosa) and button mangrove (Conocarpus erecta) were also present. The open waters were found to have seasonal growths of Chara, which in some locations filled the water column.

The northern impoundment canal (12) was located approximately

200 m from site S2. This canal, formed by draglinning, is nearly continuous around the periphery of Van's Island and is approximately

1.25 m deep with a width of 15 to 20 m. During the dry season, it is the only standing water in the area sampled; however, during the rainy season this canal is only a part of the large marsh surface covered by water. The dominant vegetation was low-fringing black mangroves with some button mangroves along the dike and occasional growth of Chara.













METHODS


Sampling was done once each month during the period July 1978 through August 1979 for sites I, Si, and S2. Site 12 was sampled monthly from August 1978 through August 1979. Each sampling effort consisted of measuring air and water temperature, salinity, depth, and submerged macrophyte density and collecting samples of macrozooplankton, fish, and larger epibenthic invertebrates. Benthic infauna were collected quarterly at each site in October 1978 and January, April, and July 1979. Site 11 was also sampled in May 1979.


Physical Data

Physical data collected at each site included measurements of air temperature in the shade, water temperature, salinity, and water depth in the areas sampled for fish. [aximum-minimum thermometers were submerged at sites Il, 12, and S2, and readings were taken each month and the thermometers reset. Salinity samples were taken at mid-water depth and analyzed using a temperature-correcting optical refractometer. In November 1979, surface sediment samples were taken at Il and S2 and the percentage of combustible material determined by ignition in a 475*C oven for 8 hours.

Rainfall and average monthly air temperatures are from recordings taken at Patrick Air Force Base 60 km south of Mosquito Lagoon.


8




9


Zooplankton

Each month, three replicate 10-m length tows were taken at each site using a 363 p mesh net with a diameter of 0.3 m and length of 1 m. The contents of each tow were individually preserved in 5% buffered formalin. Beginning in October ctenophores were counted prior to preservation. Ctenophores in earlier samples broke down rapidly and are, therefore, underestimated in data from July through September 1978.

Specimens were identified only at the most practicable taxonomic level during sorting and counting. Prior to sorting samples with a large amount of flocculent material, a small amount of dissolved rose bengal was added to stain the plankton and improve sorting efficiency.

The mesh size and length of tows were expected to produce comparatively dilute plankton samples but were considered adequate for the purpose of making a qualitative comparision between the impoundments and seagrass beds.


Benthic Infauna

Sampling the benthic infauna was done at a random location

adjacent to the areas seined for fish. Five adjacent cores were taken from this area using a PCV coring tube with an inner diameter of 10.5 cm driven to a depth of 10 cm of solid sediment. Each core sampled 86.6 cm2 of bottom area. At site Il this produced a sample of 7-10 cm of flocculent material on top of the 10 cm of consolidated sediments. Sites 12, Sl, and S2 did not have deep layers of unconsolidated material.

The contents of each core were sieved in the field to retain materials larger than 500 microns. The retained material was




10


preserved in 10% buffered formalin. After sorting and identification

of core contents, representative subsamples were taken to determine dry weights and, for some gastropods and bivalves, ash-free dry weights per individual.

Standing crops of dry weights were converted to standing crop energy units by using published energy content values (Cummins and Wuycheck 1971, Thayer et al. 1973, Whitfield 1980).


Primary Production Processes


The above-ground standing crop of macrophytes from five randomly thrown 0.25 m2 quadrats was harvested each month. Samples were taken in waters 50-75 m from shore at sites Sl and S2, along the edge of the canal at 12, and 25-50 m from shore at Il. The harvest from each toss was returned to the lab, where shell and detrital materials were rinsed off prior to drying to constant weight at 80'C.

The yearly net primary production of seagrass at sites Sl and S2 was calculated as two times the maximum standing crop (McRoy and Mcrillan 1977), assuming 1 mg dry weight is equivalent to 16 joules. The contribution of epiphytes to seagrass community net production was not evaluated; present work by the Harbor Branch Consortium (R. A. Gibson, personal communication) may shed some light on the contribution of epiphytes to net production within the seagrass beds of the Indian River.

Net primary production for site Il was computed in two components: the contribution of the green algae Chara and the litter fall from the mangroves, primarily blacks (Avicennia). Production for Chara was calculated at 1.5 times the maximum standing crop (Rich et al. 1971);




11


mangrove litter production was calculated after determining a leaf area for the mangroves during the summer of 1979. Leaf area was calculated using the modified plumb-bob technique used by Benedict (1976). The technique was applied at five random sites, with ten replicates at each site. Production was then calculated using a ratio of leaf area index to litter production for Florida mangrove forests derived from Pool et al. (1974). Based on forest descriptions in Pool et al. (1974) leaf turnovers per year were assumed to be 1.0 and the ratio of leaf litter to wood litter to be 3:1. Dead leaves prior to falling were assumed to contain 20.17 J/mg (Heald 1969) and twigs 17.86 J/mg (Golley 1961) on a dry weight basis.

The percentage of marsh covered by open water versus mangrove canopy was determined by planimetry (cut and weigh) of recent aerial photographs of the Il sampling area. This provided a proration to use in computing total marsh production from Chara and mangrove production data.

At site 12, the impoundment canal, the input of detritus was considered to be a complex interaction, varying with the season, of variable water transports to and from the impoundment flats. Therefore, an estimate of net primary production available within the canal habitats would be premature, based only on limited Chara and fringing mangrove production data.


Fishes

Shrimp, crabs, and fish were quantitatively sampled each month at sites Il, Sl, and S2 by open-water seining as shown in Figure 2. Each net was 10 m in length, with a bar mesh of 3.18 mm. The sampling team































Figure 2. Diagrammatic aerial view of the open water sweep seine techniques; see text
for explanation. Open circles = sweep net, closed circles = barrier net.













E



E0


(D


0000 00*0*t0. o 0 Co 0 0 00 *0*** 0 0 0 0 0~0 ooo~o*000


OAIO:*


13


S
E mY I


0







0*.


u




14


proceeded as a tight group to the edge of the area to be sampled, and immediately deployed the two nets, a sweep and a barrier, at right angles to each other. The barrier net was set perpendicular to the beach area and the sweep net, set on the deep water end of the barrier, was swept toward the shallows. The 10-m sweep net was tethered at a fixed distance of 6.1 m, sampling a bottom area of 33 m2. The two nets were pursed and removed from the water for sorting. Site 12, the impoundment canal, was sampled using a beach seine. The sweep net was run out 6.1 m from the shoreline and perpendicular to it. The net was then swept to the beach. This covered 33 m2 of area, as in the openwater seining. Because the canal was approximately 1.1 m deep at the end of the 6.1 m sweep net, the volumes of water swept in the two techniques were comparable. Three replicate quantitative samples were taken at each site.

Early attempts using a portable drop net (Adams 1976a) that

sampled an area of 9 m2 were found to be very labor-intensive and did not significantly alter the density, species number, or size classes found using open water seining. Gilmore et al. (1976) discussed the effect of sampling with drop nets for Indian River seagrass systems. He pointed out that due to the size of open sand and grass patches, drop samples can be strongly biased, while larger samples from seining cover a greater diversity of open sand and seagrass areas may be less biased. However, extremely large seines can underestimate several groups such as the gobies and pipefishes. The techniques used here are

an attempt to compromise between drop-net and large sweep-net techniques.

Fish and invertebrate species collected were bagged in plastic

and stored on ice. Samples were returned to the lab for processing as




15


soon as possible. Fish and invertebrates were sorted and identified; the fish were partitioned into standard length-size ranges of 5 mm, i.e. 0-5 mm, 6-10 mm, etc; crabs were measured across the width of the carapace. After drying for 48 hrs in a forced air oven at 80*C, dry weights were recorded for each size class group for each species of fish, for the total of each shrimp sample, and for each crab individually.

A qualitative seine sweep was taken each month at sites Sl and S2 with a 20 m bag seine, also of 3.18 mm bar mesh. An area of 10002000 m2 was swept at each site. Fish and invertebrates collected were sorted and any species not found in the quantitative seine were preserved in 25% buffered formalin. The remaining catch was subsampled to augment the various size class categories of species collected in the quantitative seines to provide an adequate sample size, in terms of mass, for calorimetry. The samples were separately bagged and also stored on ice for immediate processing and drying on returning from the field.


Calorimetric Processing


After recording dry weights of individual size classes for each fish species, the various size classes of the dominant species were grouped into age classes (Table 1) according to the technique of Adams (1976a). These samples were then processed according to the general procedures outlined by Cummins and Wuycheck (1971); however, no carbonate fractions were determined. For determination of ash-free dry weights, subsamples were burned at 475C for four hours to avoid burning off carbonates (Paine 1971). Calorimetry was done using an




16


Table 1. Age class groupings of common seagrass and impoundment of fishes in mm of standard length.



Age Class
Species
Pre-juv Juvenile Adult Rep Adult


Anchoa mitchilli 50 >50
Archosargus probatocephalus 25-50 >50
Bairdiella chrysoura 10-85 >85 >130
Cynoscion nebulosus 25-200 >200
Cyprinodon variegatus 10-14 15-24 25-35 >35
Eucinostomus sp. 15-55 >55
Fundulus grandis 15-30 >30
Gambusia affinis 520 >20
Gobiosoma robustum 9-15 >15
Lagodon rhomboides 15-50 51-85 >85
Leiostomus xanthurus 17-85 >85
Lucania parva 8-25 >25
Lutjanus griseus 10-175 >175
Menidia sp. 20-60 >60
Microgobius gulosus 530 >30
Paralichthys albigutta 595 >95
Poecilia latipinna <20 >20
Strongylura notata 45-200 >200
Syngnathus scovelli 560 >60
Trinectes maculatus 18-45 >45




17


automatic adiabatic calorimeter equipped with a digital thermometer, printer, and prograner (Parr Instrument Company, Moline, Illinois). Operating procedures followed the Parr procedures manual directly (Parr 1969). Two 1 g replicate samples were taken for percent water and ash content determination at the same time the three replicate 1 g pellets were pressed prior to bombing. Over 90% of the materials tested gave a coefficient of variation ("C.V.") of less than 1%, using three replicates. The C.V. was less than 3% for 99% of the samples. Golley (1961) and Paine (1971) recognize a coefficient of less than 3% as a satisfactory variation for biological materials. Results are expressed as joules per milligram of ash free dry weight.


Production


As defined by Ivlev (1966), production is the total amount of fish tissue produced during any given time interval , including that of individuals that did not survive to the end of that interval. Monthly production is then calculated as the product of the growth per individual and fish numerical density.

Production for each species was calculated after Ricker (1946) and Allen (1950) as


P = GB

where

P'1 W2 - wn
G = At is the coefficient of instantaneous growth,


_ B1 (e G-Z 1)
B = G-Z) is the average biomass, and




18


Z -(n N I zn N2) is the instantaneous coefficient of =At population change attributable to
mortality and migration,

and W and W2 are the mean weights at time ti and t2, respectively, and N1 and N2 are the numbers of fishes present at times ti and t2, respectively.

Day et al. (1973), Adams (1976b), and Chapman (1978) discussed some of the important assumptions of the applications of this model. As Adams (1976b) pointed out, estuarine and seagrass fishes usually show marked immigration and emigration which affect estimates of N. This is probably more significant at sites Sl and S2 than at Il and 12. However, Chapman (1978) pointed out that there is no need to correct production data for the immigration and emigration of fishes, provided fish density and size-class specific growth are estimated often enough to assess abundance and growth during the sampling period. Day et al. (1973) used three-week sampling intervals, while Adams (1976a) used four-week intervals as done in this study.


Respiration

The resting energy of metabolism was estimated from Winberg's (1956) equation, Q = 0.321 W0.79, as a general equation for marine fish at 20'C. Metabolism for each species was calculated at an average weight per individual at the median water temperature during the

sampling period by applying Krogh's (1916) temperature correction factors. This rate of oxygen use per hour by one average-weight individual weighing X g dry weight was converted to a population total of joules burned per month at each site using a conversion factor of 14.07 J/mg of oxygen (Mann 1978).




19


The energy cost specific to utilization of food, apparent specific dynamic action, and the metabolic cost of foraging for food were both found to be significant portions of the energy budgets of fish populations studied by Kerr (1971a,b,c). Reviews by Webb (1978) and Mann (1978) discuss the relationship between resting metabolism and true energy costs in nature. According to Mann (1978), Winberg II, a doubling of the equation above (Winberg I), appears to be a useful approximation of the metabolism of a fish which optimizes its growth rate in nature (Edwards 1968, Ware 1975). Winberg II is used here as the estimate of respiration within the fish community.


Consumption and Energy Budgets


Annual energy consumption per species in both habitat types was calculated as a percentage of the sum of respiration plus production. Winberg (1956) found assimilation efficiencies for freshwater fishes between 76% and 96.6%. The average values assumed were 85% of calories of the diet were assimilated and 15% lost as feces. He also argued that, with a range of 3-7% of the energy lost as urine added to fecal loss, a total of 20% of ingested energy was lost through egestion and excretion.

Winberg's equation as applied here is


C = 1.25 (P + R)

where


C = annual consumption of energy, R = annual metabolic energy loss,

P = annual production energy.




20


Community annual consumption is then compared ,between the various sites. Interspecific comparisons of consumption should be done cautiously, due to the broad range of assimilation efficiencies found for different fish species in nature (Webb 1978).

Fish community energy budgets for each site were then constructed by the addition of each species' totals for consumption, production, and respiration during the year. Ecological efficiencies were then calculated for each community and used to compare communities.


A













RESULTS


Diagrams summarizing the major environmental influences, primary production sources, and energy flows for the impounded marshes and seagrass beds are presented in Figure 3. These diagrams depict the conceptual framework for presentation of the results of this study and the subsequent discussion of each community.


Physical Environment


The average values and the ranges of temperature and salinity for the four sites show an interesting pattern (Tables 2 and 3). The yearly range of temperatures (Table 2) found in the two impoundment habitats, Il and 12, and one seagrass bed, S2, were nearly identical; however, the average range per month of temperatures experienced at 12 was significantly smaller (Student's t, p < 0.05) than those ranges for Il and S2. This reduced environmental flux at 12 is assumed to result from the deeper water buffering rapid daily temperature fluctuations. Site 12 had narrower average monthly temperature ranges than site S2, but not significantly so. Overall, water temperatures closely paralleled the average air temperatures and the two were roughly equal during January, February, and March.

Significant differences were found in the average salinities at the four sites. Site 11 was significantly lower than the other three sites (Student's t, p < 0.01). Site 12 was significantly higher than


21



















MAJOR ENVIRONMENTAL PRIMARY PRODUCTION


SOURCES


ENERGY FLOWS


INFLUENCES







Insolation Nutrients Wind


Sediment





Insolation Nutrients


Summary diagrams of generalized seagrass bed and impounded marsh energy flows into the fish community.


Rooted Macrophytes - Detritus/Microbes - Macrobenthos Tertiary Consumers



Epiphytic Diatoms I

Microhen tho

Phytoplankton Zooplankto econdary Consumer





Rooted Macrophytes Nerbivorous/
and Alqae Detritivorous Fishes 'Tertiary Consumers
I -- Mac ohen thos
Mangroves - Detri tus/Microbes Macro nI :!!

Microbenthos
Phytoplankton Zooplanktnn Secondary Consumers


Rainfall


SEAGRASS BEDS


IMPOUNDED


MARSHES


Figure 3.


r\)
N3




23


Table 2. Median water temperatures and average monthly air temperatures
during the sampling period; absolute minimum, absolute maximum
and temperature ranges 'from submerged maximum/minimum mercury
thermometers.



Water Temp(*C) Air Temp('C)
Year & Month Ii 12 S2 Cape Canaveral


1978 August ---- ---- 31.5 25.6
September 31.0 31.0 31.0 25.0
October 26.0 30.0 24.0 22.0
November 23.0 23.0 22.5 22.0
December 21.5 22.5 20.4 17.0
1979 January 15.0 15.0 ---- 15.0
Februrary 16.4 16.8 17.5 15.0
March 18.5 19.3 18.5 18.0
April 24.0 25.5 24.5 22.8
May 27.5 27.0 ---- 23.9
June 29.0 31.5 29.0 26.7
July 20.5 33.0 ---- 28.3
August 31.0 31.3 ---- 27.2



Absolute minimum 6.0 8.0 8.0
Absolute maximum 39.0 37.5 39.0
Maximum monthly 17.5 15.5 19.0
range width
Average monthly 14.7 10.8 15.3
range width




24


Table 3. Salinity at each site monthly and total rainfall at Cape Canaveral.



Salinity (0/oo) Rainfall (mm)
Year & Month 11 12 Si S2 Cape Canaveral


1978 August 14 38 35 38 32
September 16 38 32 36 88
October 17 36 38 36 56
November 20 36 34 34 16
December 28 38 38 38 103
1979 January 10 28 18 25 178
Februrary 12 32 20 33 32
March 13 32 22 34 39
April 18 34 ---- 38 19
May 15 32 24 30 142
June 20 35 32 35 116
July 18 34 35 34 85
August 16 36 36 37 228



Average 16 34 30 34

Range 10-28 28-38 18-38 25-38




25


Sl (Student's t, p < 0.01), while Sl and S2 were not significantly different from each other.

As was the case with temperature, the stabilizing influence of greater water depth on yearly fluctuations is seen in the narrower range of salinity found at site 12, as compared to the other three sites. In comparing Sl and S2, the greater range of salinity at Sl is believed to be due to the isolation of the shallow portion of the lagoon where site Sl is located (Eddy Creek). This possibly reduces mixing and, consequently, the waters of Sl are diluted relatively more during periods of heavy rainfall. The most remarkable change in salinities was a drop of 20/o, which occurred at Sl from December to January due to the heavy rains the area received in late December and early January.

The seasonality of rainfall in the Mosquito Lagoon area would appear to modify the rain's influence on depressing salinity in the system. Two peak periods of rainfall were observed, winter and early summer. During the winter, when rates of evaporation were relatively low, salinity was markedly depressed by heavy rainfall and did not recover rapidly. However, during the summer, a period of rapid evaporation, heavy rains did not depress salinities to the same degree as winter rains, nor for as long a time. Therefore, the seasonality of rainfall, as well as amount, markedly affected both the level and fluctuations of salinity within the shallow water systems studied.

The percentage of combustible organic material in the surface

sediment at I was over five times greater than that found at S (22.6% vs. 3.9%). With sample sizes of 9 and 8, respectively, this difference is highly significant (Student's t, p < 0.001). Therefore, the yearly





26


accumulation of detrital material is assumed to be much greater within the impoundments than in the shallow seagrass bed. However, some of the detritus originating in the shallows may possibly be transported from the seagrass beds and deposited in deeper waters of the lagoon. Thomas (1974) found amounts of organic carbon in the sediments of barrow pits and infrequently dredged portions of the intracoastal waterway to be 2 to 3 times higher than the shallower seagrass beds. However, the percentage of net detrital production exported to deeper water storage in the open lagoon is not known.


Primary Production

Estimates of net primary production for three sites are presented in Tables 4 and 5. The ratio of mangrove production to Chara production within the impoundments was approximately 4:1. The ability to extrapolate from the estimates for Il to the entire impounded marsh has not been demonstrated. Analysis of infrared aerial photographs to determine plant surface areas within the impoundments is now being attempted using facilities of the Kennedy Space Center. However, the spectral sensitivity of films presently available does not appear to be great enough and will delay estimates until a great deal of ground-truth work is done.


Zooplankton

The twelve months of zooplankton collections were divided into four seasonal quarters (Table 6) based on rainfall and air temperature patterns (Tables 2 and 3). By taking the average of the collections for each of the three month periods, some of the temporal




27


2 -1
Table 4. Net primary oroduction (kJ.m .y ) entering
the aquatic system at site I1; units civen for
each value, numbers in parentheses are one
standard error, N--sample size.


Site Il

Mangrove


Leaf area index
Leaf weight/leaf area (g/m2)
Net production as litter into
the aquatic system (kJ-m-2.y-1)
Percentage of rarsh covered
by mangroves

Net Production (kJ-m-2.y-1)



Chara

Maximum standing crop (g/m2) Minimum standing crop (g/m2)
Net production in open
water (kJm-2.y-1)
Percentage of open water

Net Production (kJ-m-2.Y-1) Total marsh net production
(kJ.m-2.y-')


1.66 (0.47), N = 50 180 (51), N = 10 7463


3433


63.98 (51.66), N = 5
0.0, N = 5 1648 (1331) 53%

873 (705)

4306


Table 5. Net primary production and standing crops of
seagrasses at sites Si and S2; numbers in
parentheses are one standard error, N--sample
size.




Si S2


Maximum standing crop (g/m2) 75.83 (24.37), 116.5 (20.14)
N = 5 N - 5

Minimum standing crop (g/m2) 12.11 (4.4), 8.74 (6.34),
N - 5 N = 5

2
Net Produc'ion (kJ-m . y 2413 (387) 3707 (3120)




28




Table 6a. [lean standing crop of zooplankton (Number/m3), September to November 1978 at each sampling site.



Taxa II 12 Si S2


Cnidarians --- 1.6 0.2 1.0
Nematodes 21.0 0.8 0.5 2.8
Polychaetes 0.3 0.6 0.8 0.3
Gastropods 2.0 0.2 --- --Bivalves 0.2 --- --- 0.6
Ostracods 12.0 0.2 0.2 2.7
Copepod larvae --- --- 0.7
Calanoid copepods 1.0 1.0 1.7 5.6
Cyclopoid copepods --- --- 0.2 0.3
Harpacticoid copepods --- 0.2 1.0 1.0
Cypris larvae --- 0.2 --Mysids --- --- 0.2 --Amphipods 0.5 --- --- --Caridean shrimp 1.2 0.4 2.0 15.1
Brachyuran larvae 0.2 0.2 1.0 1.0
Larvaceans --- --- 3.3 --Chaetognaths --- 0.2 0.2 2.1
Other taxa 1.6 --- 0.8 0.7


40.0 5.1


12.3 33.2


Tota I




29




Table 6b. iean standing crop of zooplankton (Number/m3), December 1978 to February 1979 at each sampling site.




Taxa Ii 12 Si S2


Cnidarians --- --- --- 0.6
Ctenophores --- --- 0.1 1.9
Nematodes 183.0 6.1 25.5 13.0
Polychaetes 0.2 2.7 1.0 1.0
Gastropods 1.4 --- --- --Bivalves --- --- 1.1 0.7
Ostracods 1.6 0.2 8.8 3.5
Calanoid copepods 4.6 85.0 8.8 9.1
Cyclopoid copepods 1.2 0.3 2.1 0.4
Harpacticoid copepods 2.4 1.9 1.7 1.0
Cypris larvae --- --- --- 0.1
Mysids --- 0.7
Cumaceans --- 0.2 0.3 0.3
Isopods 0.2 0.2 3.9 5.7
Amphipods --- 2.4 3.9 1.1
Caridea'n shrimp 0.4 1.1 73.4 33.9
Brachyuran larvae --- --- 0.5 0.1
Pycnogonids --- --- 0.1 0.1
Hemipteran exoskeleton 0.4 4.0 --- 0.7
Mosquito larvae --- 2.2 --- --Chaetognaths --- --- 0.7 1.0
Fish eggs --- 1.3 0.1 --Fish larvae --- 0.8 1.0 0.3
Other taxa 3.0 0.1 0.1 0.4


197.9 107.6


Tota I


134.o




30


Table 6c. Mean standing crop of zooplankton (Number/m3 ), flarch to lay 1979 at each sampling site.



Taxa II 12 Si S2


Cnidarians 1.1 2.8 --- 0.6
Ctenophores --- --- 0.01 15.7
Nematodes 282.3 15.7 17.6 34.0
Polychaetes 1.4 1.4 0.6 1.1
Gastropods 0.3 0.6 0.2 5.7
Bivalves --- 0.2 1.1 0.8
Ostracods 1.1 0.8 4.6 1.9
Copepod larvae 1.0 --- --- --Calanoid copepods 37.1 152.8 56.4 2.7
Cyclopoid copepods 5.0 0.3 --- --Harpacticoid copepods 6.4 1.7 0.9 3.5
Isopods --- 0.3 0.5 1.4
Amphipods 0.6 0.6 0.6 1.1
Caridean shrimp 3.0 3.3 51.9 25.8
Brachyuran larvae 0.3 1.9 43.7 2.4
Chaetognaths --- --- 3.9 0.2
Fish eggs --- --- 0.2 --Fish larvae --- 0.2 1.7 0.6
Other taxa 0.3 1.9 0.2 0.8


339.9 184.5


184.4 98.3


Tota 1





31


Table 6d. Mean standing crop of zooplankton (Number/m3 ), June to August 1979 at each sampling site.




Taxa Il 12 Si S2


Cnidarians --- --- 0.3 2.7
Ctenophores --- --- 9.1 0.2
Nematodes 48.4 4.7 21.2 27.8
Polychaetes --- --- 0.9 2.0
Gastropods --- --- 1.4 1.7
Ostracods 1.3 --- 4.6 3.0
Copepod larvae 0.8 --- 0.2 0.2
Calanoid copepods 127.8 8.6 16.5 133.6
Cyclopoid copepods 1.1 --- 0.8 0.5
Harpacticoid copepods 2.4 0.5 4.1 9.9
Isopods --- --- 1.6 .7.5
Amphipods 0.2 0.3 --- 1.3
Caridean shrimp 3.5 0.2 14.8 64.6
Brachyuran larvae 3.3 4.7 69.3 4.1
Hemipteran exoskeletons --- 1.1 --- --Chaetognaths --- --- 0.5 3.8
Fish eggs --- --- 12.3 --Fish larvae --- --- 1.1 0.9
Other taxa 0.03 0.4 1.1 1.8


188.7 20.5


Total


159.8 265.3




32


variations in standing crops of zooplankton is lost, making the sites, in some cases, appear more similar. However, the zooplankton here are being used to interpret broad aquatic community differences in the four sites studied, and this loss of information is not considered critical.

The most abundant groups found in the water column were nematodes, calanoid copepods, and caridean shrimp. Several other groups that were not as abundant but showed noticeable site and/or seasonal differences in distribution were ostracods, brachyuran larvae, and chaetognaths. Several groups such as the nematodes and harpacticoid copepods are not normally considered zooplankton, but are so considered here because, due to shallowness and windmixing, they are constantly in the water column. The exclusion of such forms would not seem appropriate when trying to reflect on the biological activity of the water column and, ultimately, how such differences might relate to fish-community structure and function.

The water column at site Il was dominated by nematodes, except in midsummer when large swarms of calanoid copepods appeared. At this same time caridean shrimp and brachyuran larvae were reaching their peak abundances at site Sl.

Site 12 was characterized by the sharp seasonality of calanoid

copepods. During the spring, densities peaked, only to crash dramatically by midsummer. Midsummer in general was a period of very low plankton standing crop at 12 relative to the other sites.

