ecotopic and ontogenetic trophic variation in mojarras...

Estuaries Vol. 6, No. 3, p. 3114322 September 1965

Ecotopic and Ontogenetic Trophic

Variation in Mojarras

(Pisces: Gerreidae)’

BARBARA A. KERSCHNER

Florida Institute of Technology Department of Oceanography and Ocean Engineering Melbourne, Florida 32901

MARK S. PETERSON

University of Southern Mississippi Department of Biological Sciences Hattiesburg, Mississippi 39406-5018

R. GRANT GILMORE, JR.

Harbor Branch Foundation, Inc. R.R.1 Box 196 Ft. Pierce, Florida 33450

ABSTRACT: Seven species of mojarras (Gerreidae) were collected from three stations in the Indian giver lagoon near the Sebastian Inlet, Florida over an eighteen month period to study spatial and temporal variations in occurrence and feeding habits. Two major habitats common to this area were represented in the study; a sandy beach and a seagrass flat. Of the 2,899 gerreids collected, Eucinostomus gula represented 67% and was found primarily in the Halodule seagrass site. The next most abundant species, E. argenteus (ll%), E. jonesi and E. lefroyi (each lo%), were found most frequently at the inlet site. Diapterus auratus, E. melanopterus, and Gerres cinereus were captured infrequently and were considered incidental. Prey items found included amphipods, bivalves, copepods, fish eggs, foraminifera, isopods, nematodes, ostracods, polychaetes and crustacean parts. Significant amounts of sand and unidentifiable amorphous debris were also included in the gut content analysis. Little interspecific variation in diet was found among the four major species examined. The general shift seen from a diet composed primarily of copepods and other crustaceans to one of polychaetes suggests an intraspecific ontogenetic progression. Spatial variations in diet composition were also indicated between the two major habitats. Feeding analyses showed gerreids to be diurnal feeders with the greatest consumption (total gut content weight) occurring at dusk.

Introduction Mojarras, family Gerreidae, are among

the common fish species inhabiting the nearshore waters of Florida (Reid 1954; Springer and Woodburn 1960; Carr and Adams 1973; Gilmore 1977). While mainly found in estuarine habitats, gerreids have been reported from freshwater tributaries,

sand beaches, shallow reef formations and open neritic waters (Randall 1967; Gilmore 1977). Mojarras are mainly benthic feeders with highly protrusible mouths and have been observed foraging for infaunal inver- tebrates (Randall 1967). Studies have shown them to feed primarily on copepods, amphipods, mysids, shrimps, pelecypods, ostracods, nematodes, polychaetes, and detri- tus (Reid 1954; Odum 1970; Carr and Adams 1973).

’ Contribution No. 470 of the Harbor Branch Foun- Few comprehensive studies have been dation, Inc. and contribution No. 63 of the Florida conducted exclusively on gerreids although Institute of Technology. they are abundant and occupy an important

0 1985 Estuarine Research Federation 311 0160-6347/65/03031 I-1 2$01.50/O

312 !3. A. Kerschner et al.

Fig. 1. Study location in the Indian River lagoon.

trophic link in estuarine food webs (Odum 1970). Data available on mojarras in the southeastern United States and Caribbean include only those extracted from major fauna1 works. The most detailed studies to date concern: Gerres oyena and 6. jilamentosus (Rao 1968); D. rhombeus (Austin 197 1); G. acinaces, G. oblongus, G. oyena, G. Jilamentosus and G. rappi (Cyrus and Blaber 1983a, 1983b, 1984).

The limited knowledge of gerreid feeding ecology in Florida led to the development of this study. Our goal was to examine feeding habits of the gerreid family in the Indian River lagoon, a polyhaline Florida estuary. Specific objectives included examination of diel, ontogenetic, and spatial variation in diet and habitat utilization.

Methods STUDY AREA

The Indian River is a natural estuarine lagoon located along the Atlantic coast of central Florida. Three stations were selected at two sites near the Sebastian Inlet (Fig. 1). These sites were representative of two major

habitats common in this area; sandy bottom areas and seagrass flats.

The first station bordered a beach on the northern side of the inlet proper. The bottom contour slopes gradually downward un- til reaching the main channel (4-5 m deep) about 10 m from shore. Strong inlet tidal currents influence the mixture of sand, car- bonate beach rock and shell hash which characterize the substratum. Aquatic vegetation is limited to drift algae.

The second site was located approxi- mately 1.5 km south of Sebastian Inlet in a lagoon seagrass flat, within the range of tidal influence. The area has a 66% plant cover comprised primarily of manatee grass, Sy- ringodium @j&me and shoal grass, Halo- dule wrightii {Thompson 1976). An offshore sandbar bisects this flat about 110 m from shore and separates the two lagoon stations. The inshore station, reaching depths of 1.5 m, is composed primarily of Halodule grass; the offshore station, sloping downward to- ward the main channel, is comprised mainly of Syringodium grass. Both seagrass stations also support a diverse flora of macroalgae. Red mangrove, Rhizophora mangle, and black mangrove, Avicennia germinans, dominate the shoreline vegetation.