The seagrass sites were distinguished somewhat from the impoundment sites by the greater densities of caridean shrimp and brachyuran larvae and were distinguished between themselves on the seasonality




33


of these same taxa. Caridean shrimp densities reached a peak at Sl during the winter and spring, whereas they peaked at S2 in midsummer. Brachyuran larvae were much denser at Sl than any other site, and reached a peak density during midsummer as they also did at S2. Sites Sl and S2 were also distinguished by consistent chaetognath populations.

Overall, the spring was the period of peak zooplankton densities for both impoundments, while one seagrass bed peaked in spring and the other in midsummer.


Macrobenthos

The results of the quarterly sampling at each site are shown in Tables 7, 8, 9, and 10. The values shown in Table 11 were used to convert dry weight to joules. Nematode densities were converted to biomass using 1.46 pg/nematode (Day et al. 1973) and copepod densities were converted using 18 wg/copepod, a general value cited by Day et al. (1973). Based on average annual standing crops of energy, sites Il and S2 were significantly lower than sites 12 and Si (Student's t, p < 0.01). This is also reflected in the number of major storages, here defined as taxa with average standing crops in excess of 2 kJ/m2 at each site. Diversity of storages is assumed to be indicative of the diversity of energetic pathways within the system. Sites II, S2, 12, and Sl had 3, 6, 7, and 10 such major energy storages, respectively.

The contributions of major taxa to the annual average standing crop are shown in Table 12. Both impoundment sites were dominated by bivalves, whereas the seagrass sites had a much larger storage in polychaetes and, in general, had greater equitability between storage compartments. Major storages unique to the two site types were








Table 7. Site Il's average quarterly and average annual densities (Nlumber/m 2) and standing crops of energy
(kJ/m2) for the major groups of benthic invertebrates.



October January April July Average
Taxa
Density Energy Density Energy Density Energy Density Energy Density Energy


Polychaeta Oligochaeta Amphipoda Decapoda Isopoda Copepoda
Cumacea Ostracoda Gastropoda Bivalvia
Nematoda Sipuncula


23 0.16


69 0.48


92 2.30


462 23
162 69
416


2.41 0.08 2.51
6.04
4.13


254 277


23
139 23


1.15
1.00


2.01 1.38 <0.01


92 4.33


254 23
611 23


<0.01 88.33
35.56
<0.01


93 69
382


<0.01 60.56
16.47


3996 154.80


23 0.39


393 <0.01 83 25.91


18
7
5
2 16


2 18
2
126


5 0.93
5 0.54
8 0.75
3 2.01
2 1.95
6 <0.01 3 1.00
5 <0.01 3 37.22 8 58.18 6 <0.01 6 0.10


1676 92.21 4296 162.91


Annual Average 2020 102.77


CA)


1007 28.06


Totals 1095 126.83






Table 8. Site 2's average quarterly and average annual densities (Number/m2 ) and standing crops of energy
(kJ/m) for the major groups of benthic invertebrates.



October January May July Average
Taxa
Density Energy Density Energy Density Energy Density Energy Density Energy


Polychaeta Oligochaeta Amphipoda Decapoda Tanaidacea


Isopoda Copepoda Cumacea Ostracoda Gastropoda Bivalvia Platyhelminthes Nenatoda


5278 8892 38803


1351


14.39
4.78
46.95


0.51


7969
3626 7858
439 3303 323 69


32.59 6.53
24.36 6.58 6.27 1.09 <0.01


3626 20857 3788


762
439 1432 23


32 <0.01


3168
16 773


381 .36
0.43 0.20


69 1176 139
254


15.55
242.92
3.67 <0.01


Nemertinea Sipuncula


46
1277
92 3095
346


14.83 37.58
9.40


1.89 7.06 0.37
1.08


10.37
230.53
2.45 0.08
7.64


25225 339.58 35783 315.65


1524 670
2194


439 1663 162


4.85 3.74 3.06


1.86 3.16 <0.01


4378 166.89


10648


459 851 1316
11
146
60
41


25 36


0.28


23 0.29 21701 184.14


9 16.67
1 13.17 1 20.95 0 1.65
4 2.64
6 2.83
6 0.10
6 0.27
8 <0.01 9 6.48
)0 255.00
2 1.64
)3 0.14 37 1 .91
6 0.07


Annual Average 35257 323.50


U,


Totals 58313 448.65






Table 9. Site l's average quarterly and average annual densities (Number/m2) and standing crops of energy
(kJ/m ) for the major groups of benthic invertebrates.



October January April July Average
Taxa
Density Energy Density Energy Density Energy Density Energy Density Energy


Polychaeta Oligochaeta
Amph i poda Decapoda Tana i dacea


I sopoda Copepoda C uLIacea


Ostracoda
Oph i uro idea Gastropoda Bivalvia


1617
23


128.58 <0.01


23 <0.01 93 0.02


69
2480


Platyhelmi nthes Neme r ti nea Ncma t oda S i puncu I a


46 69


264.95 66.05


5.28 <0.01


Totals 4397 464.91


6629 2125
2240 231 23
2287


693


670
254 1340 46 92 370 208


138.57 0.77
7.99
8.46 0.08 11 .70


7.90


235.53 222.07 25.85
0.20 2.41 <0.01 7.97


5636 345.74 323 5.83
323 6.02
254 0.09
69 0.23
23 1.18
23 <0.01 92 4.33
46 <0.01 46 16.11


785 79.86


46 1.11
624 0.02


17208 669.51 8290 460.54


4735 139 231 69 323 577 23


947 69 1732 1732


46 393 23


31.20 0.03
0.14 2.17 1.09 2.53 <0.01


0.28
20.60 59.81 50.33


1.11 0.01 0.03


11039 164.34


4654 653 699
139 98
722
17
196 272 196
514 1584 12
58
364 58
Annual 10286


161.00 1.66
3.54
2.68 0.35
3.85
<0.01
8.06
0.08
63.06 136.71 55.52
0.05
2.48 0.01
2.00 Average 441.06




Table 10. Site 2's average quarterly and average annual densities (Number/m2) and standing crops of energy
(kJ/M ) for the major groups of benthic invertebrates.


October January April July Average
Taxa
Density Energy Density Energy Density Energy Density Energy Density Energy


Po l ychae ta Oligochacta
Amph i poda Decapoda Tana i dacea I sopoda Copepoda CuIIaCea Mysidacea Ostracoda Hydroida Oph i uro i (lea Gastropoda Bivalvia Platyhe I i thes Nemertinea
Nema toda S i puncu 1 a


ToLal


1963
347 162 23
46


1155 23 23
46


23
3095


139 601 92


38.36
0.50 0.30 0.52
0.16


0.30 0.26 0.30
0.45


5.18
29.98


3.89
0.02 0.26


7738 80.48


5451
1363 2726
46 46
116
416 46


99. 10 1.96
2.54 1.05 0.16 1 .35 0.11 0.53


70 0.60


23 5.56


20626 34.96


46 139
46


1.30 <0.01 5.83


31163 155.06


4158 601 208 23
46 23 69 92


46 23 2541


23
416 393


132.25
2.16 0.10 0.52
0.16 0.27 <0.01
4.33


11.17
5.18 12.30


0.51 0.01
4.85


8662 173.82


7299 739 323 69
139 162 139


162 92
162
416 93


439 23


99.50
9.86 0.50 1.57
0.47 0.47 0.03


471 76 85
4
6 7
44
4


2 4



66



3 1
Ann
144


0.14 22.23 36.29 35.28
0.41


0.01 0.98


10258 207.69


8 92.31 3 3.62
5 0.86
0 0.42
4 0.24
5 0.52
5 0.11
0 1.28
6 0.08
9 0.26
1 0.04
0 9.74
;2 11.66 70 28.12 23 0.10
52 1.43
94 0.01
39 2.98
ual Average 56 154.28




38


The values and authorities cited used to covert standing crops on a dry weight basis to standing crops on an energy basis, for the benthic invertebrate groups common in the impoundments and seagrass beds.


Taxa Conversion Factor Reference Notes
(J/mg dry wt)


Polychaeta Oligochaeta
Amphipoda Decapoda Tanaidacea Isopoda Gastropoda
Bivalvia Platyhelminthes Sipuncula Cumacea
Nemertinea Ophiuroidea Hydroidea Nematoda Ostracoda Mysidacea Copepoda


1
2
3
4
5


Cummins and Wuycheck Day et al. (1973) Thayer et al. (1973) Blaber (1979) Whitfield (1980)


22.72
18.02 15.51
17.43 14.62 14.62 17.81
20.06 22.05 14.19
15.62
20.04 5.71 12.08 18.01 15.62
15.62 14.49



(1971)


Isopod value










average of Oligochaeta and Platyhelminthes





Cumacea value Cumacea value


Table 11.




39


Table 12. Percentage of the average annual standing crop of energy for
major benthic invertebrate groups at each site.




Taxa Ii 12 Si S2


Polychaeta -- 5 37 60
Oligochaeta -- 4 -- 2
Amphipoda -- 6 -- -Decapoda 2 -- -- -Ophiuroidea -- -- 15 6
Gastropoda 36 2 31 8
Bivalvia 57 79 13 18
Sipuncula -- -- -- 2




40


decapods and amphipods in the impoundments and brittle stars and sipunculids in the seagrass beds. Two subgroups, Il-S2 and 12-Si, which departed from the original habitat groups 11-12 and Sl-S2, appeared based on average annual standing crop and on standing crop of molluscs. Site Il had a higher percentage of bivalves than 12, but a lower percentage of gastropods. The same was true for S2 as compared to Sl. Sites 12 and Sl are, therefore, distinctive from their comparison sites Il and S2, respectively, for two reasons. First, they have higher standing crops and secondly they have a higher bivalve to gastropod ratio than their comparison sites.

Comparing the four sites seasonally, the most distinctive feature is that each site appears to operate on a different schedule of maximum and minimum standing crops of energy. Site Il is bimodal with peaks in fall and spring, 12 peaks in fall, Sl in winter, and S2 in the summer. Thus, the impoundments reached their peak standing crops in the fall and spring, while the seagrass beds peaked in winter and summer.

The magnitude of energy storage compartments and total standing crop, of course, are only structural comparisons of the macrobenthos, and do not reflect functional characteristics of the bottom communities. Therefore, significant structural differences found between sites and habitat types do not necessarily reflect differences in the rate of energy transfers within the benthic community.


Epibenthic Invertebrates

The dominant epibenthic invertebrates were caridean shrimp, primarily Hippolyte pleuracanthus, Palaemonetes intermedius, and








Table 13.


Average annual density (Number/m2 ) and standing crop of energy (J/m2) of common large decapods at each site.


Ii 12 S1 S2
Taxa
Density Energy Density Energy Density Energy Density Energy


Caridean shrimp 1.70 1106 8.34 6798 6.99 862 4.06 879


Penaeus sp. <0.01 28 <0.01 65 0.02 631 0.37 2542


Callinectes sapidus 0.01 1230 0.02 861




42


Periclimenes americanus; penaeid shrimp, Penaeus duorarum and Penaeus aztecus; and the blue crab, Callinectes sapidus. Based on Odum (1971), these three groups represent a broad trophic spectrum and therefore should be functionally grouped together for very broad general comparisons, as done here to highlight the fate of net primary production in each system and to compare habitats and community structure. Several other species were collected, but in very low numbers (i.e. the mud crab, Neopanope packardii; the spider crab, Libinia dubia; the hermit crab, Pagurus bonairensis; and the snapping shrimp, Alpheus heterochaelis).

At each site, caridean shrimp were the numerically dominant group (Table 13). However, based on average energy content, blue crab and penaeid shrimp were dominant at sites Sl and S2, respectively. In comparing the yearly totals for each site, Il had distinctively lower standing crops of the major epibenthic invertebrates than the other three sites. Site 12 was dominated by the influence of caridean shrimp, while Sl and S2 had more equitable distributions of standing crops among all three groups.


Fish Community Structure


Species Composition and Seasonality


A total of 44 fish species were found in the study (see Tables

14, 15, 16, and 17). Fourteen species were found in the impoundments, but none was restricted to these sites. Between the two impoundment sites, the difference in the species list is due to rare species. This is also the case when comparing the two seagrass beds; some relatively rare species were unique to one site or the other.










Table 14. Fish collected at site Il.


1978 1979
Species July Aug Sept Oct Nov Dec Jan Feb Mar Apr May June July Aug


Cyprinodon variegatus Fundulus grandis Lucania parva Gambusia affinis Poecilia latipinna Menidia peninsulae
Menidia beryllina Syngnathus scovelli, Microgobius gulosus Trinectes maculatus.


x x x x x x x x x x x x x
x x
x x x x x x x x x
x x x x x x x x x x
x x x x x x
x x x x x x x x x x x x
x x x x x x x x x x


x x
x


x x x x


x
x
x
x
x
x
x


6 6 5 6 4 3 4 5 8 7 8 8 7


x


x x x x


Tota Is 3








Table 15. Fish collected at site 12.


1978 1979
Species July Aug Sept Oct Nov Dec Jan Feb Mar Apr May June July Aug


Anchoa mi tch i i Cyprinodon variegatus
Floridichthys carpio Fundu1l us grand is Fundulus similis Lucania parva Gambusia affinis Poecilia latipinna Menidia peninsulae
Menidia beryllina Syngnathus scovell i Mu(jiI cephalus
Gob iosoma robustunI Microgobius gulosus


x x x x

x x x

x x x x
x x x x
x x x x
x x x x
x x
x x x


x
x x


x
x x x x x x x

x x x x x x


x
x x x x x
x x x x x


x x x
x x
x x
x x x


x
x
x


x
x


x x
x x


x
x


x
x


x x
x x
x x


x
x
x

x


x x x x


x
x x
x x x x x x x x x x x x


6 10 9 10 9 8 9 8 5


Tota Is


7 8 10 9









Table 16. Fish collected at site Si.


1978 1979
Species July Aug Sept Oct Nov Dec Jan Feb Mar Apr May June July Aug


Elops saurus Brevoortia sp. Anchoa mi tchi I i Opsanus tau Hyporhamphus unifasciatus Strongylura notata Strongylura timucu Cyprinodon variegatus Floridichthys carpio Fundulus grandis Fundulus similis Lucania parva Poecilia latipinna Menidia peninsulae Menidia beryllina Hippocampus zosterae


x x x


x


x


x
x x x x
x x x x x x
x x


x x x x x x x x x x x
x


x
x


x


x x


x
x
x


x x x x
x x x x x x x x


x
x x


x
x


x x
x x x x x x x x x
x


x
x


x


x
x


x
x x
x x
x x
x x


x x x x X


x x x


U1


x
x
x
x







Table 16. (Continued)


1978 1979
Species July Aug Sept Oct Nov Dec Jan Feb Mar Apr May June July Aug


Syngnathus louisianae Syngnathus scovell i 01 igopi tes saurus Lutjanus griseus Diapterus auratus Eucinostomus sp. Eucinostomus argenteus Orthopristis chrysoptera Haemulon sciurus Archosargus probatocephalus Lagodon rhomboidesBairdiella chrysoura Cynoscion nebulosus. Leiostomus xanthurus Mugil cephalus Chasmodes saburrae Gobiosoma robustum Microgobius gulosus


x


x x x x x x
x


x x x x x x x x


x x


x


x x


x


x


x


x


x x
x x x


x
x
x


x x x
x x x
x


x

x
x


x


x
x


x


x
x


x x
x x x


x
x


x
x


x

x


x x x


x

x
x


x x
x x


x


x x


x
x

x

x
x
x

x
x


x x x
x x


x
x
x
x
x


x

x
x


x
x


x x
x x








Table 16. (Continued)


1978 1979
Species July Aug Sept Oct Nov Dec Jan Feb Mar Apr May June July Aug


Paralichthys albigutta X
Paral ichthys lethostigma X
Achirus lineatus X X X
Trinectes maculatus X X X


Totals 6 8 12 9 17 17 12 19 18 16 14 19 16 19










Table 17. Fish collected at site S2.


1978 1979
Species July Aug Sept Oct Nov Dec Jan Feb Mar Apr May June July Aug


Brevoortia sp. Anchoa mitchilli Opsanus tau Hyporhamphus unifasciatus Strongylura marina. Strongylura notata Strongylura timucu. Cyprinodon variegatus Floridichthys carpio Fundulus grandis Fundulus similis Lucania parva Gambusia affinis Poecilia latipinna Menidia peninsulae Menidia beryllina


x


x


x


x


x


x


x x x


x x


x x


x x


x x


x


x
x


x


x
x x


x
x


x
x


x x


x
x x x x x x x


x


x
x x x x
x x
x
x x x x


x


x
x x x


x
x x x


x
x
x


x
x x x x


x
x


x x


x
x
x
x


x
x


x
x x


x
x


x
x







Table 17. (Continued)


1978 1979
Species July Aug Sept Oct Nov Dec Jan Feb Mar Apr May June July Aug


Hippocampus erectus Hippocampus zosterae Syngnathus louisianae Syngnathus scovell i Oliqoplites saurus Trachinotus falcatus Lutjanus griseus Lutjanus synagris Eucinostomus sp. Eucinostomus argenteus Eucinostomnus gula Haemulon sciurus Archosargus probatocephalus Lagodon rhomboidesBairdiella chrysoura Cynoscion nebulosus Leiostomus xanthurus Chaetodipterus faber


x


x


x


x x x x x x x x . x


x


x
x


x x
x


x x x x


x
x


x x
x


x
x


x x x
x x


x
x


x
x


x
x
x
x
x
x


x x


x


x


x


x
x

x
x


X x
x


x


x x x x

x x x x
x


x
x x x


x


x
x


x


x


x

x
x
x


x
x
x
x







Table 17. (Continued)


1978 1979
Species July Aug Sept Oct Nov Dec Jan Feb Mar Apr May June July Aug


Mugil cephalus Gobiosoma robustum Micropobitus gulosus Paralichthys albigutta Para. ichthys lethostigma Achirus lineatus Trinectes maculatus Spheroides nephelus Ch i lomycterus schoepfi


x


x
x


x x


x


x x x x x x x x x x x x
x x x x x x x x x x x x


x x


x


x


x


x


x


x
x
x


x


x


x


14 13 16 11 14 17 18 16 20 18


Q,


To taIs


15 9 11 19




51


The impoundments were characterized by high densities of several species of atheriniform fishes, as well as the clown goby, Microgobius gulosus, all of which were considered yearly residents. Site Il showed a slight decrease in total species number during the winter which was quickly made up in the spring, beginning in April. Site 12 did not experience a winter exodus, as did Il. Three of the four seasonally occurring species at 12 were found between October and January. The only commercial or sport fish collected was a solitary Mugil cephalus at site 12 in April.

The yearly residents of the seagrass beds included the atheriniforms and the goby of the impoundments, plus the gulf pipefish, Syngnathus scovelli, and the code goby, Gobiosoma robustum. Juveniles of species of the families Sciaenidae, Gerreidae, and Sparidae were also dominant community members on a more seasonal basis.

The seasonality of both density and energetic standing crop

(Tables 18 and 19) at the seagrass sites Sl and S2 and the impoundment site 12 appeared to be on a regular cycle of winter minima and summer maxima. Site Il, in contrast, had three depressions in both density and energetic standing crop, October, March, and June.

The average densities and standing crops of energy at the impounded marsh sites were significantly higher (Student's t, p < 0.05) than at the seagrass sites. Differences between the two impoundments and differences between the two seagrass beds were not significant.

The sheepshead minnow, Cyprinodon variegatus, was by far the dominant member of the impoundment communities studied in terms of average density and average standing crop of energy (Table 20). The same atheriniform fish are shared dominants between sites Il and 12,




52


Table 18. Total fish densities at each site.


Density (#/m2)
Year & Month
Il 12 Si S2


1978 July 22.70 ---- 5.29 3.37
August 12.59 24.09 0.63 3.76
September 31.56 10.89 2.28 4.57
October 6.10 9.16 2.26 4.00
November 11.48 8.73 1.14 3.98
December 13.61 3.28 0.84 0.90
1979 January 11.23 3.34 2.42 1.64
Februrary 17.65 11.11 2.32 6.81
March 4.36 18.85 1.19 1.06
April 16.20 17.76 1.07 0.82
May 14.25 38.13 2.91 2.00
June 7.09 57.49 4.14 9.40
July 14.88 52.36 10.60 7.94
August 47.19 101.66 13.62 7.32


3.62 7.32


Mea n


27.45




53


Table 19. Fish standing crops of energy (joules/m2) at each site.



Year & Month I 12 Si S2


1978 July 41019 ---- 17737 9735
August 10147 50072 7642 25949
September 111200 33635 5577 15993
October 8083 49056 8608 9875
November 9318 8846 1093 7933
December 9737 1524 2728 2584
1979 January 19717 5816 4768 6654
Februrary 32538 28034 3746 2996
March 5791 35349 1452 1960
April 133374 31117 2033 1559
May 81034 52791 3614 4156
June 42413 99887 6374 9739
July 87057 103806 14132 9273
August 159985 194279 11637 9713


Mean (all months) 53672 53401 6510 8437


Mean(Sept 78-Aug 79)


58354 53678


5480 6870








Table 20.


Percentage of average annual density and standing crop of energy for the major fish species at each site; * = present, but less than 0.2% of average density or less than 0.5% of average standing crop of energy.


Percentage of Average Density Percentage of Average
Standing Crop of Energy
Species
Ii 12 Si S2 Ii 12 Si S2

Cyprinodon variegatus 80.0 4.6 --- --- 87.0 6.7 --- --Poecilia latipinna 7.4 7.5 ---* 5.9 10.6 *
Gambusia affinis 4.2 33.6 ---* 0.6 12.7 *
Fundulus grandis 0.02 0.5 --- ---* 6.5 --- --Menidia beryllina 2.3 0.6 ---* 3.7 1.1 ---*
Menidia peninsulae 2.2 14.9 14.6 20.8 1.5 21.9 33.1 33.8
Lucania parva 3.6 36.1 59.7 58.9 1.3 38.7 27.1 24.3
Microgobius gulosus 0.3 0.6 6.3 4.0 * 1.0 4.9 *
Gobiosoma robustum ---* 7.3 3.5 ---* 4.1 *
Syngnathus scovelli * 0.4 5.0 6.9 * * * 5.0
Lagodon rhomboides --- 0.2 0.4 --- --- 11.5 12.0
Bairdiella chrytoura --- --- 1.5 1.4 --- --- 4.7 9.3





55


but 12 has a much more equitable distribution of standing crops of individuals and energy. The two most abundant species across all habitats were the rainwater killifish, Lucania parva, and the silverside, [lenidia peninsulae. Within the seagrass beds, the two gobies and the pipefish made up a large fraction of the average number of individuals per month, but, in terms of standing crops of energy, the more seasonal pinfish, Lagodon rhomboides, and silver perch,

Bairdiella chrysoura, weremuch more significant.


Environmental Correlations


The correlations (Spearman Rank) of numbers of fish species, fish density, and fish standing crops of energy to salinity, median water temperature, and standing crops of seagrass (Sl and S2 only) are given in Table 21. The strongest correlations existed between fish standing crops in units of energy and median water temperature, especially at sites 12 and S2.

Correlations of community structure to salinity show a contrasting pattern between the two impoundments. The number of fish species found each month at the low salinity site (Il) was positively correlated with salinity. Site 12 had much higher average salinities and the number of fish species found each month was negatively correlated with salinity. Standing crop of energy, however, had a significant (a = 0.05) positive correlation to salinity at 12, while almost no correlation existed between them at site Il. The seagrass beds had no significant correlations between fish community structure and salinity.

Sites Sl and S2 showed contrasting correlations between fish community structure and seagrass standing crop. Site S2 had significant







Table 21. Correlations (Spearman Rank) of structural characteristics of the fish communities at each site
with monthly salinity, median water temperature and seagrass density (Si and S2 only); r
correlation coefficient; Prob > Irs With an H of rs = 0; *--significant at p < 0.05,
**--significant at p < 0.01; N = 1 .



Site Structural Salinity Median Water Seagrass
Characteristic Temperature Density

r Prob > |r s r Prob > Irs1 rs Prob > Irs

Number of Fish Species 0.53 0.063 0.65 0.014 *
i Fish Density -0.02 0.950 0.40 0.178
Fish Standing Crop-Energy 0.07 0.830 0.52 0.066


Number of Fish Species -0.40 0.172 -0.48 0.095
12 Fish Density 0.32 0.292 0.70 0.008
Fish Standing Crop-Energy 0.58 0.038 0.83 0.001 *


Number of Fish Species 0.36 0.220 0.32 0.282 0.11 0.724
Si Fish Density -0.33 0.272 0.33 0.268 0.04 0.887
Fish Standing Crop-Energy 0.27 0.370 0.59 0.033 0.24 0.426


Number of Fish Species 0.20 0.502 0.49 0.090 0.68 0.011
S2 Fish Density 0.15 0.626 0.68 0.011 0.45 0.128
Fish Standing Crop-Energy 0.32 0.294 0.72 0.006 0.68 0.011 *




57


(a = 0.05) positive correlations of species number and standing crop of energy to seagrass standing crop. The correlation of fish density to seagrass was also highly positive, though not significant, at S2. In contrast, site Sl had very weak positive correlations for all three structural characteristics to seagrass standing crop. Energy Contents


The energy contents of juvenile and adult age classes (Table 22) are significantly site specific (Duncan's Multiple Range Test--"DMRT," a = 0.05). Rather than a continuous gradient of energy content values between the sites, all the sites had significantly different energy contents for juveniles, resulting in a discontinuous gradient of communities. The only overlap of communities was found between the adult fishes in the seagrass beds. The juvenile and adult age~classes of the impoundments were not significantly different from each other (DMRT, a = 0.05), but in both cases, as shown in Table 22, were higher in energy content than similar age classes from the seagrass beds. Site Sl was the only site where the two age classes were significantly different in energy content (DI'RT, a = 0.05); in that case the average adult had a higher energy content per mg ash-free dry weight than did the average juvenile.

The differences in mean energy content for species at each site are presented in Table 23. Of the two dominants, Menidia peninsulae and Lucania parva, Lucania demonstrated a significantly greater energy content per gram of ash-free dry weight at sites Il, 12, and S2 (DMRT, a = 0.05). The two seasonal dominants in the grassbeds, Lagodon rhomboides and Bairdiella chrysoura, are also significantly





58


Table 22. Mean energy content of juveniles and adults of all species
at each site; means which are not significantly different
from each other are connected by a horizontal bar, Duncan's
Multiple Range Test, a = 0.05.


Juveniles


N


113


84


111


79


N
J/mg ash-free dry wt Si-te


23.646 23.953 24.743 25.124


S1


77


S2 82


12


154


Ii


101


24.086 24.117 24.488 25.299


S2 S 2


J/mg ash-free dry wt Site


Adults


I2 - Il




59


Table 23a.


Mean energy content of common species at site Il; means which are not significantly different from each other are connected by a vertical bar, Duncan's Multiple Range Test, a = 0.05, N--sample size.


Species Energy Content N
(J/mg ash-free dry wt)


Lucania parva 25.655 8
Gambusia affinis 25.472 3
Cyprinodon variegatus 25.808 117
Poecilia latipinna 25.052 18
Menidia beryllina 24.839 25
Menidia peninsulae 24.820 20





60


Table 23b. Mean energy content of common species at site 12; means
which are not significantly different from each other are connected by a vertical bar, Duncan's Multiple Range Test,
a = 0.05, N--sample size.



Species Energy Content N
(J/mg ash-free dry wt)


Anchoa mitchilli 25.840 4
Gambusia affinis 25.309 49
Lucania parva 25.122 51
Poecilia latipinna 24.804 29
Microgobius gulosus 24.375 11
Menidia beryllina 24.247 15
Cyprinodon variegatus 24.203 42
Fundulus grandis 23.852 30
Menidia peninsulae 23.769 39




61


Table 23c. Mean energy content of common species at site SI; means
which are not significantly different from each other are connected by a vertical bar, Duncan's Multiple Range Test,
a = 0.05, N--sample size.



Species Energy Content N
(J/mg ash-free dry wt)


Cyprinodon variegatus 25.531 2
Lagodon rhomboides 24.908 20
Haemulon sciurus 24.277 8
Microgobius gulosus 24.245 18
Gobiosoma robustum 24.221 7
Syngnathus scovelli 23.891 15
Anchoa mitchilli 23.787 5
Leiostomus xanthurus 23.763 3
Eucinostomus (juveniles) 23.756 6
Lucania parva 23.683 36
Oligoplites saurus 23.623 3
Menidia peninsulae 23.598 47
Cynoscion nebulosus 23.303 4
Menidia (juveniles) 23.078 5
Bairdiella chrysoura 22.878 12
Mugil cephalus 22.877 1




62


Table 23d.


Mean energy content of common species at site S2; means which are not significantly different from each other are connected by a vertical bar, Duncan's Multiple Range Test, a = 0.05, N--sample size.


Species Energy Content N
(J/mg ash-free dry wt)


Lucania parva 24.953 53
Lagodon rhomboides 24.758 17
Fundulus grandis 24.539 3
Cyprinodon variegatus 24.249 4
Archosargus probatocephalus 24.173 3
Microgobius gulosus 23.879 9
Menidia peninsulae 23.802 37
Syngnathus scovelli 23.705 21
Floridichthys carpio 23.643 2
Bairdiella chrysoura 23.326 12
Paralichthys albigutta 22.667 3




63


(DMRT, a = 0.05) different in their average energy content per gram of ash-free dry weight in the two grassbeds. Within the impoundments and S2, Cyprinodon variegatus drops to significantly lower energy content per gram of ash-free dry weight than Gambusia affinis and Lucania parva. Also, at 12 the species with higher energy contents appear as more discrete groups than in I] and S2 and, to some degree, Sl.


Fish Community Function

Monthly respiration and production for the major fish species in each community are shown in Tables 24, 25, 26, and 27. Respiration was approximately one order of magnitude greater in the impounded marsh sites (Il and 12) than in the seagrass sites (Sl and S2). Differences in annual production were even more dramatic, with the impoundments (Il and 12) roughly 22 and 15 times more productive, respectively, than the seagrass beds.

The impoundment sites were most productive during the months of April and June, whereas the first large pulses of production occurred in the seagrass beds during June and July. All four sites experienced large respiratory losses during July and August. A second staggered seasonal pulse of production was noticeable in the fall, with Il peaking in September, 12 and Sl delayed until October, and S2 with approximately 39% of its total production occurring during October and November. The bimodal production process of fishes in the seagrass beds is consistent with earlier studies on the shallow water fish communities of the northern Indian River (Schooley 1977) showing a spring/fall recruitment sequence for the shallow seagrass bed communities.









Table 24. Site Il respiration and positive production values in J/m 2; R-respiration,
P-production, %-percentage of the site's annual total for respiration and
production contributed by each species.


Sept 18 Oct Nov Dec Jan 79 Feb March April May June July Aug 79 Totals %


R 57667 55102 SIll 6010 5295 9957 7122 26598 71677
CvpgrInolon varieqatus
P 80038 8180 3659 129069

R 89 61 37 33 5 3 2 96 424
CGambusla affinis
P 16 38 2

R 15 10 3 2 3 9 56 211


Lucanila vr Fundulu grandis Men ida bery ina


4


R 1723
Menidia peninsulae
P 561

R 117
MicroobIus g loss
P 39

R 60
PoecIi ia lat ipinna
P 6


192 1207 1388

58 1255 1292 965 177

284 125


205 169

21


40


274

578 185 396


258 438

382

171 155


193 24

151


Synonathus scove lii
P


1392 4516

2182 27494

1319 1207



26 65



344 1373



3 35

106


144


A 5981S 36883 7516 7634 5759 10422 7726 29834 79508

P 80660 169 53S 1380 9154 3661 387 131291 27600


47625 52965 166049 431228 84.2 23942 858 245746 87.3

399 456 4888 6493 1.3

220 276 0.1

613 3697 6049 10668 2.1

496 545 0.2

48 261 219 528 0.1

249 249 0.1

3389 521 1251 14826 2.9

31949 11.4

131 132 45 7502 1.5

62 1428 0.5

197 422 414 1663 0.3

1II 470 0.2

3682 5623 27952 39055 7.6

575 112 695 0.2

14 52 0.01

106 0.04

3 147 0.02


56098 64077 146870 512142 25233 1281 111 281462


Spec Ie%


Others



, t.)I














Table 25. Site 12 respiration and positive production values in J/m2; R-respiration,

P-production, %-percentage of the site's annual total for respiration and
production contributed by each species.



Spe-cies Selp 18 Oct Nov Dec Jan 19 Feb Malch April May June July Aug 19 Totals %


Cypr inodon var iegatus
P

R undi us grandis
P

R a bsa aff inis
P

R lida .3(parva
P

R Menidid peninsul e
P

R Menidia beryllina
P

R Men idia sp.
P

R Mit Ig1bias 10lsS
P

R Poec i Iia I a tipi ...a
P


R Ynqna In, Scove I I i
P

. R


3


6006 3145 812 174 15 422 2259 3599 1204 1577 11476 12067 42756

419 514 834 1089 2483 5339

48i9 10538 1956 102 2078 3140 1288 1263 2285 731 28200

4138 12734 5)06 156 22634

3634 1532 1851 1777 310 535 932 2370 8429 16560 24033 40583 102546

321 1486 160 176 460 1823 2117 6343

2378 1227 1027 275 169 1171 5221 18545 21533 34597 47526 105736 239405

317 179 519 2270 22269 11550 7717 10818 55639

0853 19681 927/ 411 203 2178 3255 16510 9230 30678 29496 45 151817

6799 5128 4627 5363 1243 63000 86160

194 217 19 136 512 328 61 1039 1856 474 4836

21 329 61 411

549 549

241 241

838 269 298 116 84 165 32/ 999 948 433 338 44 4859

210 215 36o 3/5 1241 149 2500

5128 4066 1228 404 59 192 625 820 6516 14155 21429 22693 77315

1666 318 34 3 96)0 11957

27 123 72 314 21 83 228 W24 712 467 30 2328

40 q I I5 236

4/ 74 1 72


6.5

2.8 4.3 11.8

15.7

3.4 36.5 29.0 23.2

44.9 0.7

0.2

0.1 0.1 0.7

1. 3 11.8

6.2 0.14 0.1

0.01


0I m-


9)O


90 0.05












Table 25. (Extended)


R GobIosonia robustum
P


R 53683 40810 16779 3259 1023

P 11956 20376 6134 305 379


5361 15125 '.7,403 49860 100169 1381.69 182373 655220 7690 5475 298146 115 74706 21772 12996 191750


35 41


Totals


172 287


78 0.01



1459 0.1


C-I


AnsrhS_4_ m ltchl) I_ _













Table 26. Site Si respiration and positive production values in J/mn2; R-respiration,

P-production, %-percentage of the site's annual total for respiration and
production contributed by each species.



SpecIes Sept 78 Oct Nov Dec Jan 79 Feb March April May June July Auq /9 Totals %


Anchoa ,I tchl II
P

R
3.6irdiella hrysu. a
P

R
CY11SiOn nebulusus
P


Hlan.u Ium sc i rus


LaJ"'I" Iho"boi des Leiost .Us ,anthurus Lm ania parv Menidia peninsul.,e Hicrlo 35 9tt Is us SynmnathIs scove I I


R 164 326 88


203 247 260 104

408


R 234


R 1575 744 276

P 1160 906

R 158

P


R 2253 1843 895 201


24


P 61 17

9 1612 746 456 91 332

P 658 309

R 10 is 56 114 245

P 9 73 118 254

R 185 171 215 192 180

P 202 101


19 186 1 31

296


25 7 946 1.6

30 326 2.5

373 2424 1395 4395 7.3

1945 257 2202 17.0

15 33 124 783 1.3

78 486 3.8

21 23 495 773 1.3


522 581 3698 6.1

2066 16.0

16 15 50 64 303 0.5

111 111 0 .9

30 8 764 3707 8083 10598 28406 47.2

36 89 203 1.6

592 396 153 1233 1159 1313 3026 11109 18.5

372 7 2704 393 4448 34.3

562 420 434 583 350 56 65 2860 4.8

254 96 275 68 1147 8.9

231 105 105 121 305 426 564 2812 4.7

59 33 19 414 3.2


16


10 - 9


12 3 31


44 0.0/

154 1.2


Eucinostomws 1,













Table 26. (Extended)


R

p


R


HtPRocampus sp. Brevoortla sp. rohiosoma robustum


8 12


25

4 55 196

1,)8

11 46 107 322 388 503 630

is 63 152 60 201 37'


25 o.04

25 0.2

109 364 0 6

198 i .s

418 3','4 4 3114 5

865 6 ;


R 38 34 237 141 4 4 11 93 562

P 164 124 2 19 309

R 6641 4156 2136 897 1036 1718 1380 1489 3672 61,82 132142 17282 60194

P 1169 2197 88 876 435 668 528 812 591 2807 2340 443 12951.


nth1rs rota I


0.9

2.4


C)
00














Site S2 respiration and positive production values in J/m2; R-respiration, P-production, %-percentage of the site's annual total for respiration and production contributed by each species.


Sept 78 Oct Nov Dec Jan 79 Feb March April


May June July Aug 79


R 28


Anchoa mi tchIlli Rairdlella chrysoura



Cytioscion nebulosus Eticlnostonvus sp. Gbhiosoma robustum Lagodon r ho,,bo ides











Mi-Cril pi siiu I
M~~~~~~ irjoi tlsi


p

R 7181 284

P 36

R 166 35


P

R 16

P 13

Rt 57

P 73

R 2098


17 4 5

13


109 160

377

718 195


R 3139 2401

P 897

R 10149 46583


it,

117 I fir


21495

776

2601


R1 16;9

2 8 v


200

19


1020 210


p



P
Rt


I 32 14


21


2


92 178 1 31

65


199 76


759 ,91 1IS 36

51,


93

10


114 3 91


72 18 321 934

1,nA


1053 1 31



60


517 707

670

739 187

I1811


505 91A I


87 0.1

21 0.7

447 2249 1830 6991 8.6

1729 426 2IV)l 16.8

202 0.2


20 587 651

13 39

276 187 57 1583

81 723

32 144 2 2689



63'? 74116 6551, 30981

107 155 2567

590 14712 4082 27882

37 3 4 7289

7" I R 4 6 3058

2. 3S99)

71 is 380


0.8 0.3 1.9 5.5 3. 3



38.0 19.7

34. 2 1 7.5

3.8 77.6 0. S


Opsaus tau


23 0 01

9 0.1


I


Table 27.


Species


Totak a


Powc-il ia la t ip i n











Table 27. (Extended)



R 394
Syngnathus scovel i Menidfa beryllina


Achirus Ifneatus FIorldichthys carpio


125 70


258 246 83

214 68


56


97 142 144 1 354 1666 65;

90 310 744 11 1


14 18


27 30



12 13


R


45 52


5220 6.4

1609 12. 3

32 0.04



154 0.2


23 24 72 0.1


P


R 297 2 156 9" 114 125 187 327 86 47 1435 1.8
OthPrs 6 6 0.05


R 19124 8023 5884 2543 1013 1621 1202 1159 2915 10221 131,46 13959 81 41,0

p 248 962 4226 242 1265 191 660 630 807 804 2234 694 13053


-4




71


Annual production and respiration within site Il was dominated by Cyprinodon variegatus. The next two dominant species are possibly more noteworthy for their ratio of production to respiration than the absolute quantity of either. Menidia beryllina contributed a disproportionately higher share of production to total community production for its average standing crop and respiratory demands, while the Poecilia latipinna population produced very little net production relative to its large metabolic losses within the system.

At site 12, the impoundment canal, production and respiratory losses were more equitably distributed among six species than they were at Il. The two dominant species were Lucania parva and Menidia peninsulae. The Lucania parva population had a large portion of its annual production in August, as did the Gambusia affinis population. Respectively, they produced 44% and 40% of their yearly population productions during the warm month of August at site 12.

Lucania parva is also a functionally dominant species in the

seagrass beds. However, the population's contribution to annual production appears less significant and, at Sl, was a minor part of total community production. Two species that were important in their contributions to production within the seagrass beds were Bairdiella chrysoura and Microgobius qulosus. The former was a seasonal recruit from June through September, while the latter was a continual resident of both seagrass beds. The same type of disproportionality in rates of production and respiration found for two populations at site I] was also found within the seagrass beds. However, in this case it is intraspecific for the species Menidia peninsulae, a dominant functional member of both seagrass beds. Menidia peninsulae made noticeably




72

different contributions to the annual production and respiratory balance within each community. At site Sl the population's ratio of production to respiration is 0.4, while at site S2 the same ratio is

0.08.













DISCUSSION


Abiotic Factors

The controlling physical factor within the systems studied is the

variation in solar radiation. This variation produces a dynamic balance among the influences of direct solar heating, evaporation, and precipitation in generating the daily physical-chemical characteristics of the aquatic habitats studied. During the winter, temperature depression is correlated with reductions in the structure and function of the fish communities.

In the seagrass beds Jones et al. (1975) suggested a two season pattern for the resident fishes. During the warm/wet season they hypothesized an inverse relationship between rainfall, which led to lower salinities, and the number of species occupying the seagrass beds. The second response hypothesized was that during the cold/dry season, even though rainfall was decreasing and salinity rising, the drop in water temperature resulted in a further decline in the number of fish species. Schooley (1977) demonstrated a bimodality in density and diversity in the shallow water habitats of the northern Indian River and Mosquito Lagoon. Because of their shallowness, these habitats may reach zones of appreciable thermal stress during midsummer and midwinter, affecting both residents and seasonal recruits. Both seagrass beds had slight late-summer depressions in density followed by higher levels in the fall.


73




74


Within the impoundment 12 the correlations of both salinity and

temperature to fish community structural characteristics are unclear

due to the influence of marsh morphology. Small changes in water level can have vast surface area effects within the impounded marshes (Snelson 1976). With heavy rainfall, the total marsh area may increase dramatically during the cooler months, as it did at 12 during January. Therefore, subsequent density measurements are lowered as a function of the proximity of newly covered marsh for dispersal of the standing crop. Similarly, during the warmer dry months densities would increase as water evaporated from these shallows. This could lead to a positive correlation of standing crop to salinity. This theory may explain the correlations at 12, but density was not significantly (a = 0.05) correlated with mid-channel depth at this site. The significance of this shift in ecological density at 12 remains.to be investigated. Similar phenomena are not believed significant at

the other three sites.

Day et al. (1973) found temporal patterns within a Louisiana salt marsh and shallow estuarine system to be controlled by temperature, as did Adams (1976a) in a North Carolina Zostera bed. Subrahmanyam and

Drake (1975) found no correlation of abundance (numerical or biomass) with seasonal temperatures or salinities in two north Florida salt marshes. However, several species groups did show significant correlations to either temperature or salinity.

The seasonal succession in the recruitment of the juveniles of

several species found in earlier studies of seagrass beds (Jones et al. 1975, Schooley 1977) was also observed. This same sort of recruitment sequence, which would be expected for a marsh (Subrahmanyam and Drake




75


1975), did not, of course, occur within these impounded marshes. Some minor recruitment may occur at water pumping stations (Jack Salmela, personal communication) when water levels are being maintained in the impoundments by the pumping of water in from the open lagoon.

Snelson (1976) concluded that the major factors controlling the spatial distribution of fishes in permanent impoundments were salinity and vegetative cover. Both salinity and vegetative cover differed between the two impoundment sites studies; however, salinity differences between Il and 12 would not appear to be physiologically significant to the dominant atheriniform fishes. Snelson (1976) and Gilmore (1977) both characterized the impoundments of the Indian River area as stressed environments to which only a small group of species are adapted. During the period of this study the two impoundment sites did not appear any more "stressed" in terms of fluctuations of salinity or temperature than did the shallow seagrass beds. The obvious difference is the open versus closed nature of the two systems. Species within the impoundments do not have a temperature and/or salinity refugium to which they can retreat when conditions become too stressful for that particular species. It appears, then, that knowledge concerning

factors other than environmental fluctuations, such as the degree of potential recruitment and the flushing of detritus, may also be important to our understanding of the differences between marsh and seagrass fish communities.

Gilmore (1977) listed 26 species that have been found in the

impoundments of the Indian River system. All of them were also found in the open estuary. Snelson (1976) found that brackish impoundments of Merritt Island support about ten species, the dominant six in all





76


cases being the same that dominated sites Il and 12. In the grass flats of the Indian River, a total of 208 fish species have been collected (Gilmore 1977), 87% of which are found primarily as juveniles. Approximately 30% of species collected in seagrass beds Sl and S2 were found only as juveniles, and another 21% were found predominantly as juveniles.

The dominant species collected in this study were different than

those found to be the dominant grass flat species by Jones et al. (1975). Jones et al. (1975), using a large sweep seine (61 m) to cover an area of 1,161 m2, described the residents of the grassbeds in the southern portion of the Indian River as being dominated by Eucinostomus gula, Eucinostomus argenteus, Diapterus auratus, Lagodon rhomboides, and Bairdiella chrysoura. The species found to structurally and functionally dominate the seagrass beds in this study were smaller demersal and bottom dwelling forms. The sampling techniques used in this study are biased towards these species, just as the technique used by Jones et al. (1975) was biased against these same species (Gilmore et al. 1976). The techniques used here are assumed to be biased, as are all fish collecting techniques, but are believed to realistically reflect fish standing crops of density and energy within the seagrass beds

(Gilmore et al. 1976).


Biotic Factors

The most important biotic factor controlling communities within Indian River seagrass beds is seasonal change in macrophyte standing crop. During the spring and early summer, the grass beds provide greater habitat complexity and strongly influence the physical,




77


chemical, and biological processes of the entire system. In the fall the grass beds, often carpeted with diatoms, die back, producing vast amounts of detritus that show up about six weeks later with a resulting pulse of organic carbon into the sediment (Clark 1975). This seasonal pulse effect appears to be a general characteristic of seagrass-based ecosystems (Phillips 1960, Odum 1967, and Phillips 1974). Clark (1975) discussed the effects of this seasonality of detrital input on the dominant groups of benthic invertebrates within the lagoon. The density of invertebrates in both seagrass beds, Sl and S2, was greatest in January, followed by July, April, and October, in that order. In Clark's (1975) study of the benthic invertebrate communities of seagrass beds, he found two peaks in density, the maximum peak being in November-December with a second in May. The seagrass beds studied here appear to operate under the same seasonal density patterns as those studied by Clark (1975). The seasonality of detritivores has an overwhelming influence on total benthic invertebrate density in the grass beds of the northern Indian River (Clark 1975). Clark (1975) pointed out that the early winter peak in density is a direct response to that growing-season's decomposing seagrass, while the early summer peak may be a response to increased availability of refractory detritus, which was not decomposable at lower winter temperatures. However, he also pointed out that the reproduction of temperate species is keyed to increasing vernal temperatures and is a factor contributing to the early summer peak in density as well. This sequence of density cycling which is keyed to detrital input and reactivation appears to dynamically link the benthic invertebrate community with the production and seasonal recruitment of fishes within the seagrass beds.




78


Within the impoundments the pulsing, if any, of detrital input is not known. Pool et al. (1974) reported a general pattern of increased leaf fall during the rainy season for mangrove forests in south Florida. If this is true for the impoundment mangroves of the Mosquito Lagoon area, maximum leaf fall, on the average, would occur during June, July, and August. The maximum standing crops of Chara occurred in December and September at sites Il and 12, respectively. Based on this limited information, it is speculated that the two primary detrital sources are pulsed, but not synchronously. rIangrove litter is assumed to produce a late summer pulse in finer detrital particles; winter diebacks of Chara, on the other hand, would produce a spring pulse in utilizable organic material as temperature increases speed up bacterial and meiofaunal detrital processing. The seasonality of invertebrate infaunal densities at site 12 appears to correlate with such a model of detrital pulses, since densities in fall and spring are greater than in winter and summer. This is the reverse of what was observed for density in the seagrass beds. The same pattern found for density and energetic standing crop at 12 was also found for standing crop at Il. The density at 12 during the fall was less than that found during the winter. The greater than average rainfall during December may have produced greater litter production during this time. If isopod populations tracked this hypothesized pulse in detritus by increased reproduction, it would explain their numerical dominance and relatively smaller contribution to energy standing crop per individual due to a predominance of juveniles and immature individuals.

The amount of detritus produced in the impoundments appears to be greater than in the seagrass beds. Unfortunately, with complete data




79


from only one impoundment, the significance of the difference found is not known. Chara, which was found in dense patches in various portions

of the impoundments only contributed 20% of estimated net production.

The production estimate for the impoundment mangroves of site I

(0.47 g-m-2 -d l) is approximately of the same level as those found

for mangrove scrub forests at Turkey Point in southeast Flor-ida (Pool et al. 1974). This forest is then about 25% as productive as basin forests of southern Florida, which have greater freshwater turnover than scrub mangrove forests.

Annual net production in the seagrass beds averaged 3,060
-2 -lI
kJ-m2 y for sites Sl and S2. By comparison, using Eiseman et al.'s (1976) estimate of above ground monthly standing crop and applying the same calculations and conversions, an average of 3,065 k-m2.y1 was derived. Clark's (1975) estimate of monthly standing crop for. northern Indian River seagrass beds applied to this same formula yielded an estimated average annual net production of only 1,273 kJ-m-2.y-1. Red and brown algae, which were not significant in the shallow grassbeds at Sl and S2, did contribute to production in the deeper sites studied by Clark (1975) and Eiseman et al. (1976). Maximum minus minimum standing crop was used as an estimate of net production of algae (Steve Davis, personal communication). Net production was converted to joules based on average calorimetry values for phaeophytes and rhodophytes of 12.79 and 13.27 J/mg dry wt, respectively (Cummins and Wuycheck 1971). This would add 279 kJ-m- 2y-I due to red algae production to the 1,273 J-m- y produced by seagrass in the area studied by Clark (1975). Red algae are estimated to produce 783 kJ-m- .Y-1 and brown algae 224 kJ-m-2 Y-I for a total of 1,007 kJ-m -2 -I in the




80


grassbeds studied by Eiseman et al. (1976). In these two cases, estimates of net seagrass production were 3 to 4.5 times that estimated

for large algae.

The seagrass beds of this system are on the lower end of the range of annual production for seagrass-based ecosystems. Assuming 1 gC is equivalent to 42 kJ, production estimates in kJ-m-2.y-1 for Zostera beds were 8,943 and 5,280 in North Carolina (Adams 1976b), 24,528 in Puget Sound (Phillips 1974), and, for a Thalassia bed in the Caribbean, up to 122,640 (Thayer et al. 1975b).

Production in both the impoundments and the seagrass beds is very low relative to similar systems. The reduced circulation in mangrove impoundments such as Il is believed to be partially responsible for lowered mangrove production. The frequency and duration of winter freezes may also be a significant factor. Within the seagrass beds Clark (1975) speculated on four nonexclusive hypotheses for reduced production within the grass beds of the Mosquito Lagoon and northern Indian River. They were

1. lack of appreciable currents, leading to localized depletion of nutrients;

2. nutrient limitation due to sediment characteristics (i.e.

coarse sediments with less surface area for microbial

regeneration of nutrients);

3. intolerance to low temperatures for seagrasses at the

northern extent of their range; and

4. carbonate limitation.

The characteristics of the entire ecosystem and specifically the fish communities are possibly then controlled by these same processes.




81


Production

Total production in each system was the sum of the positive production values for each species each month. Negative production values were excluded for the summation of total production, which according to Chapman (1978) should be done if one is interested in community metabolism and estimating assimilation and production efficiencies between trophic levels. The most noticeable portion of production not taken directly into account by these calculations is production in the form of reproductive products. This is assumed to have a greater potential impact on underestimating the production at sites I and 12 which had a larger percentage of year-round residents than did the seagrass beds. The impact of this omission in the overall production estimates is not known.

Total fish production within the seagrass beds was very similar, 12.95 and 13.05 kJ-m-2.y-1. The impoundments had much higher production levels, 281.46 and 191.75 kJ-m-2.y-1. The seagrass bed, though similar in overall production levels, were rather dissimilar in the relative contribution to site production by year round residents of the grassbed and seasonal recruits, which were predominantly juveniles. At site Sl the seasonal recruits produced 42% of the yearly total production, whereas at S2 they only contributed 17%. The diurnal resident Anchoa mitchilli accounted for 3% of the yearly production at site Sl while at S2 it contributed approximately 0.1%.

There are few comparative studies of finfish production in marine systems. Clarke (1946), based on commercial landings for George's Banks, estimated a harvest production of 0.15-0.73 g dry wt-m-2 y-1




82


He estimated net production as possibly twice this, or 0.30-2.46 g dry wt-m .y Merriman and Warfel (1948) estimated annual pro-2
duction for fishes in Block Island Sound to be 1.1-2.2 g dry wt-m -y Harvey (1950) found the production for pelagic and demersal fish in the English Channel at approximately 1 g dry wt-m2 y1 ; Hellier (1962), at Laguna Madre in Texas, estimated a production of approximately 3.1 g dry wt-m- 2. 1 for the four dominant species; Day et al. (1973), for a marsh-estuarine system in Louisiana, estimated production at 21.8 g dry wt-m-2.y-1; Adams (1976b), in North Carolina seagrass kclm-2 -lI - 2 -lI
beds, estimated production at 21.7 kcal-m-y (%4.6g dry wt-m-2 y)

Assuming 19.85 kJ/g dry wt, the production in the seagrass beds is 0.65 g dry wt-m2 .-1 and in the impoundments 14.8 and 9.66 g dry wt -m-2.y-1. Therefore, the impounded marshes and seagrass beds in Mosquito Lagoon are on opposite ends of the range of yearly production found for marine fish communities.

Production in temperate lentic freshwater fishes has ranged up to 40 g dry wt-m2 .y1. In general, highly productive standing fresh waters in temperate regions produce around 15 g dry wt-m-2. y-1 (Chapman 1978). Tropical and fertilized systems can produce much higher levels. Some tropical lakes are at maximum equilibrium with yields higher than 10 g dry wt-m y (Welcomme 1972). Naiman (1976) reported 155.4 g dry wt-m-2. Y1 in Tecopa Bore, a desert stream in Death Valley, California. Lotic ecosystems are capable of sustaining even higher levels than lentic systems. A phenomenal 197 g dry wt-m2 .y1 was produced in 1967 by 10 species of fish in the River Thames (Matthews 1971).




83


The ratio of production to average biomass can be a useful means of comparing similar aquatic systems as well as providing a general multiplier, which can be considered a secondary productivity function. This function would then allow production to be estimated without measuring more than average biomass (Chapman 1978). The seagrass beds, Sl and S2, had P/5 ratios of 2.36 and 1.90, respectively. The impounded marsh sites, Il and 12, had ratios of 5.24 and 3.59, respectively. Mann (1965) hypothesized that communities with P/9 ratios < 1 were energy limited. If this hypothesis is true, then none of the communities studied would appear to be energy limited. Backiel (1971) found a P/5 ratio of 0.62 for predatory fish in Poland, Hann (1965) found a value of 0.65 for fishes in the River Thames, and MacKinnon (1973) calculated a ratio for a large slow-growing population of American plaice as 0.4. Subsequent studies on the River Thames have given ratios of 2.85 (Burgis & Dunn 1978). Two large freshwater systems, Lake George, Uganda, and Loch Leven, Scotland, had ratios of

1.43 and 2.13, respectively (Burgis & Dunn 1978).

The P/B ratio is also an expression of energy turnover within the fish community. The vast differences in total annual fish production

between the seagrass beds and the impoundments are not simply a result of greater average standing crops in the impoundments but also that the impoundment fishes are turning energy over at a faster rate as shown by their respective P/B ratios. The faster turnover of Il compared to 12 is due to the relatively higher turnover rate (5.3) within the Cyprinodon variegatus population at site Il. At site 12 this same species had a turnover rate of 1.6. In comparing the two seagrass beds, site Sl had the higher rate and was also the bed with




84


the highest percentage of production by the juveniles of seasonal

recruits to the grassbeds. Adams (1976b) found ratios of 2.85 and 2.77

for fish in North Carolina seagrass beds. He attributed these high

turnovers to production by juveniles which he estimated at 79% and 84% of the total annual production for all species. High juvenile production would also appear to partially explain the very high turnover of

18.6 found by Day et al. (1973) in a productive Louisiana estuary.


Respiration

The seasonality of median water temperature appreciably influenced the balance of production to respiration during the year. The ratios ofR/5 during January at sites Il, 12, Si, and S2 were 0.29,

0.18, 0.22, and 0.15, respectively. During August, the ratios at these same sites were 0.92, 0.94, 1.49, and 1.44, respectively.

The annual respiratory losses at sites Il, 12, S1, and S2 were 512, 655, 60, and 81 J-m-y , respectively. The ratios of total

annual resp-iration to average biomass, in the same order, were 8.77, 12.20, 10.94, and 11.79. Day et al. (1973), without compensating for temperature, calculated the same ratio to be 13.16 for fishes in a Louisiana estuary, and Adams (1976b), who did compensate for temperature, reported a ratio of 8.88 for the fishes in a North Carolina seagrass bed. In the shallow-water habitats studied here, standing crops were positively correlated with water temperature. This was also the case in both the Louisiana and North Carolina fish communities. Therefore, the wide range of monthly respiratory energy losses within the fish community results because fish densities are greatest at the




85


same time higher water temperatures are producing higher rates of metabolism and vice versa.


Consumption


Consumption is a more appropriate indication of the functional significance of the fish community in turning over energy within the aquatic ecosystem than is production per unit area because it includes production and energy losses due to respiration. A classic example of this is the work of Davis and Warren (1965) who studied trophic relationships of cottids in an experimental stream. They found that, to a point, production increased with biomass, but then it began to fall as biomass increased further. Due to the increased interaction of individuals at higher levels of fish biomass, most of the food available was used for maintenance; at lower levels of biomass more of the available food was converted to growth.

The calculated annual consumption of each species at each site is presented in Tables 28, 29, 30, and 31. Total consumption per unit area within the impounded marsh was approximately an order of magnitude higher than that occurring in the seagrass beds. Within the impoundments, Cyprinodon variegatus accounted for 44% of the annual consumption. Lucania parva, Poecilia latipinna, Gambusia affinis, and Menidia peninsulae consumed 19%, 8%, 7%, and 1% of the total, respectively. In the seagrass beds, the majority of the consumption was within the populations of Lucania parva (37%) and Menidia peninsulae (270"). The seasonal recruits to the seagrass beds accounting for the greatest consumption were Bairdiella chrysoura with 9% and Lagodon rhomboides with 6%. Lagodon rhomboides consumed 64% of the total




86


energy intake in a North Carolina estuarine fish community (Adams

1976b).

The fish communities are estimated to have consumed a total of 992-1,059 kJ-m2 .y1 in the impoundments and 91-118 kJ-m2 .y1 in the seagrass beds. In a highly productive Louisiana estuary, the fish community consumed 1,257 kJ-m-2.y-1 (assuming 1 g dry wt = 19.7 kJ) (Day et al. 1973) and in a Bogue Sound seagrass bed approximately 418 kJ-m-2.y-1 were consumed by the fishes (Adams 1976b).


System Efficiencies, Turnovers, and Budgets


The ratio of respiration to consumption (R/C) is an index of the efficiency of energy dissipation within a system. The R/C ratio for each community is presented in Tables 28, 29, 30, and 31. The impoundments, Il and 12, had R/C ratios of 0.52 and 0.62, while the ratios in the seagrass beds, Sl and S2, were 0.66 and 0.69, respectively.

The conditions in the impoundments and seagrass beds seem to span the normal range of conditions found in other fish communities. A ratio of 0.61 was found for fishes in the seagrass beds of Bogue Sound (Adams 1976b), 0.62 for an American plaice population in temperate waters (MacKinnon 1973), 0.67 for a freshwater fish community in Poland (Backiel 1971), and 0.73 for the total fish community in the River Thames (Mann 1965). Day et al. (1973), in computing the energy budget for a Louisiana estuary, assumed an assimilation efficiency of 50%, which is significantly different from the 80% assimilation assumed in this study. Therefore, his R/C of 0.24 is believed to be unrealistically low.








Table 28. Total annual respiration, production, and consumption at site Il.


Species Respiration (R) Production (P) Consumption (C) P/C R/C P/R
(J-m-2 y- I) (J -m- 2. Y- ) (J -m- 2-y y )

Cyprinodon variegatus 431208 245746 846243 0.29 0.51 0.57
Fundulus grandis 528 249 971 0.26 0.54 0.47
Gambusia affinis 6493 276 8461 0.03 0.77 0.04
Lucania parva 10668 545 14016 0.04 0.76 0.05
Menidia beryllina 14826 31949 58469 0.55 0.25 2.15
Menidia peninsulae 7502 1428 11163 0.13 0.67 0.19
Microgobius gulosus 1663 470 2666 0.18 0.62 0.28
Poecilia latipinna 39055 693 49685 0.01 0.79 0.02
Syngnathus scovelli 52 106 198 0.54 0.26 2.04
Others 147 ---- 184 ---- .8 ----


512142 281462 992056


Total Fish Community


0.28 0.52 0.55







Table 29. Total annual respiration, production, and consumption at site 12.


Species Respiration (R) Production (P) Consumption (C) P/C R/C P/R
(J.m-2.y-1) (J.M-2.y-') (Jn--2.y-')

Anchoa mi tchilli 459 ---- 574 ---- 0.80 ---Cyprinodon variegatus 42756 5339 60119 0.09 0.71 0.12
Floridichthys carpio 72 90 203 0.44 0.35 1.25
Fundulus grandis 28200 22634 63543 0.36 0.44 0.80
Gambusia affinis 102546 6543 136361 0.05 0.75 0.06
Gobiosoma robustum 78 ---- 98 --~- 0.80 ---Lucania parva 239405 55639 368805 0.15 0.65 0.23
Menidia beryllina 4836 411 6559 0.06 0.73 0.08
Menidia peninsulae 151817 86160 297471 0.29 0.51 0.57
Menidia sp. 549 241 988 0.24 0.56 0.44
Microgobius gulosus 4859 2500 9199 0.27 0.53 0.51
Poecilia latipinna 77315 11957 111590 0.11 0.69 0.15
Syngnathus scovelli 2328 236 3205 0.07 0.73 0.10


191750 1058715


0.18 0.62 0.29


655220


Total Fish Community







Table 30. Total annual respiration, production, and consumption


Species Respiration (R) Production (P) Consumption (C) P/C R/C P/R
(Ji-2.y-1) (J-m 2.y-) (Jm- 2.y-1I

Anchoa mitchilli 946 326 1590 0.21 0.59 0.34
Bairdiella chrysoura 4395 2202 8246 0.27 0.53 0.50
Cynoscion nebulosus 783 486 1586 0.31 0.49 0.62
Eucinostomus sp. 44 154 248 0.62 0.18 3.50
Gobiosona robustum 3114 865 4974 0.17 0.63 0.28
Haemulon sciurus 773 ---- 967 ---- 0.80 ---Hippocampus sp. 25 25 63 0.40 0.40 1.00
Lagodon rhomboides 3698 2066 7205 0.29 0.51 0.56
Leiostomus xanthurus 303 111 518 0.21 0.58 0.37
Lucania parva 28406 203 35761 0.01 0.79 0.01
Menidia peninsulae 11109 4448 19446 0.23 0.57 0.40
Microgobius gulosus 2860 1147 5009 0.23 0.57 0.40
Syngnathus scovelli 2812 414 4033 0.10 0.69 0.15
Brevoortia sp. 364 198 703 0.28 0.52 0.54
Others 562 309 1089 0.28 0.52 0.55


60194 12954 91438


at site SI .


o. 14 o.66 0.22


Total Fish Commviunity







Table 31. Total annual respiration, production, and consumption at site S2.


Species Respiration (R) Production (P) Consumption (C) P/C R/C P/R
(Jm- 2. y- 1) (J-m- 2. y- 1) (J.m-2. y- 1)


Anchoa mitchilli Bairdiella chrysoura Cynoscion nebulosus Eucinostomus sp. Floridichthys carpio Gobiosoma robustum Lagodon rhomboides Lucania parva Menidia beryllina Menidia peninsulae Microgobius gulosus' Opsanus tau Poecilia latipinna Syngnathus scovelli Achirus lineatus
Others


Total Fish Community


87 6991
202 651
72
1583 2689 30981
32
27882 3058 380 23
5220
154
1435


81440


21
2191


39


723 2567 2289 3599


9
1609


6'


135 11478
253 863
90
2883 3361
41935
40
37714 8321
475 40
8536 193
1801


13053 118116


0.16 0.64
0.19 0.61
---- 0.80

0.05 0.75
---- 0.80

0.25 0.55
---- 0.80

0.06 0.74
---- 0.80

0.06 0.74
0.43 0.37
---- 0.80

0.23 0.58
0.19 0.61
---- 0.80

0.003 0.80


0.11 0.69 0.16


t0


0.24 0.31


0.06


0.46 0.08


0.08
1.18 0.39 0.31


0.004




91


In comparing this study's seagrass beds, sites Sl and S2, with the impounded marsh, Il and 12, the fishes of the impoundments appear to be using less of their consumed energy for metabolic purposes relative to production than the fish communities of the seagrass beds. One possible explanation for this is that the several species of atheriniform fishes that dominate the impoundments are well adapted to the rigors of environmental fluctuations typical for impoundments (Snelson 1976). However, as noted earlier, during this study the impoundments appeared to be subject to less stress, in terms of salinity and temperature, than were the shallow seagrass beds.

Evidence that appears to support the idea that the seagrass beds are indeed physiologically more stressful than the impoundments are the R/C ratios of the two species that occur most frequently in both impounded and seagrass habitats, Lucania parva and Menidia peninsulae. Lucania parva had an average R/C ratio of 0.71 in the impoundments and

0.77 in the seagrass beds. Menidia peninsulae had an R/C ratio of

0.59 in the impoundments and 0.66 in the seagrass beds. In both cases, the seagrass bed population of each species was using more of its consumed energy for metabolic purposes than for growth. Other explanations such as increased search time for prey are possible, and probably are operating, but are not believed to be as significant as physiological stress (Adams 1976a, Cameron 1969). In discussing why the eelgrass fishes of Bogue Sound were apparently apportioning a lower percentage of consumption to respiration, Adams (1976b) discussed the "adaptation to stress" explanation above. Adams also went on to develop a second hypothesis that abundant energy supplies available within the eelgrass systems may be favorable enough to overcompensate




Full Text

PAGE 1

THE STRUCTURE AND FUNCTION OF WARM TEMPERATE ESTUARINE FISH COMMUNITIES BY JAMES K. SCHOOLEY A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 1980

PAGE 2

ACKNOWLEDGEMENTS Portions of this project were supported by a grant from the Division of Sponsored Research, the University of Florida, to Dr. Stephen Bloom. Sampling support was provided by the Merritt Island Wildlife Refuge, NASA's Kennedy Space Center, and LeFil's fish camp in Oak Hill, Florida, and is gratefully acknowledged. Drs. Stephen Bloom, Frank Maturo, and Robert Virnstein and the staff of the Harbor Branch Foundation of Fort Pierce, Florida, provided valuable assistance in the identification of zooplankton and benthic invertebrates. This project benefited tremendously from discussions with Dr. William Carr of the Whitney Marine Laboratory of the University of Florida. Dr. Jack Ewel graciously provided advice and equipment for the calorimetric analysis and Mr. Robert Twilley provided help in the analysis of mangrove forest structure. Field work and laboratory processing were greatly facilitated by a large group of volunteer assistants that I would like to acknowledge: David Brown, Fred Boyd, Kathy Cavanaugh, Diane Despard, J. B. Frost, Nancy Ing, Ginny Kittles, Blaise Kovaz, Beth Meerman, Jeff McGrady, Andy Roth, Bill Szel istowski , Linda Warner, Chris Wolniewicz, David Yarnell, and Milito Zapata. The thoughtful review of early drafts of this manuscript by Drs. Frank Nordlie, Thomas Emmel , Carter Gilbert, Jerome Shi reman, Stephen Bloom, and Martha Crump and Kathryn Schooley is gratefully acknowledged. ii

PAGE 3

TABLE OF CONTENTS PAGE ACKNOWLEDGEMENTS ii LIST OF TABLES iv ABSTRACT vii INTRODUCTION 1 STUDY AREA 6 METHODS 8 Physical Data 8 Zooplankton 9 Benthic Infauna 9 Primary Production Processes 10 Fishes 11 Cal orinietric Processing 15 Production 17 Respiration 18 Consumption and Energy Budgets 19 RESULTS 21 Physical Environment 21 Primary Production 26 Zooplankton 26 Microbenthos 33 Epibenthic Invertebrates 40 Fish Community Structure 42 Fish Community Function 63 DISCUSSION 73 Abiotic Factors 73 Biotic Factors 76 Production 81 Respiration 84 Consumption 85 System Efficiencies, Turnovers, and Budgets 86 Fish Community Summary 97 REFERENCES CITED 10] BIOGRAPHICAL SKETCH 107 i i i

PAGE 4

LIST OF TABLES TABLE PAGE 1 Age class groupings of common seagrass and impoundment fishes in mm of standard length 16 2 Median water temperatures and average monthly air temperatures during the sampling period; absolute minimum, absolute maximum and temperature ranges from submerged maximum/minimum mercury thermometers 23 3 Salinity at each site monthly and total rainfall at Cape Canaveral 24 -2 -1 4 Net primary production (kJ-m ^y ) entering the aquatic system at site II 27 5 Net primary production and standing crops of seagrasses at sites SI and S2 27 6a Mean standing crop of zooplankton (Number/m-^) , September to November 1978 at each sampling site 28 6b Mean standing crop of zooplankton (Number/m"^) , December 1978 to February 1 979 at each sampling site 29 6c Mean standing crop of zooplankton (Number/m"^) , March to May 1979 at each sampling site 30 6d Mean standing crop of zooplankton (Number/m"^) , June to August 1 979 at each sampling site 31 7 Site Il's average quarterly and average annual densities and standing crops of energy for the major groups of benthic invertebrates 34 8 Site 12' s average quarterly and average annual densities and standing crops of energy for the major groups of benthic invertebrates 35 9 Site Si's average quarterly and average annual densities and standing crops of energy for the major groups of benthic invertebrates 36 10 Site S2's average quarterly and average annual densities and standing crops of energy for the major groups of benthic invertebrates 37 iv

PAGE 5

i TABLE PAGE n The values and authorities cited used to convert standing crops on a dry weight basis to standing crops on an energy basis, for the benthic invertebrate groups common in the impoundments and seagrass beds 38 12 Percentage of the average annual standing crop of energy for major benthic invertebrate groups at each site 39 13 Average annual density and standing crop of energy of common large decapods at each site 41 14 Fish collected at site 11 43 15 Fish collected at site 12 44 16 Fish collected at site SI 45 17 Fish collected at site S2 48 18 Total fish densities at each site 52 19 Fish standing crops of energy at each site 53 20 Percentage of average annual density and standing crop of energy for the major fish species at each site .... 54 21 Correlations (Spearman Rank) of structural characteristics of the fish communities at each site with monthly salinity, median water temperature and seagrass density . 56 22 Mean energy content of juveniles and adults of all species at each site 58 23a Mean energy content of common species at site II 59 23b Mean energy content of common species at site 12 60 23c Mean energy content of common species at site SI 61 23d Mean energy content of common species at site S2 62 24 Site II respiration and positive production values in J/m^ 54 25 Site 12 respiration and positive production values in J/m^ 65 V

PAGE 6

TABLE ' PAGE 26 Site SI respiration and positive production values in J/nT^ 67 27 Site S2 respiration and positive production values in J/m^ 59 28 Total annual respiration, production, and consumption at site II 87 29 Total annual respiration, production, and consumption at site 12 88 30 Total annual respiration, production, and consumption at site SI 89 31 Total annual respiration, production, and consumption at site S2 90 vi

PAGE 7

Abstract of Dissertation Presented to the Graduate Council of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy THE STRUCTURE AfID FUNCTION OF WARM TEMPERATE ESTUARINE FISH COMMUNITIES By James K. School ey December 1980 Chairman: Frank G. Nordlie Major Department: Zoology The seagrass beds of Mosquito Lagoon and the nearby impounded marshes are the most northern portions of the Indian River and lie on the east central coast of Florida. A study of the seasonal fluctuations in water temperature, salinity, benthic invertebrate communities, and macrozooplankton standing crops ivas combined with estimates of annual detrital input to interpret differences in the structure and function of the fish communities in the impounded marshes and the open seagrass beds of the lagoon. The two impounded marsh sites under study had salinity ranges of 10-28°/oo and 25-38°/oo during the period of this study. The ranges of water temperatures in the impoundments were 6-37°C and in the seagrass beds, 8-39°C during this study. Based on monthly fluctuations in salinity and temperature, it was concluded that the impoundments were no more physiologically stressful for resident fish than the seagrass beds. Net detrital input to the shallow impoundment was 4,306 kilojoules^ -2 -1 m -year , 75% of v/hich came from black mangrove litter-fall. Net vi i

PAGE 8

detrital production by the seagrasses in the open lagoon sites was -2 -1 2,413-3,707 kJ-m -y . The macrozooplankters most common to each site were calanoid copepods, caridean shrimp, and nematodes. Seagrass beds had higher densities of caridean shrimp and brachyuran larvae. The benthic infauna was dominated by bivalves in the impoundments and polychaetes in the seagrass beds. The absence of large decapods, especially blue crabs, and the limited fish fauna of the impoundments are suggested as reasons for the vastly different benthic communities found in the two habitats. Structurally, the fish communities of the impoundments were dominated by several species of fishes in the order Atheriniformes. Most common were Cyprinodon variegatus , Poecilia lati pinna , Gambusia affinis , Lucania parva , and Menidia peninsulae . The clown goby, Microgobius gulosus , was also consistently found. In the seagrass beds, the dominant resident community members were Lucania parva , Menidia peninsulae , Microgobius gulosus , Gobi o soma robustum , and Syngnathus scovelli . Significant seasonal recruits to the seagrass beds, primarily represented as juveniles, were Lagodon rhomboides and Bairdiella chrysoura . Average fish densities in the impounded marsh were 16.5-27.5 (Ind/m ) and in the seagrass beds, 3.6-7.3 (Ind/m^). Average fish standing crops were 53.7-58.5 kJ/m^ in the impoundments and 5.5-6.9 2 . kJ/m in the seagrass beds. Complexity of community structure was positively correlated with median water temperature at all sites. At only one of the two seagrass sites was there a significant positive correlation between community structure and seagrass density. Functionally, the impoundment fishes were estimated to have consumed 992-1 ,059 kJ.m"^.y"\ respired 512-655 kJ-m'^.y""" and had a net V i i i

PAGE 9

production of 192-281 kJ-m" -y"'. In contrast, the seagrass bed fishes 7 -1 are estimated to have consumed 91-118 kJ«m -y , respired 60-81 -2-1 9 1 kJ-m and had net fish productions of 13 kJ.m'^.y" . The turnover rates of energy for the impoundment fishes were 3.6-5.2 per year, while the seagrass beds were 1.9-2.4 per year. The impoundment fishes appear to be more efficient at converting consumed energy into net fish production than the seagrass bed fishes. The efficiencies of other energy transfers, the influence of herbivore/detriti vores , and fish generation times are discussed in comparing the two fish community types to each other and to other aquatic systems in general. ix

PAGE 10

INTRODUCTION Few researchers have attempted to assemble an ecosystem model for shallow estuarine systems. Notable attempts at structurally and functionally describing these complex systems in terms of energy flow are Day et al . (1973) for Barataria Bay in Louisiana, Odum et al . (1974) for Crystal River, Florida, and Thayer et al . (1 975a ) for the grass beds of the Newport River, North Carolina. Except for the Crystal River study, most models are the result of the synthesis of community and population studies, only some of which may have contemplated integration into an ecosystem model. In attempting to synthesize previous studies into models, structural characteristics are often better understood than are functional characteristics of the various communities or populations within the ecosystem (Day et al. 1973). This is also usually the case for estuarine fishes. Even though a variety of structural references concerning species composition, seasonality, and, in some cases, density, is available for most larger estuarine systems, very little information on the energetic functioning of fishes is available. These functional characteristics would include estimates of respiration, production, and consumption. Excellent contributions to our understanding of the consumption process, and ultimately energetic functioning, include the Harringtons' (1951) food selection study of salt marsh fishes, Odum and Heald's (1972) trophic analysis of the North River estuary in south Florida, Carr and Adams' (1973) classic analysis of the ontogenetic 1

PAGE 11

2 feeding changes of fishes in seagrass beds of west Florida, and Whitfield's (1980) work on the energy flow in a south African estuary. The work by Adams (1976a, b) on the fish communities in Zostera beds in the Newport River estuary. North Carolina, is an excellent example of a study that structurally and functionally describes a community and is later integrated into an ecosystem model (Ferguson and Adams 1979). One estuarine system that only recently has come under intensive study is that of the Indian River on Florida's east central coast, the northern portion of which is shown in Figure 1. Gilmore (1977) has done a summary of the geography and hydrology of the Indian River in his review of the fish fauna of the region. Prior to the mid-1 950' s, the high marshes within the Indian River were accessible to fishes of the open lagoon. However, since then, nearly all high marsh has been isolated from the lagoon by earthen dikes for mosquito control purposes (Provost 1969, 1973). On Merritt Island, this resulted in over 22 hectares of marsh being isolated, as well as partitioned by these dramatic management practices (Provost 1969, 1973). Snelson (1976) has done a preliminary survey of the fishes of the various impounded marsh habitats of northern Merritt Island. The impact of this impoundment on the entire estuarine fish community has never been evaluated. Without the experimental control of a similar large estuary with an unimpounded marsh such a determination would be difficult. One aspect of fish community ecology that is testable within this modified system is the impact of this isolation on the populations of several species that are common to both the impoundments and seagrass beds (Snelson 1976. Gilmore 1977). These populations will serve as

PAGE 12

1—1 OvJ a +-> to (O a 5cn 13 (0 o CU Q. to _E II II O to c o +-> u -o O 0) J3 C7) (/) C CO •rfO SCL O) E (O rO (U 1/5 to O II c: (O S> •rC^O 1—1 c o +J 1—1 oj sc OJ 3 -C o +-> Q. SE O TII I— • i3

PAGE 13

4

PAGE 14

5 excellent ecological indicators of the relative differences in structure and function between fish communities in the impounded marsh and those in the seagrass beds. The objectives of this study are (1) to examine and compare the structure and energetic functioning of fish communities in impounded marsh and open seagrass beds; (2) to elucidate relationships between the observed properties of the fish communities and abiotic and biotic factors; (3) to characterize the functional aspects of the fish communities in terms of efficiencies of transfer in order to compare the systems studied to other aquatic systems in general ; (4) to provide information useful in developing ecosystems models of the impounded marsh and seagrass beds.

PAGE 15

STUDY AREA The northern Indian River and Mosquito Lagoon are shown in Figure 1. The term "river" is a misnomer. Indian River is a large, shallow, mesohaline lagoon that extends 250 kilometers along the east central coast. The lagoon is separated from the ocean by a barrier island that is cut in five places by artificial inlets. In the northern portion of the system this barrier island is at its widest and is known as Merritt Island. The Mosquito Lagoon is separated from the rest of the Indian River by a second strip of land. This land has been cut at the Haul over Canal to form a passageway for the intracoastal waterway. The closest access to the ocean from Mosquito Lagoon is through the Ponce de Leon Inlet, 80 kilometers north of Haulover Canal, just off the map shown in Figure 1. The average water depth of Indian River is 1.5 m, with the maximum depths in areas dredged for channels, harbors, and land fill. The bottom of the lagoon is covered by extensive seagrass beds, dominated by Halodule wrightii and Syrinogodium filiforme . In the northern part of the system (Fig. 1), tidal fluctuations are insignificant; the major water movements are the result of wind-driven circulation (Dubbelday 1975). Lasater (1975) reported that in Mosquito Lagoon, salinity ranges from 21-367oo, with a yearly average of 31.17oo. Because of the lack of significant fresh water input, the salinity of the lagoon at any given time represents a balance between evaporation and local precipitation (Lasater 1975).

PAGE 16

7 Two seagrass beds within the Mosquito Lagoon were studied. The first, SI, is located in Eddy Creek at the southern end of the lagoon, where water depth was approximately 0.5 m. The second seagrass site, S2, was located off of an area known as Van's Island, approximately 18 km from SI. Water depth at S2 was approximately 0.6 m. In contrast to the relative homogeneity of the system of seagrass beds, the impounded marshes of Merritt Island and the barrier island east of Mosquito Lagoon do not have a uniform flora either in species composition or species density (Snelson 1976). This is due partially to variations in salinity and water level resulting from differing degrees of isolation among the impoundments. In the impoundment at the southern end of the Mosquito Lagoon studied here (II) the marsh was broken by large expanses of water bordered by stands of black mangrove ( Avicennia germinans ); however, some white mangrove ( Laguncularia racemosa) and button mangrove ( Conocarpus erecta ) were also present. The open waters were found to have seasonal growths of Chara , which in some locations filled the water column. The northern impoundment canal (12) was located approximately 200 m from site S2. This canal, formed by dragl inning, is nearly continuous around the periphery of Van's Island and is approximately 1.25 m deep with a width of 15 to 20 m. During the dry season, it is the only standing water in the area sampled; however, during the rainy season this canal is only a part of the large marsh surface covered by water. The dominant vegetation was low-fringing black mangroves with some button mangroves along the dike and occasional growth of Chara.

PAGE 17

METHODS Sampling was done once each month during the period July 1978 through August 1979 for sites II, SI, and S2. Site 12 was sampled monthly from August 1978 through August 1979. Each sampling effort consisted of measuring air and water temperature, salinity, depth, and submerged macrophyte density and collecting samples of macrozooplankton, fish, and larger epibenthic invertebrates. Benthic infauna were collected quarterly at each site in October 1978 and January, April, and July 1979. Site II was also sampled in May 1979. Physical Data Physical data collected at each site included measurements of air temperature in the shade, water temperature, salinity, and water depth in the areas sampled for fish. Maximum-minimum thermometers were submerged at sites II, 12, and S2, and readings were taken each month and the thermometers reset. Salinity samples were taken at mid-water depth and analyzed using a temperature-correcting optical refractometer . In November 1979, surface sediment samples were taken at II and S2 and the percentage of combustible material determined by ignition in a 475°C oven for 8 hours. Rainfall and average monthly air temperatures are from recordings taken at Patrick Air Force Base 60 km south of Mosquito Lagoon. 8

PAGE 18

9 Zooplankton Each month, three replicate 10-m length tows were taken at each site using a 363 y mesh net with a diameter of 0.3 m and length of 1 m. The contents of each tow were individually preserved in 5% buffered formalin. Beginning in October ctenophores were counted prior to preservation. Ctenophores in earlier samples broke down rapidly and are, therefore, underestimated in data from July through September 1978. Specimens were identified only at the most practicable taxonomic level during sorting and counting. Prior to sorting samples with a large amount of flocculent material, a small amount of dissolved rose bengal was added to stain the plankton and improve sorting efficiency. The mesh size and length of tows were expected to produce comparatively dilute plankton samples but were considered adequate for the purpose of making a qualitative comparision between the impoundments and seagrass beds. Benthic Infauna Sampling the benthic infauna was done at a random location adjacent to the areas seined for fish. Five adjacent cores were taken from this area using a PCV coring tube with an inner diameter of 10.5 cm driven to a depth of 10 cm of solid sediment. Each core sampled 86.6 cm^ of bottom area. At site II this produced a sample of 7-10 cm of flocculent material on top of the 10 cm of consolidated sediments. Sites 12, SI, and S2 did not have deep layers of unconsolidated material . The contents of each core were sieved in the field to retain materials larger than 500 microns. The retained material was

PAGE 19

10 preserved in 10% buffered formalin. After sorting and identification of core contents, representative subsamples were taken to determine dry weights and, for some gastropods and bivalves, ash-free dry weights per individual. Standing crops of dry weights were converted to standing crop energy units by using published energy content values (Cummins and Wuycheck 1971, Thayer et al . 1973, Whitfield 1980). Primary Production Processes The above-ground standing crop of macrophytes from five randomly thrown 0.25 m quadrats was harvested each month. Samples were taken in waters 50-75 m from shore at sites SI and S2, along the edge of the canal at 12, and 25-50 m from shore at II. The harvest from each toss was returned to the lab, where shell and detrital materials were rinsed off prior to drying to constant weight at 80°C. The yearly net primary production of seagrass at sites SI and S2 v/as calculated as two times the maximum standing crop (McRoy and McMillan 1977), assuming 1 mg dry weight is equivalent to 16 joules. The contribution of epiphytes to seagrass community net production was not evaluated; present work by the Harbor Branch Consortium (R. A. Gibson, personal communication) may shed some light on the contribution of epiphytes to net production within the seagrass beds of the Indian River. Net primary production for site 11 was computed in two components: the contribution of the green algae Chara and the litter fall from the mangroves, primarily blacks ( Avicennia ). Production for Chara was calculated at 1.5 times the maximum standing crop (Rich et al. 1971);

PAGE 20

mangrove litter production was calculated after determining a leaf area for the mangroves during the summer of 1979. Leaf area was calculated using the modified plumb-bob technique used by Benedict (1976). The technique was applied at five random sites, with ten replicates at each site. Production was then calculated using a ratio of leaf area index to litter production for Florida mangrove forests derived from Pool et al. (1974). Based on forest descriptions in Pool et al. (1974) leaf turnovers per year were assumed to be 1.0 and the ratio of leaf litter to wood litter to be 3:1. Dead leaves prior to falling were assumed to contain 20.17 J/mg (Heald 1969) and twigs 17.86 J/mg (Golley 1961) on a dry weight basis. The percentage of marsh covered by open water versus mangrove canopy was determined by planimetry (cut and weigh) of recent aerial photographs of the II sampling area. This provided a proration to use in computing total marsh production from Chara and mangrove production data. At site 12, the impoundment canal, the input of detritus was considered to be a complex interaction, varying with the season, of variable water transports to and from the impoundment flats. Therefore, an estimate of net primary production available within the canal habitats would be premature, based only on limited Chara and fringing mangrove production data. Fishes Shrimp, crabs, and fish were quantitatively sampled each month at sites II, SI, and S2 by open-water seining as shown in Figure 2. Each net was 10 m in length, with a bar mesh of 3.18 rm. The sampling team

PAGE 21

X (U •M 4J fT3 a. Ol C OJ CD Q. 00 O OJ Q. r— o ro •rJ fO (T3 E 1 E Q. fd X s_ OJ CD ra 1. •ro Q MCM

PAGE 22

13

PAGE 23

14 proceeded as a tight group to the edge of the area to be sampled, and immediately deployed the two nets, a sweep and a barrier, at right angles to each other. The barrier net was set perpendicular to the beach area and the sweep net, set on the deep water end of the barrier, was swept toward the shallows. The 10-m sv/eep net was tethered at a fixed distance of 6.1 m, sampling a bottom area of 33 m . The two nets were pursed and removed from the water for sorting. Site 12, the impoundment canal, was sampled using a beach seine. The sweep net was run out 6.1 m from the shoreline and perpendicular to it. The net was 2 then swept to the beach. This covered 33 m of area, as in the openwater seining. Because the canal was approximately 1.1 m deep at the end of the 6.1 m sweep net, the volumes of water swept in the two techniques were comparable. Three replicate quantitative samples were taken at each site. Early attempts using a portable drop net (Adams 1976a) that sampled an area of 9 m were found to be very labor-intensive and did not significantly alter the density, species number, or size classes found using open water seining. Gilmore et al. (1976) discussed the effect of sampling with drop nets for Indian River seagrass systems. He pointed out that due to the size of open sand and grass patches, drop samples can be strongly biased, while larger samples from seining cover a greater diversity of open sand and seagrass areas may be less biased. However, extremely large seines can underestimate several groups such as the gobies and pipefishes. The techniques used here are an attempt to compromise between drop-net and large sweep-net techniques , Fish and invertebrate species collected were bagged in plastic and stored on ice. Samples were returned to the lab for processing as

PAGE 24

1= i I soon as possible. Fish and invertebrates were sorted and identified; the fish were partitioned into standard length-size ranges of 5 mm, i.e. ! 0-5 mm, 6-10 mm, etc; crabs were measured across the width of the ! carapace. After drying for 48 hrs in a forced air oven at 80°C, dry weights were recorded for each size class group for each species of fish, for the total of each shrimp sample, and for each crab individually. A qualitative seine sweep was taken each month at sites SI and S2 with a 20 m bag seine, also of 3.18 mm bar mesh. An area of 10002000 m was swept at each site. Fish and invertebrates collected were sorted and any species not found in the quantitative seine were preserved in 25% buffered formalin. The remaining catch was subsampled to augment the various size class categories of species collected in I the quantitative seines to provide an adequate sample size, in terms of mass, for calorimetry. The samples were separately bagged and also stored on ice for immediate processing and drying on returning from the field. Calorimetric Processing After recording dry weights of individual size classes for each fish species, the various size classes of the dominant species were grouped into age classes (Table 1) according to the technique of Adams (1976a). These samples were then processed according to the general procedures outlined by Cummins and Wuycheck (1971); hov/ever, no carbonate fractions were determined. For determination of ash-free dry v/eights, subsamples were burned at 475°C for four hours to avoid burning off carbonates (Paine 1971). Calorimetry was done using an

PAGE 25

16 Table 1. Age class groupings of common seagrass and impoundment of fishes in mm of standard length. Species Age Class Pre-juv Juven i le Adult Rep Adult Anchoa mi tchi 1 I i <50 >50 Archosargus probatocepha I us 25-50 >50 BairdieMa chrysoura 10-85 >85 Cynoscion nebulosus 25-200 >200 Cyprinodon variegatus 1014 15-24 25-35 Eucinostomus sp. 15-55 >55 Fundulus grandis 15-30 >30 Gambusia affinis <20 >20 Gobiosoma robustum 3-15 >15 Lagodon rhomboides 1550 51-85 >85 Leiostomus xanthurus 17-85 >85 Lucania parva 8-25 >25 Lutjanus griseus 10-175 >175 Men I d i a sp . 20-60 >60 Microgobius gulosus <30 >30 Paralichthys albigutta <95 . >95 Poec ilia 1 at i p i nna <20 >20 Strongylura notata 45-200 >200 Syngnathus scovel 1 i <60 >60 Trinectes maculatus 18-45 >45

PAGE 26

17 automatic adiabatic calorimeter equipped with a digital thermometer, printer, and programner (Parr Instrument Company, Moline, Illinois). Operating procedures followed the Parr procedures manual directly (Parr 1969). Two 1 g replicate samples were taken for percent water and ash content determination at the same time the three replicate 1 g pellets were pressed prior to bombing. Over 90% of the materials tested gave a coefficient of variation ("C.V.") of less than 1%, using three replicates. The C.V. was less than 3% for 99% of the samples. Golley (1961) and Paine (1971) recognize a coefficient of less than 3% as a satisfactory variation for biological materials. Results are expressed as joules per milligram of ash free dry weight. As defined by Ivlev (1966), production is the total amount of fish tissue produced during any given time interval, including that of individuals that did not survive to the end of that interval. Monthly production is then calculated as the product of the growth per individual and fish numerical density. Production for each species was calculated after Ricker (1946) and Allen (1950) as Production P = GB where £n w„ an w G At is the coefficient of instantaneous growth. B,(e G-Z 1) B is the average biomass, and

PAGE 27

18 -(£n jin Z = -r is the instantaneous coefficient of population change attributable to mortality and migration, and and W2 are the mean weights at time t-j and t2, respectively, and and N2 are the numbers of fishes present at times t^ and t2, respectively. Day et al . (1973), Adams (1976b), and Chapman (1978) discussed some of the important assumptions of the applications of this model. As Adams (1976b) pointed out, estuarine and seagrass fishes usually show marked immigration and emigration which affect estimates of N. This is probably more significant at sites SI and S2 than at II and 12. However, Chapman (1978) pointed out that there is no need to correct production data for the immigration and emigration of fishes, provided fish density and size-class specific growth are estimated often enough to assess abundance and growth during the sampling period. Day et al. (1973) used three-week sampling intervals, while Adams (1976a) used four-week intervals as done in this study. Respiration The resting energy of metabolism ms estimated from Winberg's (1956) equation, Q = 0.321 W^'''^, as a general equation for marine fish at 20°C. Metabolism for each species was calculated at an average weight per individual at the median water temperature during the sampling period by applying Krogh's (1916) temperature correction factors. This rate of oxygen use per hour by one average-weight individual weighing X g dry weight was converted to a population total of joules burned per month at each site using a conversion factor of 14.07 J/mg of oxygen (Mann 1978).

PAGE 28

19 The energy cost specific to utilization of food, apparent specific dynamic action, and the metabolic cost of foraging for food were both found to be significant portions of the energy budgets of fish populations studied by Kerr (1971a,b,c). Reviews by Webb (1978) and Mann (1978) discuss the relationship between resting metabolism and true energy costs in nature. According to Mann (1978), Winberg II, a doubling of the equation above (Winberg I), appears to be a useful approximation of the metabolism of a fish which optimizes its growth rate in nature (Edwards 1968, Ware 1975). Winberg II is used here as the estimate of respiration within the fish community. Consumption and Energy Budgets Annual energy consumption per species in both habitat types was calculated as a percentage of the sum of respiration plus production. Winberg (1956) found assimilation efficiencies for freshwater fishes between 76% and 96.6%. The average val ues assumed were 85% of calories of the diet were assimilated and 15% lost as feces. He also argued that, with a range of 3-7% of the energy lost as urine added to fecal loss, a total of 20% of ingested energy was lost through egestion and excretion. Winberg 's equation as applied here is C = 1.25 (P + R) where C = annual consumption of energy, R = annual metabolic energy loss, P = annual production energy.

PAGE 29

20 Community annual consumption is then compared ^between the various sites. Interspecific comparisons of consumption should be done cautiously, due to the broad range of assimilation efficiencies found for different fish species in nature (Webb 1978). Fish community energy budgets for each site were then constructed by the addition of each species' totals for consumption, production, and respiration during the year. Ecological efficiencies were then calculated for each community and used to compare communities.

PAGE 30

RESULTS Diagrams summarizing the major environmental influences, primary production sources, and energy flows for the impounded marshes and seagrass beds are presented in Figure 3. These diagrams depict the conceptual framework for presentation of the results of this study and the subsequent discussion of each community. Physical Environment The average values and the ranges of temperature and salinity for the four sites show an interesting pattern (Tables 2 and 3). The yearly range of temperatures (Table 2) found in the two impoundment habitats, 11 and 12, and one seagrass bed, S2, were nearly identical; however, the average range per month of temperatures experienced at 12 was significantly smaller (Student's t, p < 0.05) than those ranges for 11 and S2. This reduced environmental flux at 12 is assumed to result from the deeper water buffering rapid daily temperature fluctuations. Site 12 had narrower average monthly temperature ranges than site S2, but not significantly so. Overall, water temperatures closely paralleled the average air temperatures and the two were roughly equal during January, February, and March. Significant differences were found in the average salinities at the four sites. Site II was significantly lower than the other three sites (Student's t, p < 0.01). Site 12 was significantly higher than 21

PAGE 31

22 3 O CO •rO c I/) o s_ c x: s«o E T3 (U TJ C 3 O T3 C ro -D , >, s_ c: (C E E E E c (J sCT.

PAGE 32

23 Table 2, Median water temperatures and average monthly air temperatures during the sampling period; absolute minimum, absolute maximum and temperature ranges from submerged maximum/minimum mercury thermometers. Year £ Month Water TempCC) Air TempCc) 11 12 S2 Cape Canaveral 1978 August 31 .5 25.6 September 31 .0 31.0 31.0 25.0 October 26.0 30.0 2i».0 22.0 November 23.0 23.0 22. 5 22.0 December 21.5 22.5 l^.k 17.0 1979 January 15.0 15.0 15.0 Februrary 16.8 17.5 15.0 March 18.5 19.3 18.5 18.0 Apr i 1 2'f.O 25.5 24.5 22.8 May 27.5 27.0 23.9 June 29.0 31 .5 29.0 26.7 July 20.5 33.0 28.3 August 31 .0 31.3 27.2 Absolute minimum 6.0 8.0 8.0 Absolute maximum 39.0 37.5 39.0 Maximum monthly range width 17.5 15.5 19.0 Average monthly range width IA.7 10.8 15.3

PAGE 33

24 Table 3. Salinity at each site monthly and total rainfall at Cape Canaveral . Year S Month Salinity (°/oo) 1 n f ;^ 11 1 mm^ 11 12 SI S2 r^soo l3na\/of"a 1 1978 August ]k 38 35 18 J'^ September 16 38 32 36 88 October 17 36 38 36 56 November 20 36 3A 1 6 December 28 38 38 38 101 1979 January 10 28 18 25 178 Fph r 1 1 rv I 1 u 1 01 y 1 7 32 20 33 32 March 13 32 22 3k 39 Apr i 1 18 3'» 38 19 May 15 32 2k 30 142 June 20 35 32' 35 116 July 18 3^ 35 3k 85 August 16 36 36 37 228 Average 16 3A 30 3k Range 10-28 28-38 18-38 25-38

PAGE 34

25 SI (Student's t, p < 0.01), while SI and 52 were not significantly different from each other. As was the case with temperature, the stabilizing influence of greater water depth on yearly fluctuations is seen in the narrower range of salinity found at site 12, as compared to the other three sites. In comparing SI and S2, the greater range of salinity at SI is believed to be due to the isolation of the shallow portion of the lagoon where site SI is located (Eddy Creek). This possibly reduces mixing and, consequently, the waters of SI are diluted relatively more during periods of heavy rainfall. The most remarkable change in salinities was a drop of 20°/oo, which occurred at SI from December to January due to the heavy rains the area received in late December and early January. The seasonality of rainfall in the Mosquito Lagoon area would appear to modify the rain's influence on depressing salinity in the system. Two peak periods of rainfall were observed, winter and early summer. During the winter, when rates of evaporation v/ere relatively low, salinity was markedly depressed by heavy rainfall and did not recover rapidly. However, during the summer, a period of rapid evaporation, heavy rains did not depress salinities to the same degree as winter rains, nor for as long a time. Therefore, the seasonality of rainfall, as well as amount, markedly affected both the level and fluctuations of salinity within the shallow water systems studied. The percentage of combustible organic material in the surface sediment at II was over five times greater than that found at SI (22.6% vs. 3.9%). With sample sizes of 9 and 8, respectively, this difference is highly significant (Student's t, p < 0.001). Therefore, the yearly

PAGE 35

26 accumulation of detrital material is assumed to be much greater within the impoundments than in the shallov/ seagrass bed. However, some of the detritus originating in the shallows may possibly be transported from the seagrass beds and deposited in deeper waters of the lagoon. Thomas (1974) found amounts of organic carbon in the sediments of barrow pits and infrequently dredged portions of the intracoastal waterway to be 2 to 3 times higher than the shallower seagrass beds. However, the percentage of net detrital production exported to deeper water storage in the open lagoon is not known. Primary Production Estimates of net primary production for three sites are presented in Tables 4 and 5. The ratio of mangrove production to Chara production within the impoundments was approximately 4:1. The ability to extrapolate from the estimates for II to the entire impounded marsh has not been demonstrated. Analysis of infrared aerial photographs to determine plant surface areas within the impoundments is now being attempted using facilities of the Kennedy Space Center. However, the spectral sensitivity of films presently available does not appear to be great enough and will delay estimates until a great deal of ground-trutti work is done. Zooplankton The twelve months of zooplankton collections were divided into four seasonal quarters (Table 6) based on rainfall and air temperature patterns (Tables 2 and 3). By taking the average of the collections for each of the three month periods, some of the temporal

PAGE 36

27 Table 4. Net primary oroduction (kJ-n" .y" ) entering the aquatic system at site II: units qiven fnr each value, numbers in oarentheses are one standard error, N--sample size. Site II Mangrove Leaf area index 1.66 (0.'47), N = 50 Leaf weight/leaf area (g/m^) I80 (51), N 10 Net production as litter into 7^63 the aquatic system (kj'm'^-y'') Percentage of narsh covered kS% by mangroves Net Production (kj -m"^ y" ' ) 3^33 Chara Maximum standing crop (g/m^) 63.98 (51.66), N = 5 Minimum standing crop (g/m^) 0.0, N = 5 Net production in open I6't8 (1331) water (kj-m"^.y-') Percentage of open water 53^ Net Production (kj-m"^-y"') 873 (705) Total marsh net production '43O6 (kJ-m-^-y-') Table 5. Net primary production and standina crops of seagrasses at sites SI and S2; numbers in parentheses are one standard error, N--sample size. SI S2 Maximum standing crop (g/m^) 75-83 (2i..37), 116.5 (20. I^*) N = 5 N = 5 Minimum standing crop (g/m^) 12.11 ('4.;.) , 8.7't (e.j't) , N 5 N » 5 Net Production (kJ-m ^-y"') 2'<1 3 (387) 3707 '320)

PAGE 37

28 Table 6a. Mean standing crop of zooplankton (Number/m^), September to November 1978 at each sampling site. Taxa 11 12 SI S2 v/ii 1 ua r 1 ans 1 . 6 0.2 1.0 Nematodes 21.0 0.8 0.5 2.8 Pol ychaetes 0.3 0.6 0.8 0.3 Gastropods 2.0 0.2 D 1 Va 1 ve 3 0.6 US L r acou s 12.0 0.2 0.2 2.7 Copepod larvae 0.7 Calanoid copepods 1 .0 1 .0 1.7 5.6 Cyclopoid copepods 0.2 0.3 Harpacticoid copepods 0.2 1 .0 1.0 Cypris larvae 0.2 Mys ids 0.2 Amph i pods 0.5 Caridean shrimp 1.2 O.i) 2.0 15.1 Brachyuran larvae 0.2 0.2 1.0 1.0 Larvaceans 3.3 Chaetognaths 0.2 0.2 2.1 Other taxa 1.6 0.8 0.7 Total ko.o 5.1 12.3 33.2

PAGE 38

29 Table 6b. Mean standing crop of zooplankton (Number/m ), December 1978 to February 1979 at each sampling site. Taxa 11 12 SI S2 Cnidarians — — — 0.6 Ctenophores — 0.1 1.9 Nematodes 183.0 6.1 25.5 13.0 Pol ychaetes 0.2 2.7 1.0 1 .0 Gastropods 1 .A — — — Bi va 1 ves — 1.1 0.7 Ostracods 1.6 0.2 8.8 3.5 Calanoid copepods 85.0 8.8 9.1 Cyclopoid copepods 1.2 0.3 2.1 O.k Harpacticoid copepods 1.9 1.7 1.0 Cypris larvae — — — .0.1 Mys ids — 0.7 — Cumaceans — 0.2 0.3 0.3 1 sopods 0.2 0.2 3.9 5.7 Amnh i noH^ 1 . 1 Cari.deah shrimp 1.1 73. h 33.9 Brachyuran larvae 0.5 0. 1 Pycnogon ids 0. 1 0.1 Hemipteran exoskeleton O.k k.o 0.7 Mosquito larvae 2.2 Chaetognaths 0.7 1.0 Fish eggs 1.3 0.1 Fish larvae 0.8 1 .0 0.3 Other taxa 3.0 0.1 0. 1 0.^4 Total 197.9 107.6 13^.0 7^.0

PAGE 39

30 Table 6c. Mean standing crop of zooplankton (Number/m ), March to May 1979 at each sampling site. Taxa 11 12 SI S2 Cnidarians 1 . 1 2.8 0.6 Ctenophores _ _ _ 0.01 15.7 Nematodes 282.3 15.7 17.6 34 . 0 Polychaetes ].k 1.4 0.6 1 . 1 Gastropods 0.3 0.6 0.2 5.7 B i va 1 ves 0.2 1 . 1 0.8 Ostracods 1 . 1 0.8 A. 6 1 .9 Copepod larvae 1.0 Calanoid copepods 37. 1 152.8 56.4 2 7 Cyclopoid copepods 5.0 0.3 Harpacticoid copepods 1.7 0.9 3.5 1 sopods U.J 0 ^ 1 4 Amph i pods 0.6 0.6 0.6 1 . 1 Caridean shrimp 3.0 3.3 51.9 25.8 Brachyuran larvae 0.3 1.9 43.7 2.4 Chaetognaths 3.9 0.2 Fish eggs 0.2 Fish larvae 0.2 1.7 0.6 Other taxa 0.3 1.9 0.2 0.8 Total 339.9 184.5 184.4 98.3

PAGE 40

31 Table 6d. Mean standing crop of zooplankton (Number/m ), June to August 1979 at each sampling site. Taxa 11 12 SI S2 Cnidarians — *. . — 0.3 2.7 Ctenophores — 9.1 0.2 Nematodes A. 7 21.2 27.8 Polychaetes — — 0.9 2.0 Gastropods — — 1.7 Ostracods 1.3 — h.e 3.0 Copepod larvae 0.8 — 0.2 0.2 Calanoid copepods 127.8 8.6 16.5 133.6 Cyclopoid copepods 1 . 1 0.8 0.5 Harpacticoid copepods Z.k 0.5 k.] 9.9 1 sopods 1.6 . 7.5 Amph i pods 0.2 0.3 1.3 Caridean shrimp 3.5 0.2 li».8 6i».6 Brachyuran larvae 3.3 ^.7 69.3 Hemipteran exoskeletons 1 . 1 Chaetognaths 0.5 3.8 Fish eggs 12.3 Fish larvae 1.1 0.9 Other taxa 0.03 O.it 1.1 1.8 Total 188.7 20.5 159.8 265.3

PAGE 41

32 variations in standing crops of zooplankton is lost, making the sites, in some cases, appear more similar. However, the zooplankton here are being used to interpret broad aquatic community differences in the four sites studied, and this loss of information is not considered critical . The most abundant groups found in the water column were nematodes, calanoid copepods, and caridean shrimp. Several other groups that were not as abundant but showed noticeable site and/or seasonal differences in distribution were ostracods, brachyuran larvae, and chaetognaths. Several groups such as the nematodes and harpacticoid copepods are not normally considered zooplankton, but are so considered here because, due to shallowness and windmixing, they are constantly in the water column. The exclusion of such forms would not seem appropriate when trying to reflect on the biological activity of the water column and, ultimately, how such differences might relate to fish-community structure and function. The water column at site II was dominated by nematodes, except in midsummer when large swarms of calanoid copepods appeared. At this same time caridean shrimp and brachyuran larvae were reaching their peak abundances at site SI. Site 12 was characterized by the sharp seasonality of calanoid copepods. During the spring, densities peaked, only to crash dramatically by midsummer. Midsummer in general was a period of very low plankton standing crop at 12 relative to the other sites. ' The seagrass sites were distinguished somewhat from the impoundment sites by the greater densities of caridean shrimp and brachyuran larvae and were distinguished between themselves on the seasonality

PAGE 42

33 of these same taxa. Caridean shrimp densities reached a peak at SI during the winter and spring, whereas they peaked at S2 in midsummer. Brachyuran larvae were much denser at SI than any other site, and reached a peak density during midsummer as they also did at S2. Sites 51 and S2 were also distinguished by consistent chaetognath populations. Overall, the spring was the period of peak zooplankton densities for both impoundments, while one seagrass bed peaked in spring and the other in midsummer. Macrobenthos The results of the quarterly sampling at each site are shown in Tables 7, 8, 9, and 10. The values shown in Table 11 were used to convert dry weight to joules. Nematode densities were converted to biomass using 1.46 yg/nematode (Day et al . 1973) and copepod densities were converted using 18 ug/copepod, a general value cited by Day et al . (1973). Based on average annual standing crops of energy, sites II and 52 were significantly lower than sites 12 and SI (Student's t, p < 0.01). This is also reflected in the number of major storages, here defined as taxa with average standing crops in excess of 2 kJ/m^, at each site. Diversity of storages is assumed to be indicative of the diversity of energetic pathways within the system. Sites II, S2, 12, and SI had 3, 6, 7, and 10 such major energy storages, respectively. The contributions of major taxa to the annual average standing crop are shown in Table 12. Both impoundment sites were dominated by bivalves, whereas the seagrass sites had a much larger storage in polychaetes and, in general, had greater equitability between storage compartments. Major storages unique to the two site types were

PAGE 43

34 i0) — VI • +-> I/) ''^ fO Sc > c c ns •r cu X3 c o re to >> Q. SO OJ S+J cn s<0 o o"-5 fO cu E D1 (O CD t. . £: +J > So 10 <+-"CM E 01 4-> -3 r^ t/0 -Q Hi Ol > < 3 Q. < > c 1_ o 4-1 o o >cn i_ c UJ ;o c 0) o >Ol c 1/1 c o Ol 1) c lO c 0) Q >CD U 0) c UJ 1/1 c 0) Q CI c l/> c o LA oo -T LA Ln LA CO LA LA o CN 00 o o O o o CM •~ O cvj f — \ t^ ^ — J o D CM V V OA LA V > O < — rA CM ro LA PA OO 3 o csl OO CM C CN CM c o < CM LA O — O LA CN CM o V rA cn rA LA CM OA OO o o 0. 0) o o ro -o o a C2. D O C o a; o Q. O 1/1 n3 a o a. (U Q. o LJ u tj fO E 3 t_) O • CO CM o o (TV CM vX5 cn CN CN CM PA OO CM LA crv o 13 o (T3 -o o ro ro o a TJ 3 o o > O U (TJ L. w c 1_ 4-1 3 U l/l > Q. 1/1 03 o o CD CO t/1 1-

PAGE 44

35 >5 CD c 00 Q. O so CD c o c (O 4-) (/I o c: E 3 (U +-> 00 •1 c (d 0) JO-Q O) I— +J c > c c 03 -rOl U (O ^ S+J QJ c: > >CL I— 3 io QJ S+-> D1 iro S. 3 O Cr-r-, fO O) E CI ra (U s-^ ta io t— <\J E OJ •r^ 00 CO OJ "3 OJ TO 0) > < cn I/) c o cn 1c 1/1 c 0) o (U c D C I(D J3 O 4-1 o o in C Q c c o cn in c 0) o r>LTV Lr> ^ \D — 0~\ \0 vO o CO — CM o C30 -3\£> O — CM — PA < O CM OA vO O vO cn 00 3 LA LA vO C . LA VO -3vO PA CM •jr PA 00 o cn vD r00 PA LA 00 LA -3CO O PA o PA LA -3-3cn o o C CM PA PA CM , vO CO CM cn CM PA vO CM CM LA CO vD PA PA CM -3cn vO CO -3-3CM PA o PA CM cn PA VO 00 cn LA CM LA LA PA LA CM o O lA cn vO CM vO -3vO VO O LA CM PA PA CM V -3oo CM OO -3vO O cn CM CM LA vO cn -3O PA PA CM o V VO CO cn PA vD CM LA PA o cn vO CO -3PA PA r-PA cn 00 LA PA cn LA -3-3vO O -300 CM PA cn o LA CM CO 00 PA LA oo OO OA PA CM PA cn vO cn vo cn -3" vD PA LA — — CM vO PA PA -3o o V rM CA — o CO CO vO PA vD — PA V o m u >o a. TO o o cn TO •D O a JZ Q. E < TO o O Cl TO U o TO Q) O TO o TO C TO TO TO TJ TO c TO 0 T5 O 0) u O Q. o TO Q. tt) TO u O a E in o 3 in (-> O O TO o O Q. O V. 4-' in TO C2 TO E (1) TO TO TO C XI 3 > O 4J O >lc TO 4-' TO (D D > TO P E C 5 0) CO a. z z l/> JCO o CM VD PA CO lA PA CO (TV PA PA LA CM Pvl LA CM LA vO 00 -3CO LA in TO o

PAGE 45

36 >> 1. c (/) Q. O So ai c o +-> to T3 c to E :3 1/1 cu •f— • -M to •1a; (/) +-> c (O QJ S"O -Q I— +J c > fO -1 CD T3 ^!= O fd to >5 Q. 1— 3 so 0) s+-> ai sm s3 o cr-r-, ai E cn n3 oj S^ OJ 4J > o in t|_ OTCM E ^ •rjk: OJ (TJ > < >3 Q. < >c c 0) c to c 0) o >u c >i_ OJ C u o lO o c c 0) o > cn u D c LU to c 0) o 03 X o OO LA LA 00 CN LA OO o D vO o LA CA OO o o o o LA o Jo Ol O . _ rr\ CN O rA O OO O rA LA o CN o CN L. — V rA LA 0) -3> -T < -3rA cri 00 CN vO r>* CM LA LA rA C CN -T C O o O rA oo fA rA o o LA o CN CO rA , o o CN CN o o o cr\ o o no V CN UA LA vO Ln cn OA rA 1 — PA o -J" rA CN rA OO rA CN QO o o CN o rA o oc LA LA o O O -T o ND c 0 a. •J T3 3 > 5i 03 D 03 U OJ 0 "5. ec UP 0 /I do uin ^ 01 3 > Qo < Q (— (_> O o 1) V TJ a. 03 0) c 03 03 — 3 3 O (J C 2 3 5 Z c/1 03

PAGE 46

37 a) L. 0) > < OI c OO Ln o -3vO LTV -a-T c 1 — OO -3(U -3u < C 1_ 0) O 4-) o o > u V c LU c Ol u c 1/1 c o c 1/1 c o > Ol L. c LU 1/1 c o X in — CN so CM -3" CM CO OO vO -3-3vO OO -3Ln {M O O (-^ vO O O O O o O O o — < -3" Cr> (TJ vO « /I ><_> X. o X o 03 -3 0 n -3 o 03 > 03 > U1 <0 OJ a. 03 1) C V 5 -2 o 5 3 (J 3 1/1 OJ 0

PAGE 47

38 1 Table 11. The values and authorities cited used to covert standing crops on a dry weight basis to standing crops on an energy basis, for the benthic invertebrate groups common in the impoundments and seagrass beds. Taxa Conversion Factor \\j / Illy u 1 y WL / Reference Notes Po 1 vchaeta '>0 79 3 0 1 i gochaeta 1 R 09 5 Amph i poda T C C ] 1 P • P 1 3 V W u \J CJ 3 Tana i dacea 14.62 5 1 sopod value 1 soDoda 5 uasLi \J\J\J\jo 1 / . 0 1 3 U I vol V 1 o . Uo 1 1 P 1 a tyhe I m i n t hes 27 (T; • up 1 S i puncu 1 a 1 uumacea 15.62 Nemert i nea Oph i uro i dea 20. Oi* 5.71 1 3 average of Oligochaeta and Platyhelminthes Hydroidea 12.08 1 Nematoda 18.01 2 Ostracoda 15.62 i» Cumacea value Mys i dacea 15.62 i» Cumacea value Copepoda 4 1 Cummins and Wuycheck (1971) 2 Day et al. (1973) 3 Thayer et al . (1973) h Blaber (1979) 5 Whitfield (1980)

PAGE 48

39 Table 12. Percentage of the average annual standing crop of energy for major benthic invertebrate groups at each site. Taxa 11 12 SI Pol ychaeta 5 37 60 0] igochaeta k 2 Amph i poda 6 Decapoda 2 Oph i uroi dea 15 6 Gastropoda 36 2 3.1 8 B i va 1 V i a 57 79 13 18 S i puncul a 2

PAGE 49

40 1 decapods and amphipods in the impoundments and brittle stars and sipunculids in the seagrass beds. Two subgroups, II -S2 and I2-S1 , which departed from the original habitat groups 11-12 and S1-S2, appeared based on average annual standing crop and on standing crop of molluscs. Site II had a higher percentage of bivalves than 12, but a lower percentage of gastropods. The same was true for S2 as compared to SI. Sites 12 and SI are, therefore, distinctive from their comparison sites II and S2, respectively, for two reasons. First, they have higher standing crops and secondly they have a higher bivalve to gastropod ratio than their comparison sites. Comparing the four sites seasonally, the most distinctive feature is that each site appears to operate on a different schedule of maximum and minimum standing crops of energy. Site II is bimodal with peaks in fall and spring, 12 peaks in fall, SI in winter, and 52 in the summer. Thus, the impoundments reached their peak standing crops in the fall and spring, v/hile the seagrass beds peaked in winter and summer. The magnitude of energy storage compartments and total standing crop, of course, are only structural comparisons of the macrobenthos, and do not reflect functional characteristics of the bottom communities. Therefore, significant structural differences found between sites and habitat types do not necessarily reflect differences in the rate of energy transfers within the benthic community. Epibenthic Invertebrates The dominant epibenthic invertebrates were caridean shrimp, primarily Hippolyte pleuracanthus . Palaemonetes intermedius , and

PAGE 50

41 to o o a. o 0) o o> S19 o o u O CM £1 a. o su D1 C o 4-> to -o c c 1/1 c V a > i_ D C UJ in c 0) o o> u 0) c 1/1 c D o CTi 00 O oo crv OO -3OO -3" OO CM o CM o o CM O O in o V CM E 3 c o CO CM -l-> to c a (T3 . 3 -»-> I/) c Q o c rj o V a l/l 0) c 0) (/I D TJ Q. fO (/) l/l
PAGE 51

' 42 Perid imenes americanus ; penaeid shrimp, Penaeus duorarum and Penaeus aztecus ; and the blue crab, Cal 1 inectes sapidus . Based on Odum (1971), these three groups represent a broad trophic spectrum and therefore should be functionally grouped together for very broad general comparisons, as done here to highlight the fate of net primary production in each system and to compare habitats and community structure. Several other species were collected, but in very low numbers (i.e. the mud crab, Neopanope packardii ; the spider crab, Libinia dubia ; the hermit crab, Pagurus bonairensis ; and the snapping shrimp, Al pheus heterochael is ). At each site, caridean shrimp were the numerically dominant group (Table 13). However, based on average energy content, blue crab and penaeid shrimp were dominant at sites SI and S2, respectively. In comparing the yearly totals for each site, II had distinctively lower standing crops of the major epibenthic invertebrates than the other three sites. Site 12 was dominated by the influence of caridean shrimp, while SI and S2 had more equitable distributions of standing crops among all three groups. Fish Community Structure Species Composition and Seasonality A total of 44 fish species were found in the study (see Tables 14, 15, 16, and 17). Fourteen species were found in the impoundments, but none was restricted to these sites. Between the tv/o impoundment sites, the difference in the species list is due to rare species. This is also the case when comparing the two seagrass beds; some relatively rare species were unique to one site or the other.

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43

PAGE 54

45

PAGE 55

46

PAGE 56

47

PAGE 57

48

PAGE 58

49

PAGE 59

50 i

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51 The impoundments were characterized by high densities of several species of atheriniform fishes, as well as the clown goby, Microgobius gulosus , all of which were considered yearly residents. Site II showed a slight decrease in total species number during the winter which was quickly made up in the spring, beginning in April. Site 12 did not experience a winter exodus, as did II. Three of the four seasonally occurring species at 12 v/ere found between October and January. The only commercial or sport fish collected was a solitary Mugil cephalus at site 12 in April. The yearly residents of the seagrass beds included the atheriniforms and the goby of the impoundments, plus the gulf pipefish, Syngnathus scovelli , and the code goby, Gobiosoma robustum . Juveniles of species of the families Sciaenidae, Gerreidae, and Sparidae were also dominant community members on a more seasonal basis. The seasonality of both density and energetic standing crop (Tables 18 and 19) at the seagrass sites SI and 32 and the impoundment site 12 appeared to be on a regular cycle of winter minima and summer maxima. Site II, in contrast, had three depressions in both density and energetic standing crop, October, March, and June. The average densities and standing crops of energy at the impounded marsh sites were significantly higher (Student's t, p < 0.05) than at the seagrass sites. Differences between the two impoundments and differences between the two seagrass beds were not significant. The sheepshead minnow, Cyprinodon variegatus , was by far the dominant member of the impoundment communities studied in terms of average density and average standing crop of energy (Table 20). The same atheriniform fish are shared dominants between sites II and 12,

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52 Table 18. Total fish densities at each site. Density (#/m2) Year S Month II 12 SI S2 1978 July 22.70 5.29 3.37 August 12.59 24.09 0.63 3.76 September 31.56 10.89 2.28 4.57 Octobe r 6.10 9.16 2.26 4.00 November 11.^*8 8.73 1.14 3.98 December 13.61 3.28 0.84 0.90 1979 January 1 1 .23 3.3't 2.42 1.64 Februrary 17.65 11.11 2.32 6.81 March i*.36 18.85 1.19 1 .06 April 16.20 17.76 1.07 0.82 May IA.25 38.13 2.91 2.00 June 7.09 57. ^49 4.14 9.40 July 1^.88 52.36 10.60 7.94 August A7.19 101 .66 13.62 7.32 Mean MM 27.^5 3.62 7.32

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53 Table 19. Fish standing crops of energy (joules/m^) at each site. Year £ Mnnth T9 C 1 S2 1978 Julv 1 7 *7 ^ "7 1 7737 9735 Ai in 1 1^ f >uu/z 259'<9 111 onci iioit> 5577 15993 uc tODc r oUo 3 QCr\Q odOo 9875 iiU VCMlUc r Q 7 1 fi OO^D 1 093 7933 1 r o /i Z72o 0 r 0 1. 2504 1979 January 19717 5816 i«768 6654 Februrary 32538 2803A 3746 2996 March 5791 353^9 1452 I960 April 13337^ 31117 2033 1559 May 8l 03^ 52791 3614 4156 June klk]}. 99887 6374 9739 July 87057 103806 14132 9273 August 159985 194279 11637 9713 Mean (all nranths) 53672 53^01 6510 8437 Mean (Sept 78-Aug 79) 5835A 53678 5480 6870

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54 >. CTI U) 1fO (U L. c V UJ > < uO o a o 0) i_ 1 CJ fO 4-1 c c (U o lC (U nj Q. to 01 C30 CO CM C 0) < 0) cn 4-1 c u l_ (U a. CNI -3CM — . LA rA — o CM oo LA LA CT^ rA vO -3-3O — ro in 13 0) 3 E 1/1 3 Ol c IT) (13 1/1 3 0) O ~ C C a> U 4-J Uru >> o 1/1 o IT) ui_ C i/i 1_ noi c o 113 o> ^ La.
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55 but 12 has a much more equitable distribution of standing crops of individuals and energy. The tm most abundant species across all habitats were the rainwater killifish, Lucania parva , and the silverside, Menidia peninsulae . Within the seagrass beds, the two gobies and the pipefish made up a large fraction of the average number of individuals per month, but, in terms of standing crops of energy, the more seasonal pinfish, Lagodon rhomboides , and silver perch, Bairdiella chrysoura , were much more significant. Environmental Correlations The correlations (Spearman Rank) of numbers of fish species, fish density, and fish standing crops of energy to salinity, median water temperature, and standing crops of seagrass (SI and S2 only) are given in Table 21, The strongest correlations existed between fish standing crops in units of energy and median water temperature, especially at sites 12 and 52. Correlations of community structure to salinity show a contrasting pattern between the two impoundments. The number of fish species found each month at the low salinity site (II) was positively correlated with salinity. Site 12 had much higher average salinities and the number of fish species found each month was negatively correlated with salinity. Standing crop of energy, however, had a significant (a = 0.05) positive correlation to salinity at 12, while almost no correlation existed between them at site II. The seagrass beds had no significant correlations between fish community structure and salinity. Sites SI and S2 showed contrasting correlations between fish community structure and seagrass standing crop. Site S2 had significant

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56 +j •r* t/1 C" II (J sQJ t-> tn ro CO c o OJ o V +J OJ LO CL c 3 -a 4-> E c n3 ro O 4-> C 00 ro U •p— +-> c i/l CD C +J (1) (/) a 41 O 10 * fO II CO QJ to CO sSO) o •M <+u n3 o fO 1. QJ o ra S3: x: 13 u *-> c: (T3 to S_ Q. :3 E +J (D O +J 4-> OJ OTCSJ S_ I— CO 4+-> A II O c J3 IT) O •rST3 Q. o (0 CU q: E +J o c: V jg >> Q. S_ '1 — u (T3 c +J 0) CO an CO >^ (J c cr •r— o o 4+-> •r— 4-) 4-) n3 o fO en E •r— OI QJ 1/1 SS_ 1 lSo r— o K (_) 2 o K CM to A to to >J3 TO 4J 0 I. O) in a. TO c 0) (1) to a 0) 4) *j L. TO i-i TO c L. TO (1) Ol T3 E (U u 1J3 o 4-1 c TO t/) O 00 \D o O o o O un o cs -3o o O O 00 -ao I -3— CO — 00 CN 00 -3o o o o o o O o -3-3OO \S\ 00 — O \D -3vO o o o O o o -!: •K ^; oo CO o — \o \0 o o O CM CM O o o o o o O O O o o o o CM n-\ OO CM OO LPi -3o O O O O O o o O O LA o CM CM CO o CM o CM vD -3" 00 cn CO CM r~. o CM CM o CNI CM ro VO CsJ O o o o o o o o O O lO TO L. .— 3 I*-! 0) U 4-1 3 (J U TO 4J L. I/) TO 0) to CO (SI o CM OO O o -3ro o o o o O O ro O LA CM CO ro CM CO O O O O O O to 0) O 0) Q. CO to — >lO c 0) o to E 3 >. O) O) 1. 1. 0) 10 (U c Q) c LU 1 O LU 1 a (U Q. 0 a 0 u CO 1o ai to cn c >c u. 4-< T3 o C uto c TO O c TO •i-J C71 L. 10 to (1) c 0) LU u 1 O (1) Q. 0) Q. O Q. OO Cr 1/1 j:: to Ol to >c Ll. 4-1 XI Ll. uto c ti0 en TO 4-1 0 I. CO L. 0) a) J3 x: E to to E D Ll. Z > to c o 01 CM CO >O) L. 0) c LU I o DI C XI c TO JO to

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57 (a = 0.05) positive correlations of species number and standing crop of energy to seagrass standing crop. The correlation of fish density to seagrass was also highly positive, though not significant, at S2. In contrast, site SI had very weak positive correlations for all three structural characteristics to seagrass standing crop. Energy Contents The energy contents of juvenile and adult age classes (Table 22) are significantly site specific (Duncan's Multiple Range Test~"DMRT," a = 0.05). Rather than a continuous gradient of energy content values between the sites, all the sites had significantly different energy contents for juveniles, resulting in a discontinuous gradient of communities. The only overlap of communities was found between the adult fishes in the seagrass beds. The juvenile and adult age. classes of the impoundments were not significantly different from each other (DMRT, a = 0.05), but in both cases, as shown in Table 22, were higher in energy content than similar age classes from the seagrass beds. Site SI was the only site where the two age classes were significantly different in energy content (DMRT, a = 0.05); in that case the average adult had a higher energy content per mg ash-free dry weight than did the average juvenile. The differences in mean energy content for species at each site are presented in Table 23. Of the two dominants, Menidia peninsulae and Lucania ^arva, Lucania demonstrated a significantly greater energy content per gram of ash-free dry weight at sites II, 12, and S2 (DMRT, a = 0.05). The two seasonal dominants in the grassbeds, Lagodon rhomboides and Bairdiella chrysoura, are also significantly

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58 Table 22. Mean energy content of juveniles and adults of all species at each site; means which are not significantly different from each other are connected by a horizontal bar, Duncan's Multiple Range Test, a = 0.05. Juven i 1 es Adults N 113 Bk 111 79 J/mg ash-free dry wt 23.6A6 23.953 2^4.7^3 25.124 Site SI S2 12 II N 77 82 ]5h 101 J/mg ash-free dry wt 2^.086 2^.117 2k.k88 25.299 Site S2 SI 12 II

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59 Table 23a. Mean energy content of common species at site 11; means which are not significantly different from each other are connected by a vertical bar, Duncan's Multiple Range Test, a = 0.05, N--sample size. Species Energy Content (j/mg ash-free dry wt) N Lucania parva 25.655 8 Gambusia affinis ISAjl 3 Cyprinodon variegatus 25.808 117 Poecilia latipinna 25.052 18 Henidia beryl 1 i na 2^.839 • 25 Henidia peninsulae 2A.820 20

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60 Table 23b. Mean energy content of common species at site 12; means which are not significantly different from each other are connected by a vertical bar, Duncan's flultiple Range Test, a = 0.05, N--sample size. Species Energy Content (j/mg ash-free dry wt) N Anchoa mi tch i 1 1 i 25.8A0 4 Gambusia affinis 25.309 49 Lucania parva 25.122 51 Poec ilia I at i p i nna 2k. 80k 29 Microgobius gulosus 24.375 1 1 Men i d i a bery 1 1 i na 2h.2k7 15 Cyprinodon variegatus 24.203 k2 Fundulus grandis 23.852 30 Menidia peninsulae 23.769 39

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61 Table 23c. Mean energy content of common species at site SI; means which are not significantly different from each other are connected by a vertical bar, Duncan's Multiple Range Test, a = 0.05, N--sample size. Species Energy Content (j/mg ash-free dry wt) N Cyprinodon variegatus 25.531 2 Lagodon rhomboides 2i».908 20 Haemulon sciurus 24.277 8 Microgobius gulosus 18 Gobiosoma robustum 2k. 22] 7 Syngnathus scovel 1 i 23.891 15 Anchoa mi tch i 1 I i 23.787 5 Leiostomus xanthurus 23.763 3 Eucinostomus (juveniles) 23.756 6 Lucania parva 23.683 • 36 01 i gopl i tes saurus 23.623 3 Menidia peninsulae 23.598 Cynoscion nebulosus 23.303 k Men id ia (juven i les) 23.078 5 Ba i rdiel la chrysoura 22.878 12 Mugil cephalus 22,877 1

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62 Table 23d. Mean energy content of common species at site S2; means which are not significantly different from each other are connected by a vertical bar, Duncan's Multiple Range Test, a = 0.05, N--sample size. Species Energy Content (j/mg ash-free dry wt) N Lucania parva 24.953 53 Lagodon rhomboides 2^4.758 17 Fundulus grandis 2^4.539 3 Cyprinodon variegatus 2^.249 i» Archosargus probatocepha 1 us 24.173 3 Microgobius gulosus 23.879 9 Menidia peninsulae 23.802 37 Syngnathus scovel 1 i 23.705 ' 21 Floridichthys carpio 23.6^3 2 Bairdiel la chrysoura 23.326 12 Paral ichthys albigutta 22.667 3

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63 (DMRT, a = 0.05) different in their average energy content per gram of ash-free dry weight in the two grassbeds. Within the impoundments and S2, Cyprinodon variegatus drops to significantly lower energy content per gram of ash-free dry weight than Gambusia af finis and Lucania parva . Also, at 12 the species with higher energy contents appear as more discrete groups than in II and S2 and, to some degree, SI. Fish Community Function Monthly respiration and production for the major fish species in each community are shown in Tables 24, 25, 26, and 27. Respiration was approximately one order of magnitude greater in the impounded marsh sites (II and 12) than in the seagrass sites (SI and S2). Differences in annual production were even more dramatic, with the impoundments (n and 12) roughly 22 and 15 times more productive, respectively, than the seagrass beds. The impoundment sites were most productive during the months of April and June, whereas the first large pulses of production occurred in the seagrass beds during June and July. All four sites experienced large respiratory losses during July and August. A second staggered seasonal pulse of production was noticeable in the fall, with II peaking in September, 12 and SI delayed until October, and S2 with approximately 39% of its total production occurring during October and November. The bimodal production process of fishes in the seagrass beds is consistent with earlier studies on the shallow water fish communities of the northern Indian River (School ey 1977) showing a spring/fall recruitment sequence for the shallow seagrass bed communities.

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64 C -o 0 c •1fO 4> fO c so •r•(— Q. +-> l/l (O OJ S5-11 Q. a: iM 5E s\ o -O 4C I— •rro +-> 1/5 O OJ •-> :3 ^^^ — n3 fO > 3 C c c O fO •r-t-> to u :3 OJ (/) •O CU O -r>S(/7 O Q. O) O) Q. 0) ^ (/) > +-> •rSZ +-> 4U •ro rO (/) 0) O O) Q. CD >, T3 +J C C "O fC OJ O) O +-> C i3 o a; J2 •1CL-i•M I i(O 5r5 +-) sc •I" O Q. C U to o Q. O •rI S1/1 a. Q. O) t 5

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65 c -a 0 c •1ra +J >T3 C io •r-rCL4J m fo OJ Si. •>1 a. a: m O) • sE S— o -3 4C r— rca to O cu -!-> fO > nu c c o fO +-> to u 3 OJ to +-> cu o •r— 5to o Q. cu OJ CL to > +J M Mo o (0 to (U O , X3 t-> C C XJ (13 CD cu O 4-> C So QJ -Q Q. •r-(-) s_ ro -l-> Sc o Q. o 10 o 0) •rc: s_ -t-> o o CM r3 •4-) 1 — 1 o O o 13 O) s_ X5 +-> Q. O •r1 S00 Q. Q. CM (U jQ ."J u~» rs( oo fSJ O — — -J rs( \D Lf> J— — C — Jr>o (SI c vi: — vO o — S — ^1

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o o

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67 J OO c o o c rO +J ns C i. o •r•p— Q. +-> V) (0 (U t. sCL (/I (U NJ So c •rn +-> (/) o OJ u 3 (0 (tJ > C C o rO -t-> t/1 u 0) 1/1 1-J QJ o •f— Sl/l (J Q. QJ l-J •r^ 4-) O •rO fO (/> QJ O QJ QCD >, (O -Q -o -P c c "O 03 QJ QJ O +-> C S3 o QJ X5 'rCL •r+J SIB &5 4J &. c o Q. c o (/I o CU •r— c s+-> o o •r— I — • 3 +-> oo o o o 3 QJ s4-> Q. o •p— 1 S00 Q. CL I -T 00 o — o — — CC U" U-1 — —

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69 o c •rta (0 c so (/) ns nu c o (0 •r+-> U 3 to T3 +-> 03 O Sto U Q. 0) Q. 0) ^ > ^ 4-> 4u •r~ O ro to , ra "O +-> C c o (O o (J CNJ 3 +-> OO T3 o o 3 Q. O it/1 Q. Q. — o — CVJ
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70

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71 I Annual production and respiration within site II was dominated by Cyprinodon variegatus . The next two dominant species are possibly more ! noteworthy for their ratio of production to respiration than the ! absolute quantity of either. Menidia beryl! ina contributed a disproportionately higher share of production to total community production for its average standing crop and respiratory demands, while the Poecilia latipinna population produced very little net production relative to its large metabolic losses within the system. At site 12, the impoundment canal, production and respiratory losses were more equitably distributed among six species than they were at II. The two dominant species were Lucania parva and f-ienidia peninsulae . The Lucania parva population had a large portion of its annual production in August, as did the Gambusia affinis population. Respectively, they produced 44% and 40% of their yearly population productions during the warm month of August at site 12. Lucania parva is also a functionally dominant species in the seagrass beds. However, the population's contribution to annual production appears less significant and, at SI, was a minor part of total community production. Two species that were important in their contributions to production within the seagrass beds were Bairdiel la chrysoura and Microgobius gulosus . The former was a seasonal recruit from June through September, while the latter was a continual resident of both seagrass beds. The same type of disproportional ity in rates of production and respiration found for two populations at site 11 was also found within the seagrass beds. However, in this case it is intraspecific for the species Menidia peninsulae , a dominant functional member of both seagrass beds. Menidia peninsulae made noticeably I

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72 different contributions to the annual production and respiratory balance within each community. At site SI the population's ratio of production to respiration is 0.4, while at site S2 the same ratio is 0.08.

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DISCUSSION Abiotic Factors The controlling physical factor within the systems studied is the variation in solar radiation. This variation produces a dynamic balance among the influences of direct solar heating, evaporation, and precipitation in generating the daily physical -chemical characteristics of the aquatic habitats studied. During the winter, temperature depression is correlated with reductions in the structure and function of the fish communities. In the seagrass beds Jones et al. (1975) suggested a two season pattern for the resident fishes. During the warm/wet season they hypothesized an inverse relationship between rainfall, which led to lower salinities, and the number of species occupying the seagrass beds. The second response hypothesized was that during the cold/dry season, even though rainfall was decreasing and salinity rising, the drop in water temperature resulted in a further decline in the number of fish species. Schooley (1977) demonstrated a bimodality in density and diversity in the shallow water habitats of the northern Indian River and Mosquito Lagoon. Because of their shallowness, these habitats may reach zones of appreciable thermal stress during midsunrier and midwinter, affecting both residents and seasonal recruits. Both seagrass beds had slight late-summer depressions in density followed by higher levels in the fall. 73

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74 Within the impoundment 12 the correlations of both salinity and temperature to fish community structural characteristics are unclear due to the influence of marsh morphology. Small changes in water level can have vast surface area effects within the impounded marshes (Snelson 1976). With heavy rainfall, the total marsh area may increase dramatically during the cooler months, as it did at 12 during January. Therefore, subsequent density measurements are lowered as a function of the proximity of newly covered marsh for dispersal of the standing crop. Similarly, during the warmer dry months densities would increase as water evaporated from these shallows. This could lead to a positive correlation of standing crop to salinity. This theory may explain the correlations at 12, but density was not significantly (a = 0.05) correlated with mid-channel depth at this site. The significance of this shift in ecological density at 12 remains. to be investigated. Similar phenomena are not believed significant at the other three sites. Day et al , (1973) found temporal patterns within a Louisiana salt marsh and shallow estuarine system to be controlled by temperature, as did Adams (1976a) in a North Carolina Zostera bed. Subrahmanyam and Drake (1975) found no correlation of abundance (numerical or biomass) with seasonal temperatures or salinities in two north Florida salt marshes. However, several species groups did show significant correlations to either temperature or salinity. The seasonal succession in the recruitment of the juveniles of several species found in earlier studies of seagrass beds (Jones et al . 1975, Schooley 1977) was also observed. This same sort of recruitment sequence, which would be expected for a marsh (Subrahmanyam and Drake

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75 1975), did not, of course, occur within these impounded marshes. Some minor recruitment may occur at water pumping stations (Jack Salmela, personal communication) when water levels are being maintained in the impoundments by the pumping of water in from the open lagoon. Snelson (1976) concluded that the major factors controlling the spatial distribution of fishes in permanent impoundments were salinity and vegetative cover. Both salinity and vegetative cover differed between the two impoundment sites studies; however, salinity differences between 11 and 12 would not appear to be physiologically significant to the dominant atheriniform fishes. Snelson (1976) and Gilmore (1977) both characterized the impoundments of the Indian River area as stressed environments to which only a small group of species are adapted. During the period of this study the two impoundment sites did not appear any more "stressed" in terms of fluctuations of salinity or temperature than did the shallow seagrass beds. The obvious difference is the open versus closed nature of the two systems. Species within the impoundments do not have a temperature and/or salinity refugium to which they can retreat when conditions become too stressful for that particular species. It appears, then, that knowledge concerning factors other than environmental fluctuations, such as the degree of potential recruitment and the flushing of detritus, may also be important to our understanding of the differences between marsh and seagrass fish communities. Gilmore (1977) listed 26 species that have been found in the impoundments of the Indian River system. All of them were also found in the open estuary. Snelson (1976) found that brackish impoundments of Merritt Island support about ten species, the dominant six in all

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76 cases being the same that dominated sites II and 12. In the grass flats of the Indian River, a total of 208 fish species have been collected (Gilmore 1977), 87% of which are found primarily as juveniles. Approximately 30% of species collected in seagrass beds SI and S2 were found only as juveniles, and another 21% were found predominantly as juveniles. The dominant species collected in this study were different than those found to be the dominant grass flat species by Jones et al . (1975). Jones et al. (1975), using a large sweep seine (61 m) to cover an area of 1,161 m , described the residents of the grassbeds in the southern portion of the Indian River as being dominated by Eucinostomus gula , Eucinostomus argenteus , Diapterus auratus , Lagodon rhomboides , and Bairdiella chrysoura . The species found to structurally and functionally dominate the seagrass beds in this study were smaller demersal and bottom dwelling forms. The sampling techniques used in this study are biased towards these species, just as the technique used by Jones et al. (1975) was biased against these same species (Gilmore et al . 1976). The techniques used here are assumed to be biased, as are all fish collecting techniques, but are believed to realistically reflect fish standing crops of density and energy within the seagrass beds (Gilmore et al. 1976). Biotic Factors The most important biotic factor controlling communities within Indian River seagrass beds is seasonal change in macrophyte standing crop. During the spring and early summer, the grass beds provide greater habitat complexity and strongly influence the physical.

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77 chemical, and biological processes of the entire system. In the fall the grass beds, often carpeted with diatoms, die back, producing vast amounts of detritus that show up about six weeks later with a resulting pulse of organic carbon into the sediment (Clark 1975). This seasonal pulse effect appears to be a general characteristic of seagrass-based ecosystems (Phillips 1960, Odum 1967, and Phillips 1974). Clark (1975) discussed the effects of this seasonality of detrital input on the dominant groups of benthic invertebrates within the lagoon. The density of invertebrates in both seagrass beds, SI and S2, was greatest in January, followed by July, April, and October, in that order. In Clark's (1975) study of the benthic invertebrate communities of seagrass beds, he found two peaks in density, the maximum peak being in November-December with a second in May. The seagrass beds studied here appear to operate under the same seasonal density patterns as those studied by Clark (1975). The seasonality of detritivores has an overwhelming influence on total benthic invertebrate density in the grass beds of the northern Indian River (Clark 1975). Clark (1975) pointed out that the early winter peak in density is a direct response to that growing-season's decomposing seagrass, while the early summer peak may be a response to increased availability of refractory detritus, which was not decomposable at lower winter temperatures. However, he also pointed out that the reproduction of temperate species is keyed to increasing vernal temperatures and is a factor contributing to the early summer peak in density as well. This sequence of density cycling which is keyed to detrital input and reactivation appears to dynamically link the benthic invertebrate community with the production and seasonal recruitment of fishes within the seagrass beds.

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78 Within the impoundments the pulsing, if any, of detrital input is not known. Pool et al. (1974) reported a general pattern of increased leaf fall during the rainy season for mangrove forests in south Florida. If this is true for the impoundment mangroves of the Mosquito Lagoon area, maximum leaf fall, on the average, would occur during June, July, and August. The maximum standing crops of Chara occurred in December and September at sites 11 and 12, respectively. Based on this limited information, it is speculated that the two primary detrital sources are pulsed, but not synchronously. Mangrove litter is assumed to produce a late summer pulse in finer detrital particles; winter diebacks of Chara , on the other hand, would produce a spring pulse in utilizable organic material as temperature increases speed up bacterial and meiofaunal detrital processing. The seasonality of invertebrate infaunal densities at site 12 appears to correlate with such a model of detrital pulses, since densities in fall and spring are greater than in winter and summer. This is the reverse of what was observed for density in the seagrass beds. The same pattern found for density and energetic standing crop at 12 was also found for standing crop at II. The density at 12 during the fall was less than that found during the winter. The greater than average rainfall during December may have produced greater litter production during this time. If isopod populations tracked this hypothesized pulse in detritus by increased reproduction, it would explain their numerical dominance and relatively smaller contribution to energy standing crop per individual due to a predominance of juveniles and immature individuals. The amount of detritus produced in the impoundments appears to be greater than in the seagrass beds. Unfortunately, with complete data

PAGE 88

79 from only one impoundment, the significance of the difference found is not known. Chara, which was found in dense patches in various portions of the impoundments only contributed 20% of estimated net production. The production estimate for the impoundment mangroves of site II (0.47 g-m" -d" ) is approximately of the same level as those found for mangrove scrub forests at Turkey Point in southeast Florida (Pool et al. 1974). This forest is then about 25% as productive as basin forests of southern Florida, which have greater freshwater turnover than scrub mangrove forests. Annual net production in the seagrass beds averaged 3,060 -2 -1 kJ-m .y for sites SI and S2. By comparison, using Eiseman et al.'s (1976) estimate of above ground monthly standing crop and applying the same calculations and conversions, an average of 3,065 kJ-m^-y^ was derived. Clark's (1975) estimate of monthly standing crop for. northern Indian River seagrass beds applied to this same formula yielded an estimated average annual net production of only 1,273 kj.m"^-y~^ Red and brown algae, which were not significant in the shallow grassbeds at SI and S2, did contribute to production in the deeper sites studied by Clark (1975) and Eiseman et al . (1976). Maximum minus minimum standing crop was used as an estimate of net production of algae (Steve Davis, personal communication). Net production was converted to joules based on average calorimetry values for phaeophytes and rhodophytes of 12.79 and 13.27 J/mg dry wt, respectively (Cummins and Wuycheck 1971). This would add 279 kJ-m'^.y"'' due to red algae production to the 1,273 kJ-m'^-y-^ produced by seagrass in the area studied by Clark (1975). Red algae are estimated to produce 783 kJ-m"^.y'^ and brown algae 224 kJ-m'^.y-^ for a total of 1,007 kJ-m'^.y-l in the

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80 grassbeds studied by Eiseman et al. (1976). In these two cases, estimates of net seagrass production were 3 to 4.5 times that estimated for large algae. The seagrass beds of this system are on the lower end of the range of annual production for seagrass-based ecosystems. Assuming 1 gC is equivalent to 42 kJ, production estimates in kJ-m"^-y"^ for Zostera beds were 8,943 and 5,280 in North Carolina (Adams 1976b), 24,528 in Puget Sound (Phillips 1974), and, for a Thalassia bed in the Caribbean, up to 122,540 (Thayer et al. 1975b). Production in both the impoundments and the seagrass beds is very low relative to similar systems. The reduced circulation in mangrove impoundments such as II is believed to be partially responsible for lowered mangrove production. The frequency and duration of winter freezes may also be a significant factor. Within the seagrass beds Clark (1975) speculated on four nonexclusive hypotheses for reduced production within the grass beds of the Mosquito Lagoon and northern Indian River. They v/ere 1. lack of appreciable currents, leading to localized depletion of nutrients; 2. nutrient limitation due to sediment characteristics (i.e. coarse sediments with less surface area for microbial regeneration of nutrients); 3. intolerance to low temperatures for seagrasses at the northern extent of their range; and 4. carbonate limitation. The characteristics of the entire ecosystem and specifically the fish communities are possibly then controlled by these same processes.

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81 Production \ i Total production in each system was the sum of the positive production values for each species each month. Negative production values were excluded for the summation of total production, which according to Chapman (1978) should be done if one is interested in community metabolism and estimating assimilation and production efficiencies between trophic levels. The most noticeable portion of production not taken directly into account by these calculations is production in the form of reproductive products. This is assumed to have a greater potential impact on underestimating the production at sites II and 12 which had a larger percentage of year-round residents than did the seagrass beds. The impact of this omission in the overall production estimates is not known. Total fish production within the seagrass beds was very similar, -2-1 12.95 and 13.05 kJ-m" -y" . The impoundments had much higher production levels, 281.46 and 191.75 kJ-m"^.y~^ The seagrass bed, though similar in overall production levels, were rather dissimilar in the relative contribution to site production by year round residents of the grassbed and seasonal recruits, which were predominantly juveniles. At site SI the seasonal recruits produced 42% of the yearly total production, whereas at S2 they only contributed 17%. The diurnal resident Anchoa mitchilli accounted for 3% of the yearly production at site SI while at S2 it contributed approximately 0.1%. There are few comparative studies of finfish production in marine systems. Clarke (1946), based on commercial landings for George's Banks, estimated a harvest production of 0.15-0.73 g dry wt-m'^-y'^

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82 He estimated net production as possibly twice this, or 0.30-2.46 -2 -1 g dry wt-m .y . Merriman and Warfel (1948) estimated annual production for fishes in Block Island Sound to be 1.1-2.2 g dry wt.m"^.y"\ Harvey (1950) found the production for pelagic and demersal fish in the English Channel at approximately 1 g dry wt-m'^.y"^; Hellier (1962), at Laguna Madre in Texas, estimated a production of approxi-2 -1 mately 3.1 g dry wt-m .y for the four dominant species; Day et al. (1973), for a marsh-estuarine system in Louisiana, estimated production 2 -1 at 21.8 g dry wt-m -y ; Adams (1976b), in North Carolina seagrass beds, estimated production at 21.7 kcal.m"^.y~^ i'^^.Sg dry wt-m'^-y"^). Assuming 19.85 kJ/g dry wt, the production in the seagrass beds -2 1 IS 0.65 g dry wt^m -y and in the impoundments 14.8 and 9.66 g dry -2 -1 wt.m -y . Therefore, the impounded marshes and seagrass beds in Mosquito Lagoon are on opposite ends of the range of yearly production found for marine fish communities. Production in temperate lentic freshwater fishes has ranged up -2 -1 to 40 g dry wt-m -y . In general, highly productive standing fresh waters in temperate regions produce around 15 g dry wt«m"^«y~^ (Chapman 1978). Tropical and fertilized systems can produce much higher levels. Some tropical lakes are at maximum equilibrium with yields higher than 10 g dry wt-m"^-y"^ (Welcomme 1972). Naiman (1976) reported 155.4 g dry wt-m'^.y"^ in Tecopa Bore, a desert stream in Death Valley, California. Lotic ecosystems are capable of sustaining even higher levels than lentic systems. A phenomenal 197 g dry -2 -1 wt.m .y was produced in 1967 by 10 species of fish in the River Thames (Matthews 1971 ).

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83 The ratio of production to average biomass can be a useful means of comparing similar aquatic systems as well as providing a general multiplier, which can be considered a secondary productivity function. This function would then allow production to be estimated without measuring more than average biomass (Chapman 1978). The seagrass beds, SI and S2, had P/B ratios of 2.36 and 1.90, respectively. The impounded marsh sites, II and 12, had ratios of 5.24 and 3.59, respectively. Mann (1965) hypothesized that communities with P/B ratios < 1 were energy limited. If this hypothesis is true, then none of the communities studied would appear to be energy limited. Backiel (1971) found a P/B ratio of 0.62 for predatory fish in Poland, Mann (1965) found a value of 0.65 for fishes in the River Thames, and MacKinnon (1973) calculated a ratio for a large slow-growing population of American plaice as 0.4. Subsequent studies on the River Thames have given ratios of 2.85 (Burgis & Dunn 1978). Two large freshwater systems. Lake George, Uganda, and Loch Leven, Scotland, had ratios of 1.43 and 2.13, respectively (Burgis & Dunn 1978). The P/B ratio is also an expression of energy turnover within the fish community. The vast differences in total annual fish production between the seagrass beds and the impoundments are not simply a result of greater average standing crops in the impoundments but also that the impoundment fishes are turning energy over at a faster rate as shown by their respective P/B ratios. The faster turnover of II compared to 12 is due to the relatively higher turnover rate (5.3) within the Cyprinodon variegatus population at site II. At site 12 this same species had a turnover rate of 1.6. In comparing the two seagrass beds, site SI had the higher rate and was also the bed with

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84 the highest percentage of production by the juveniles of seasonal recruits to the grassbeds. Adams (1976b) found ratios of 2.85 and 2.77 for fish in North Carolina seagrass beds. He attributed these high turnovers to production by juveniles which he estimated at 79% and 84% of the total annual production for all species. High juvenile production would also appear to partially explain the very high turnover of 18.6 found by Day et al . (1973) in a productive Louisiana estuary. Respiration The seasonality of median water temperature appreciably influenced the balance of production to respiration during the year. The ratios of R/B during January at sites II, 12, SI, and S2 were 0.29, 0.18, 0.22, and 0.15, respectively. During August, the ratios at these same sites were 0.92, 0.94, 1.49, and 1.44, respectively. The annual respiratory losses at sites II, 12, SI, and S2 were 512, 655, 60, and 81 kJ-m" -y"', respectively. The ratios of total annual respiration to average biomass, in the same order, were 8.77, 12.20, 10.94, and 11.79. Day et al . (1973), without compensating for temperature, calculated the same ratio to be 13.16 for fishes in a Louisiana estuary, and Adams (1976b), who did compensate for temperature, reported a ratio of 8.88 for the fishes in a North Carolina seagrass bed. In the shallow-water habitats studied here, standing crops were positively correlated with water temperature. This was also the case in both the Louisiana and North Carolina fish communities. Therefore, the wide range of monthly respiratory energy losses within the fish community results because fish densities are greatest at the

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85 same time higher water temperatures are producing higher rates of metabolism and vice versa. Consumption Consumption is a more appropriate indication of the functional significance of the fish community in turning over energy within the aquatic ecosystem than is production per unit area because it includes production and energy losses due to respiration. A classic example of this is the work of Davis and Warren (1965) who studied trophic relationships of cottids in an experimental stream. They found that, to a point, production increased with biomass, but then it began to fall as biomass increased further. Due to the increased interaction of individuals at higher levels of fish biomass, most of the food available was used for maintenance; at lower levels of biomass more of the available food was converted to growth. The calculated annual consumption of each species at each site is presented in Tables 28, 29, 30, and 31. Total consumption per unit area within the impounded marsh was approximately an order of magnitude higher than that occurring in the seagrass beds. Within the impoundments, Cyprinodon variegatus accounted for 44% of the annual consumption. Lucania parva , Poecilia latipinna , Gambusia affinis , and Men^idia peninsulae consumed 19%, 8%, 7%, and 1% of the total, respectively. In the seagrass beds, the majority of the consumption was within the populations of Lucania parva (37%) and Menidia peninsulae (27%). The seasonal recruits to the seagrass beds accounting for the greatest consumption were Bairdiella chrysoura with 9% and Lagodon rhomboides with 6%. Lagodon rhomboides consumed 64% of the total

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86 energy intake in a North Carolina estuarine fish community (Adams 1976b). The fish communities are estimated to have consumed a total of 992-1,059 kJ-m" -y" in the impoundments and 91-118 kJ-m'^-y"^ in the seagrass beds. In a highly productive Louisiana estuary, the fish community consumed 1,257 kJ«m"^-y"^ (assuming 1 g dry wt = 19.7 kJ) (Day et al. 1973) and in a Bogue Sound seagrass bed approximately -2 -1 418 kJ«m -y were consumed by the fishes (Adams 1976b). System Efficiencies, Turnovers, and Budgets The ratio of respiration to consumption (R/C) is an index of the efficiency of energy dissipation within a system. The R/C ratio for each community is presented in Tables 28, 29, 30, and 31. The impoundments, n and 12, had R/C ratios of 0.52 and 0.62, while the ratios in the seagrass beds, SI and S2, were 0.66 and 0.69, respectively. The conditions in the impoundments and seagrass beds seem to span the normal range of conditions found in other fish communities. A ratio of 0.61 was found for fishes in the seagrass beds of Bogue Sound (Adams 1976b), 0.62 for an American plaice population in temperate waters (MacKinnon 1973), 0.67 for a freshwater fish community in Poland (Backiel 1971), and 0.73 for the total fish community in the River Thames (Mann 1965). Day et al . (1973), in computing the energy budget for a Louisiana estuary, assumed an assimilation efficiency of 50%, which is significantly different from the 80% assimilation assumed in this study. Therefore, his R/C of 0.24 is believed to be unreal istically low.

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87 Q. a. re c o Q. E in C o o o -l-J u 3 o o SQ. c o 'r+-> n3 S_ •r— Q. 10 (U S3 C C TO TO +-> O 00 CU !q TO c o Cl I E E 3 . 1/1 — C ^ O O c o o XI o c o Q. -5 ui — • o 0) CL LA -3O lA lA cn CO O — fNj CM o -3o — -3LTl LA LA r-. CM \D CM CM o CO cri CM CM O -3O LA PA CO — LA — — O LA LA CM LA CO CM rA — _ -3\^ CM CTl JMD CO -300 rA vO LA co -3vD vO 00 00 o J\D vD CO CM LA vD 1^ — LA CM LA LA O -3CM -3CM LA CD 0) (TJ > o o c u Q. >^ O c CD I/) 3 3 D C Z! in -Q E 03 > Q. C (TJ U 3 in 3 TO TO ID Ul C c O c 3 > W 3 Q. O c > o >4-J c in TO (U 0) 3 in J3 Q. 3 TO fO TO o 4-1 TO D o C (J cn c C u 0) c 0) 0) O >^ 3: Q. lO c 3 E E O <_> j: in TO O

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88 en a. a. o n. E (/) o u o c (J o o iQ. o +-> SQ. 00 sC C I O >4-1 eg CL I E E 3 . VI -3 C ^ o C I o >4-1 rg O I 3 E -o • O -) V. — a. c I O >4-) IS fD I ^ E Q. -7 10 — 0) a: CM J3 to 0) U 0) a I/) t » LA vD LA OA LA CTl \D rA CM o o o O O O O o O 1 1 LA vD O cn CM -3" CM CM o 00 1 o O o O o O o o -3CTl OA rA 00 LA o -3vO o LA CM LA OA 00 O OA vD 00 VO v£) OA OA cn — LA LA ^ CTl CM 00 00 cr\ o LA cn CTl o — LA CM — OA I CTv I OA I PA t LA O JrA PA ^ VD LA CM v£) CM CTl O o VD CA Jo LA rA vO -3CM LA cn CM LA CM LA 00 cn \D LA LA -3CM -T CM o o CM 00 CM VO -3LA CM C 00 LA vD cn cn LA CO O rA -3LA CM -3OO 00 LA 00 rA rA cn -3-aCM rA LA CM in o 4-1 (D Q. Ol U flj D in in O l_ TJ c l/l C > TO uo x: L. u4-f C 4-1 cn TO o x: S -o o in TO o ID c o in 0 3 -C 1_ lT3 XI U D. o C E c >~ 3 TO < o Lu E 3 TO TO 4-> C in 3 3 in TO C o > >11L. C TO (U 0) Q. TO E Q. X) Ql in O TO TO TO TO tn O C TD XI D TO X) (J C c C o 3 o o l/l in 3 x: 4^ TO c cn c >~ 1/1 UA 00 LA o o LA cn o CM CM LA LA vD c 3 o <_> TO 4-1 o .i i I

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89 a. -3O CM LA \0 O OO CM O O in cf\ o o -3O o -3— ir\ o o LTV LA CM CM (_J cc o CL OJ +-> o 3 in c o u a c c o •a o iQ. C o +J SQ. t/l d) SO O CO C I o a I E E 3 . W1 -5 C ^ O o >4-1 U 1 n E o -> o ^ E Q. -5 U1 — 0) 0 LA PA -3CTl OO 10 3 in O 0) c c c u ui O c >~ <_J CL E o 1/1 o o C3 c o Q. 10 10 Q. c TJ U o Q. O. 10 0) a O J3 E O sz I. c o •a O cn OJ 3 in 1_ 0) 3 3 ro 10 JZ O i-t 3 > C in 3 0 ITJ c cn o Q. X > u c in in in in 0) 3 1/1 TJ 3 Q. Q. 3 -D -C o nj O w L. cr> tJ o c T) 0 c 0 Q i_ ai > O C o a; OJ 3 L. _l — j 3: x. 1/1 m m I. O c 3 o in ft! o

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90 a. 1 1 oo 1 oo oo (TV 1 o ro 1 o 1 1 -31 o 1 o — 1 1 o O 1 o 1 O 1 d 1 1 o 1 1 O O 1 1 o o LA o LTV o -ao -3o CO O o vD CO oo lA oo oo oo LA vD OO oo O o o o O o o o o O o O O o o CM to -(-> c o 4-) a. c o o -o c: fT3 o (J o Q. o <0 Q. sC "3 C I O > 4-1 N Q. I E E 3 • U1 -J C ^ o C I o > U I 3 E T3 • O -3 \C I o >> 4-» CM a -> 1/1 ~ — ' 0) cc 4-) o a; X) in 0) u 0) Q. (/I vo cr\ I LA o LA CM O O PA O O LA oo rA r-— -3rA CA O ro LA O -3LA LA OO vO rA -3CM (N OO OO CM rA PA cr» -3" PA PA oo -3o -3PA PA CA O LA CO CO PM I — I CM I CA PA PA CM 1^ M3 LA CM <7> OO Pvl CM CTl LA PA CA a. O l/l i_ 3 3 o JD (/) JD o O E > C 3 u O L. E 4-t IB c O fO Q. o 4-1 o e 0) l/l o c ra o o T5 l/l o 1/1 c o -a c I. 0 o TJ c •J J3 Ol >3 1 0 3 CO LJ LU CJ -J l/l 3 TO 13 l/l c O c 03 3 > (/I 3 a 0 cn 0 >4-J in I. C in 3 D z: 2: 0 a. l/l in 3 o < l/l L. 03

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91 In comparing this study's seagrass beds, sites SI and S2, with the impounded marsh, 11 and 12, the fishes of the impoundments appear to be using less of their consumed energy for metabolic purposes relative to production than the fish communities of the seagrass beds. One possible explanation for this is that the several species of atheriniform fishes that dominate the impoundments are well adapted to the rigors of environmental fluctuations typical for impoundments (Snelson 1976). However, as noted earlier, during this study the impoundments appeared to be subject to less stress, in terms of salinity and temperature, than were the shallow seagrass beds. Evidence that appears to support the idea that the seagrass beds are indeed physiologically more stressful than the impoundments are the R/C ratios of the two species that occur most frequently in both impounded and seagrass habitats, Lucania parva and Menidia peninsulae . Lucania parva had an average R/C ratio of 0.71 in the impoundments and 0.77 in the seagrass beds. Menidia peninsulae had an R/C ratio of 0.59 in the impoundments and 0.66 in the seagrass beds. In both cases, the seagrass bed population of each species was using more of its consumed energy for metabolic purposes than for growth. Other explanations such as increased search time for prey are possible, and probably are operating, but are not believed to be as significant as physiological stress (Adams 1976a, Cameron 1969). In discussing why the eelgrass fishes of Bogue Sound were apparently apportioning a lower percentage of consumption to respiration, Adams (1976b) discussed the "adaptation to stress" explanation above. Adams also went on to develop a second hypothesis that abundant energy supplies available within the eelgrass systems may be favorable enough to overcompensate

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92 for assumed environmental stress of the eelgrass beds. The response of the fish communities studied here would support an "excess energymetabolic compensation" hypothesis assuming environmental stresses in the impoundments and seagrass beds to be equal. A very important energetic ratio for relating two trophic levels is the ratio of production to consumption (P/C); see Tables 28, 29, 30, and 31. This ratio gives the gross production efficiency, also referred to as ecological efficiency by Slobodkin (1960). The gross production efficiencies for the fish communities at sites II, 12, SI, and S2 were 28%, 18%, 14%, and 11%, respectively. The impounded marsh conmunities are, therefore, more efficient at converting consumed energy into fish production. The range of gross production efficiencies for the functionally dominant species (consumption > 600 J-m"^-y"^) in each community were 1-55% for 11, 5-36% for 12, 1-31% for SI, and 5-43% for S2. Ricklefs (1979) listed a range of gross production efficiencies for aquatic poikilotherms from 1.5% for stream limpets feeding on algae to 32% for the freshwater fish, Megalops cyprinoides . feeding on fish. Welch (1968) gave a general range of 15-35% for gross production efficiencies in populations of aquatic consumers. For fish communities, a broad range of gross production efficiencies has also been found. Mann (1965) found the fish community of the Thames River to have a gross production efficiency of 6%, with values of 13-14% for young fish and 1-3% for fish over 4 years of age. Fish communities of seagrass beds in Bogue Sound which were dominated by juveniles had gross production efficiencies of 18-22%.

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93 Finally, we can examine the efficiency of transfers of solar energy into net fish production at each site. We can do this by examining the process as two transfers; solar to net primary (or detrital) production and detrital production to net fish production. The average yearly solar input is estimated to be 6,694 x 10^ kJ.m"^.y"\ based on a twelveyear average for Orlando, Florida, 75 km west of Mosquito Lagoon. The efficiency of transfer of incident solar radiation into detrital production at site II is 0.064%. This is calculated from 4,306 kJ-m"^.y"^ (mangrove and Chara detrital production)/6,694 x 10^ kJ.m"^.y"^ (solar input). The same method of calculation for SI and S2, using seagrass production, yields transfer efficiencies of 0.035% and 0.055%. Whittaker (1975) stated that efficiencies of 0.91% and 0.066% are representative values of ecosystems of moderately high and relatively low efficiency of capture. Both the impoundments and the seagrass beds can be considered to have low gross production efficiencies. The transfer of net detrital production into fish production was, at site II, 6.53% [281 kJ-m"^.y"^ (fish production)/4,306 kJ-m"^.y"^ (mangrove and Chara detrital production)]; at site SI, 5.39% [130 kJ.m .y (fish production)/2,413 kJ.m"^.y" (seagrass net production)]; and, at site SI, 3.53% [131 kJ-m'^-y"^ (fish production)/3,707 kJ-m"^-y"^ (seagrass production)]. The higher percentages of the predominantly herbivorous Cyprinodon variegatus and Poecilia latipinna in the impounded marsh are partially responsible for higher efficiency in the marsh as compared to the seagrass beds. However, what is most interesting is that while herbivores account for approximately 88% of all fish production at II as compared to less than 2% at SI and S2, the efficiency of II is only 22% greater than the more efficient seagrass

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94 bed. Over 87% of the fish production in the impoundment II is from direct grazing on detritus while 98% of the production in the seagrass beds is based on feeding done by the secondary consumers, one trophic level higher than the herbivore/detritivores of II. Therefore, the seagrass bed communities are very efficient, almost twice the biosphere average (Whittaker 1975), at coverting net primary production into production at the secondary consumer level. The overall efficiency of conversion of incident solar radiation to fish production is an index of ecosystem energetics which includes the effects of factors affecting photosynthesis, consumption, assimilation, respiration, and growth processes at all trophic levels. This index can be used to compare a variety of aquatic systems. This ratio for each community studied here is 0.0042% for II, 0.0029% for 12, 0.00019% for SI, and 0.00020% for S2. When the values found for the percentage of total solar energy being fixed and finally converted into fish production are compared to other aquatic systems, the seagrass beds, SI and S2, are near the median while the impoundments are very high relative to other natural systems. Using the fish production calculated by Adams (1976b) for the seagrass beds of Bogue Sound and assuming a total solar input of 3 -2-1 5,862 X 10 kJ-m -y (Odum 1971:42), the conversion efficiency is 0.0016% of total solar input. Bardach (1959) found a value of 0.0014% for tertiary consumers on a Bermuda reef, Hayne and Ball (1956) calculated an efficiency of 0.0014% for the fish community in a small Michigan pond. Burgis and Dunn (1978) presented efficiencies for Lake George, Uganda, and Loch Leven, Scotland, which when adjusted to total solar input yield efficiencies of 0.00064% and 0.00013%, respectively.

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95 Clarke (1946) estimated an efficiency of conversion of solar radiation into net fish production of 0.00005-0.00025% for the commercially exploited fish of Georges Banks. As developed earlier, one possible explanation for why the impoundments appear so efficient at converting solar energy to fish production, as compared to the seagrass beds of SI and S2 and to other aquatic systems, is the higher percentage of production by lower trophic levels in the marsh. In Bardach's (1959) Bermuda reef study, the efficiency calculated of 0.0014% was for fish feeding at two trophic levels above where most of the production took place in the fish community at II. However, impoundment canal site 12 had most of its production by primary carnivores and is therefore trophically more comparable to more of the references cited than 11. In general, the impoundments are two to three times as efficient as the most efficient system cited. The seagrass beds of Mosquito Lagoon are utilizing solar energy at approximately 5-10% the levels found in the impoundments. The communities in seagrass beds at SI and S2 are also only 10-15% as efficient in this energy transfer as were the seagrass bed communities in North Carolina (Adams 1976a,b). If we examine this last comparison closely we find that much of the difference in the two seagrass bed systems is due to a much lower efficiency in the transfer of incident solar radiation to net primary production in the Mosquito Lagoon seagrass beds. This efficiency (seagrass production/solar input) was 0.036% at SI and 0.055% at S2. Adams (1976b) estimated the annual net primary production of the two ^QStera beds where his study was done at 5,280 kJ/m^ and 8,943 kJ/m^. If we again assume a total solar input of approximately 5,860 x

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96 3 -2-1 10 kJ«m 'y for the Bogue Sound area, the Zostera beds had efficiencies of 0.09% and 0.15% in converting incident solar energy to net primary production. This is a range of approximately three times that found in the Mosquito Lagoon seagrass beds. The functional role of the fish communities in the flow of energy within both the marshes and seagrass beds of the Mosquito Lagoon area is significant due to the percentage of net primary production processed by the fish communities. However, the marshes and seagrass beds differ significantly in community structure and the magnitude of their energy flows. A great deal of future research is required within these marshes and seagrass beds to complete the functional comparisons begun here. The areas of highest priority would be to determine the yearly variability in production, the variability in diets of the major species, the degree of internal cycling within the benthic invertebrate and fish cormiunities, the contributions of phytoplankton and zooplankton to energy flow, and the utilization of high marsh after heavy rains. The rationale for the original impounding in Indian River was to control the hordes of mosquitos that would affect human health and economic development of the area. The benefits from mosquito control achieved by impounding can be put into economic terms with dollar values assigned to the decreased health care costs and increased development brought to the area. The negative aspects of impounding must also be considered. The impact of the complete isolation of high marsh from the lagoon reduces the potential production of commercial and sport fisheries and has a negative impact on these industries. This impact must be translated into economic terms. Then, new cost/ benefit ratios can be generated and used to evaluate present and future mosquito control strategies.

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97 Fish Community Summary 1. A total of 44 species of fishes were found in the seagrass beds, 14 of which were also found in the impoundments. No species were found solely in the impounded marsh, and none of the commercial or sport fishes found in the seagrass beds were common in the impoundments. 2. The seagrass bed communities were dramatically different in structure and function from the impounded marsh communities. The dominant trophic levels in the impoundment fish community were the herbivore/detritovores, whereas the seagrass bed fish community was dominated by secondary consumers. 3. The impoundments were dominated by five atheriniform fishes ( Cyprinodon variegatus , Poecilia latipinna , Gambusia affirm , Lucania parva , and Menidia peninsulae ), and the clown goby, Microgobius gulosus . 4. In the seagrass beds the dominant community residents were '-"'^^"^'3 Rarya , Menidia peninsulae , Microgobius gulosus , Gobiosoma robustum, and Syngnathus scovelli . Important seasonal recruits to the seagrass beds, primarily represented as juveniles, were Lagodon rhomboides and Bairdiella chrysoura . 5. Mean densities of fish in the impounded marsh were 16.5-27.5 (Ind/m ) while densities in the seagrass beds were only 3.6-7.3 (Ind/m^). 5. Mean standing crops of fish were 53.7-58.5 kJ/m^ in the impoundments and 5.6-6.9 kJ/m^ in the seagrass beds. The number of species, density, and standing crop were used as indicators of structural complexity of the community. At least

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98 one of the three indicators had a significant (p < 0.05) positive correlation with the median monthly water temperatures at each site. Only standing crop of fish at site 12 was found to be significantly correlated with salinity. This last correlation is not interpreted as a direct response of the fishes to varying salinities, but actually the result of changing relative densities of fishes as water levels vary in the impoundment, i.e. with increased evaporation, water level drops, salinity goes up, and total marsh surface area decreases. In the seagrass beds the two fish communities had very different responses to seagrass density. At site SI, community complexity showed almost no correlation to seagrass density, while at site S2, increasing complexity was significantly correlated with greater seagrass density. The annual fish production estimates for sites II, 12, SI, and 32 were 281.46, 191.75, 12.95, and 13.05 kJ-m'^-y'^ respectively. Relative to other fish communities, the impoundments are extremely productive and the seagrass beds are only moderate. Over 87% of the fish production at II was by herbivorous/ detritivorous fishes, whereas fish production of the other sites was primarily by secondary consumers. The conversion of solar energy into fish production at II involved one less transfer than is common for many temperate fish communities. The ratios of annual production to average standing crop appear to indicate that the fishes in either habitat are not energy limited and that the fish community of the impoundment has a turnover rate of approximately twice that of the seagrass bed community.

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99 12. Annual respiratory losses at II, 12, SI, and S2 were 512, 655, -2 -1 60, and 81 kJ-m -y , respectively. Community respiration was greatest during the summer as a result of higher densities and higher water temperatures. 13. Annual consumption by the impounded marsh fishes was estimated to be an order of magnitude greater per unit area than the fishes of the seagrass beds. Consumption in the impoundments, 11-12, -2 -1 was 992-1059 kJ'm -y and in the seagrass beds, S1-S2, was. 91-118 kJ.m'^.y"^ 14. In comparing the ratios of production to consumption, the impoundment community appears to be more efficient at converting consumed energy into net fish production than the seagrass bed community. Stated another way, the seagrass bed communities use greater percentages of consumed energy for respiratory and maintenance purposes than do the impoundment communities. 15. The overall efficiency of conversion of incident solar radiation into fish production was 0.0042% for II, 0.0029% for 12, 0.00019% for SI, and 0.00020% for S2. The efficiency of II should be viewed with caution since most of the fish production was by herbi vores/detritivores as opposed to secondary and tertiary consumers. Production in temperate fish communities is generally by fishes feeding as secondary and tertiary consumers. 16. The efficiency of seagrass bed systems at converting solar energy into fish production is relatively low for shallow water systems due to the low efficiency of transfer of incident solar energy into net seagrass production. The former is

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100 more comparable to efficiencies of continental -shelf and large lake communities. Impoundment II had a very high efficiency of transfer of solar energy into fish production, partially as a consequence of the high percentage of herbivorous/detritivorous fishes. Site 12 was more characteristic of temperate fish communities, with most of its production by secondary consumers. Site 12 was only 70% as efficient as II, but is still highly efficient for temperate fish communities in general.

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REFERENCES 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. Allen, K.R. 1950. The computation of production in fish populations. N.Z. Sci. Rev. 8:89. Backiel, T. 1971. Production and food consumption of predatory fish in Vistula River. J. Fish Biol. 3:369-405. Bardach, J.E. 1959. The summer standing crop of fish on a shallow Bermuda reef. Limnol. Oceanogr. 4:77-85. Benedict, F.F. 1976. Herbivory rates and leaf properties in four forests in Puerto Rico and Florida. M.S. Thesis. University of Florida, Gainesville. Burgis, M.J. and I.G. Dunn. 1978. Production in three contrasting ecosystems. I^: S.D. Gerking (ed.). Ecology of freshwater fish production. Halstead Press, New York. Cameron, J.N. 1969. Growth, respiratory metabolism, and seasonal distribution of juvenile pinfish ( Lagodon rhomboides Linneaus) in Redfish Bay, Texas. Pubis. Inst. Mar. Sci. Univ. Tex. 14:19-36. 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. Amer. Fish Soc. 1 02(3) :51 1 -540. Chapman, D.W. 1978. Production in fish populations. In: S.D. Gerking (ed.). Ecology of freshwater fish production. Halstead Press, New York. Clark, K.B. 1975. Benthic community structure and function. InAn ecological study of the lagoons surrounding the John F.Tennedy Space Center, Brevard County, Florida, April, 1972 to September, 1975. Final report to KSC/NASA, December 31, 1975 by the Florida institute of Technology, Melbourne, NGR 10-015-008. 101

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102 Clarke, G.L. 1946. Dynamics of production in a marine area. Ecol Monogr. 16:322-335. Cummins, K.W. and J.C. Wuycheck. 1971. Caloric equivalents for investigations in ecological energetics. Int. Ver. Theor Angew. Limnol . Verh. , Bd 18, S. 1-158. Davis, G.E. and C.E. Warren. 1965. Trophic relations of a sculpin in laboratory stream communities. J. Wildl. Mgmt. 29:846-871. Day, J.W., Jr., W.G. Smith, P.R, Wagner, and W.C. Stowe. 1973. Community structure and carbon budget of a salt marsh and shallow bay estuarine system in Louisiana. Center for Wetland Resources, Louisiana State University, Baton Rouge, Publ . No. LSU-56-72-04. Dubbelday, P.S. 1975. Lagoonal circulation, hi: An ecological study of the lagoons surrounding the John F. Kennedy Space Center, Brevard County, Florida, April, 1972 to September, 1975. Final report to KSC/NASA, December 31, 1975 by the Florida Institute of Technology, Melbourne, NGR 10-015-008. Edwards, R.R.C. 1968. Estimation of the respiratory rate of young plaice ( Pleuronectes Plat^ssa L. ) under natural conditions, usinq zinc-65. Nature, Lond. 216-1335-1337. Eiseman, N.J., M.C. Benz, and D.E. Serbousek. 1976. Studies on the benthic plants of the Indian River region. Ln: D.K. Young (ed.), Indian River coastal zone study, third annual report, 1975-1976 Vol. I. Harbor Branch Consortium, Ft. Pierce, Florida. Ferguson, R.L. and S.M. Adams. 1979. A mathematical model of trophic dynamics in estuarine seagrass communities. In: R.F. Dame (ed ) Marsh-estuanne systems simulations. University of South Carolina Press, Columbia, pp 41-70. Gilmore, R.G. 1977. Fishes of the Indian River Lagoon and adjacent waters, Florida. Bull. Florida State Mus., Biol. Sci. 22(3): 1 01 1 48 . Gilmore, R.G. , G.R. Kulezycki, P. A. Hustings, and W.C. Magley. 1976 Studies of fishes of the Indian River Lagoon and vicinity. In: U.K. Young (ed.), Indian River coastal zone study, third annual nS?ida "3^^°^ B^^"ch Consortium, Ft. Pierce, ''°^^^cq/co; ^"^"^^y values of ecological materials. Ecol. 42: bo I -bo4 . Harrington, R.W. Jr. , and E.S. Harrington. 1961. Food selection among fishes invading a high subtropical salt marsh: From onset of 646 666^ progress of a mosquito brood. Ecol. 42(4)-

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103 Harvey, H.W. 1950. On the production of living matter in the sea off Plymouth. J. Mar. Biol. Ass. U.K. 29:97-137. Hayne, D.W. and R.C. Ball. 1956. Benthic productivity as influenced by fish predation. Limnol . Oceanogr. 1:162-175. Heald, E.J. 1969. The production of organic detritus in a south Florida estuary. Ph.D. Dissertation, University of Miami, Florida. Hellier, T.R. 1962. Fish production and biomass studies in relation to photosynthesis in the Laguna Madre of Texas. Pubis. Inst. Mar. Sci. Univ. Tex. 8:212-215. Ivlev, V.S. 1966. The biological productivity of waters. J. Fish. Res. Bd. Can. 23:1727-1759. Jones, R.S., R.G. Gilmore, Jr., G.R. Kulezycki, and W.C. Magley. 1974. Studies on the fishes of the Indian River region, jji: Indian River study, 1973-1974 annual report. Vol. I. Harbor Branch Consortium, Ft. Pierce, Florida. Jones, R.S., R.G. Gilmore, Jr., G.R. Kulezycki, W.C. Magley, and B. Graunke. 1975. Studies of the fishes of the Indian River coastal zone. In_: O.K. Young (ed.), Indian River coastal zone study, 1974-1975 annual report. Vol. I. Harbor Branch Consortium, Ft. Pierce, Florida. Kerr, S.R. 1971a. Analysis of laboratory experiments on growth efficiency of fishes. J. Fish Res. Bd. Can. 28:801-809. Kerr, S.R. 1971b. Prediction of growth efficiency in nature. J. Fish. Res. Bd. Can. 28:809-814. Kerr, S.R. 1971c. A simulation model of lake trout growth. J. Fish. Res. Bd. Can. 28:815-819 Krogh, A. 1916. Respiratory exchange of animals and man. Longmans Green and Co., London. Lasater, J. A. 1975. Water chemistry studies of the Indian River lagoons. Jm: An ecological study of the lagoons surrounding the John F. Kennedy Space Center, Brevard County, Florida, April, 1972 to September, 1975. Final report to KSC/NASA, December 31, 1975 by the Florida Institute of Technology, Melbourne, NGR 10-015-008. Lugo, A.E. and S.C. Snedaker. 1974. Properties of a mangrove forest in southern Florida, ^n: G.E. Walsh, S.C. Snedaker, and H.J. Teas (eds.). Proceedings of the international symposium on biology and management of mangroves. Vol. II. IFAS, University of Florida, Gainesville.

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104 MacKinnon, J.C. 1973. Analysis of energy flow and production in an ^n?J?\*7oo'"^^^""^ flatfish population. J. Fish. Res. Bd. Can. oU r I / 1 /1 728 . Mann, K.H. 1965. Energy transformations by a population of fish in the River Thames. J. Animal. Ecol . 34(2) :253-275. Mann, K.H. 1978. Estimating the food consumption of fish in nature. TT-l S.p. Gerking (ed.), Ecology of freshwater fish production. Halstead Press, New York. Mathews, C. P. 1971. Contribution of young fish to total production of fish in the River Thames near Reading. J. Fish. Biol. 3:157180. McRoy, CP. and C. McMillan. 1977. Production ecology and physiology of seagrass. In: CP. McRoy and C. Helfterich (eds.), Seagrass ecosystems: A scientific perspective. Marcel Dekker Inc., New York, 314 pages. Merriman, D. and H.E. Warfel. 1948. Studies on the Marine resources of southern New England. VII. Analysis of a fish population. Bull. Bingham Oceanogr. Coll. 11:131-163. Naiman, R.J. 1976. Productivity of a herbivorous pupfish ( Cyprinodon nevadensis ) in a warm desert stream. J. Fish Biol. 9:125-137. ^"^^"^'nb^.'. ]^^^.Fundamentals of ecology, 3rd edition. Saunders, Philadelphia. Odum, H.T. 1967. Biological circuits and marine systems of Texas In: T.A. Olson and F.J. Burgess (eds.). Pollution and marine ecology. John Wiley, New York. Odum, H T., W.M. Kemp, W.H.B. Smith, H.N. McKeller, D.L. Younq, M E Lehman, M.L. Homer, L.H. Gunderson, and A.D. Merriman 1974* Power plants and estuaries at Crystal River, Florida: An energy evaluation of the system of power plants, estuarine ecology and alternatives for management. Report from the Systems Ecology Group, Dept. of Envir. Eng. Sci., University of Florida, Gainesville to the Florida Power Corporation, St. Petersburg, Florida, Contract #GEC-159 918-200-188-19, October, 1974. °'^"'"'<;p;^r. ^Tl' J^l^l^^^ °^ ^"^"^9^ 3 south Florida estuary. Sea Grant Tech. Bull. No. 7, com-71-01066. Odum, W.E. and E.H. Heald. 1972. Trophic analyses of an estuarine mangrove community. Bull. Mar. Sci., 22(3) :671 -738. Paine, R.T. 1971 The measurement and application of the calorie to ecological problems. Ann. Rev. Ecol. Syst. 2:145-164.

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105 Parr Instrument Company. 1969. Instructions for 1241 and 1242 adiabatic calorimeters. Manual No. 142, 1-23. ftoline. 111. Phillips, R.C. 1960. Observations on the ecology and distribution of Florida seagrasses. Prof. Pap. Ser. Fla. State Bd. of Conserv. 2:1-72. Phillips, R.C. 1974. Temperate grass flats. In: H.T. Odum, B.J. Copeland and E.A. McMahan (eds.). Coastal ecological systems of the United States, Vol. 2. The Conservation Foundation, Washington, D.C., pp. 244-299. Pool, D.J., A.E. Lugo, and S.C. Snedaker. 1974. Letter production in mangrove forest in southern Florida and Puerto Rico. In: G.E. Walsh, S.C. Snedaker and H.J. Teas (eds.), ProceedingsTf the international symposium on biology and management of mangroves. Vol. II. IFAS, University of Florida, Gainesville. Provost, M.W. 1969. Ecological control of salt marsh mosquitos with side benefits for birds. Proc. Tall Timbers conference on ecological animal control by habitat management. No. 1. Provost, M.W. 1973. Salt marsh management in Florida. Proc. Tall Timbers conference on ecological animal control by habitat management. No. 5. Rich, P. H., R G. Wetzel, and N.V. Thug. 1971. Distribution, production, and role of aquatic macrophytes in a southern Michigan marl lake. Freshwat. Biol. 1:3-21. Ricker, W.E. 1946. Production and utilization of fish populations Ecol. Monogr. 16:374-391. Ricklefs, R.E. 1979. Ecology, 2nd ed. Chiron Press, Concord, Mass. Schooley, J.K. 1977. Factors affecting the distribution of the nearshore fishes in the lagoonal waters of the Indian River, Honda. M.S. Thesis, University of Florida, Gainesville. Slobodkin, L.B. 1960. Ecological energy relationships at the population level. Am. Naturalist. 94(876) :213-236. Snelson Franklin F Jr. 1976. A study of a diverse coastal ecoI Atlantic coast of Florida, Vol. 1., Ecthyological 1976:"(NGr"^1o19^^S?° ''''' ''''''' ^^^^ ^'^--^ Subrahmanyan C.B. and S.H. Drake. 1975. Studies on the animal conimunities in two north Florida salt marshes. Part I Fish Communities. Bull. Mar. Sci. 25(4) :445-465.

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106 Thayer, G.W., S.M. Adams, and M.W. LaCroix. 1975a. Structural and functional aspects of recently established Zosteria marina community, in: L.E. Cronin (ed.), Estuarine resear^hT^Vol . 1 Academic Press, New York. Thayer, G.W., W.E. Schaaf, J.W. Angeloric, and M.W. LaCroix. 1973 Caloric measurements of some estuarine organisms. Fish Bull U.S. 71:289-296. dum., Thayer, G.W., D.G. Wolfe, and R.B. Williams. 1975b. The impact of man on seagrass systems. Amer. Sci. 63:288-296. Thomas, J.R. 1974. Benthic species diversity and environmental stability in the northern Indian River, Florida. M.S. Thesis Florida Inst, of Tech., Melbourne. Ware, D W. 1975. Growth, metabolism, and optimal swimming speed of pelagic fish. J. Fish. Res. Bd. Can. 32:33-41. Webb, P. W. 1978. Partioning of energy into metabolism and growth. In: S.D. Gerking (ed.). Ecology of freshwater fish production. Hal stead Press, New York. Welch, H.E. 1968. Relationships between the assimilation and growth efficiencies for aquatic consumers. Ecol . 49(4) :755-759. Welcomme, R L. 1975. The fisheries ecology of African floodplains. FAQ CIFA Technical Paper No. 3. FAG, Rome. Whitfield, A.K. 1980. A quantitative study of the tropic relationships within the fish community of the Mhlanga estuary. South Africa. Est. Cost. Mar. Sci. 10:417-435. Whittaker, R.H. 1975. Communities and ecosystems, 2nd ed Macmillan, New York. Winberg, G.G. 1956. Rate of metabolism and food requirements of fishes. Tr. Beloruss. Godudanst. Univ. Im. Vol. 1. Lenina, No"'l94 I960) ^''^ ^"^^ ^^^^

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BIOGRAPHICAL SKETCH James K. Schooley was born on November 8, 1951, in Tulsa, Oklahoma. He began his undergraduate studies at the United States Coast Guard Academy in New London, Connecticut. His undergraduate studies were completed at Florida Institute of Technology in Melbourne, Florida, where he graduated summa cum laude in 1975, with a B.S. in oceanography. He received his M.S. in 1977 from the Department of Zoology at the University of Florida. After receiving his Ph.D he will join the faculty at California State University at Hayward. In the summer of 1973, he was married to the former Kathryn Anne Heckenkemper, also of Tulsa, who is a CPA with Peat, Warwick, ' Mitchell and Co. 107

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I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. Professor of Zoology I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy, Associate Professoijlof Zoology I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. Stephen Bl oom Assistar/t Professor of Zoology I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate in scope and quality, as a dissertation for the degree of Doctor of Philosophy. ^/iOerbme V. Shi reman Trofessor, Forest Resources and Conservation

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This dissertation was submitted to the Graduate Faculty of the Department of Zoology in the College of Liberal Arts and Sciences and to the Graduate Council, and was accepted as partial fulfillment of the requirements for the degree of Doctor of Philosophy. December 1980 Dean, Graduate School


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