COLLECTION PROCEDURES Biweekly morning and evening collec-

tions of fish were taken from all three stations between 30 October 1980 and 30 Oc- tober 198 1; monthly samples were collected from 12 November 198 1 through 9 April 1982. Species capture rate per month is listed in Table 1. Collections were made with a 3.05 x 1.22 m seine constructed of 4.7 mm “ace” netting. Seven consecutive net hauls (6-7 m in distance) were taken at each station. The inlet topography caused a spatial overlap of several pulls during each sampling period, no spatial overlap occurred in the seagrass site within a given sampling.

Upon capture, all gerreids were imme- diately placed in a narcotizing agent (5Oh ethanol solution) and then preserved in 20% buffered formalin. Fishes larger than 50 mm in standard length (SL) were also injected intraperitoneally. Specimens were fixed for one week, rinsed in water and transferred to 70% ethanol for storage.

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Ecotopic and Ontogenetic Trophic Variation 313

On 15-l 6 May 1982, specimens were collected and preserved every four hours through a 24 hour period in the Halodule station to examine short term die1 feeding patterns. Following identification and separation by size class the most complete group collected, 20-29 mm E. gula, was analyzed for comparison with morning and evening samples.

FEEDING ECOLOGY

Identified specimens were sorted by species into 10 mm SL size class sample groups based on station, sample period and date. Entire digestive tracts were analyzed for a random sample of up to 20 individuals from each group. Sorted prey items were identified to the lowest possible taxon, dried at 75 “C to constant weight, and weighed to +0.0001 g.

Diet components were evaluated in terms of: % frequency of occurrence (FO), exam- ining sample group specimens individually; % dry weight (DW), pooling all individuals from each sample group; and die1 feeding changes for each species. Limitations of these methods have been reviewed by Berg (1979) and Hyslop (1980).

The relative % DW and FO compositions of all prey categories are listed in Tables 2 and 3. Fecal pellets and sand grains intact in the alimentary tract of a prey organism were classified with that organism; those found within the open digestive tract of the fish were classified separately. For the pur- pose of histogram presentation, polychaetes and polychaete parts were considered polychaete tissues; amphipods, isopods, and un- identified crustacean parts were considered crustaceans. No distinction was made between veligers and juveniles for bivalve types.

Results Collections produced 2,899 gerreids dm-

ing the study period (Table 1). Of this total catch, Eucinostomus gula accounted for 67%, E. argenteus 1 l%, E. jonesi and E. lefrovi 10% each. The remaining species, Diapterus auratus, Gerres cinereus and E. melanopterus together comprised 2% of the total catch and were considered incidental. Because of their low abundance, these three species were not included in the feeding analysis.

314 6. A. Kerschner et al.

TABLE 2. Dry weight of prey items for morning and evening sampling periods. DW is reported as a percentage of the total DW of all prey items consumed at a given site by each species. IN = Inlet; IB = Hulodtde; OB = Syringodium.

E. ai-genteus E. ,&a E. jonesi E. iefroyi Food Categories IN IB OB IN IB OB IN IB OB IN

Amorphous debris Bivalves Calanoid copepods Caprellid amphipods Gammarid amphipods Fecal pellets Harpacticoid copepods Isopods Miscellaneous Nematodes Ostracods Polychaete parts Polychaetes Sand grains Und. crust. parts

Amorphous debris Bivalves Calanoid copepods Gammarid amphipods Fecal pellets Fish eggs Harpacticoid copepods Miscellaneous Nematodes Oligochaetes Ostracods Polychaete parts Polychaetes Sand grains Und. crust. parts

17 20

3 4

3 4

1 :1 10 l!)

!)

9 21

13 8

1’3

11: 18

11 16 10

Morning DW data 21 31 12

19 21 5

3

7

9

20 7

1 2 5 4 4 5

13

10 10 5

5 7 2 5

20

8 4

3 5 3 11 28

17

13

8

12 18 16 7 25 10 6

Evening DW data 17 19 17

22 3 3

10

8 21

6 10

11

5

12 26 3 3 7 5 6 2

7 16 2 2 4 11 20 23 23

2 6 21 24 9 13 6 11

12 36 14 6 6

8 10

4

13 17

21 21

13

3 8

3 27

I 40

40

60

19

34

21

12 13

32 8 16

41 3

16

3 3

11

6 5

19 27 10

13 9 6

20 3 27

5 2

15 7 1 9

3 9 5

14 2

14 9 14 9

Consumed prey items included amphipods, bivalves, copepods, fish eggs, fecal pellets, foraminifera, isolpods, nematodes, oligochaetes, ostracods, polychaetes, un- identified crustacean parts, and amorphous debris (Table 2). Sand grains were found in many individuals regardless of size or capture location. In general, a lower % DW of copepods and other crustalceans and a higher % DW of polychaete tissues appeared with increasing fish size.

Eucinostomus argenteus GENERAL L)IET

Eucinostomus argenteus occurred in collections each month from October 1980 through February 198 1 exlcept February and March 1980 and January 1981. The 318

individuals captured ranged in size from 10 to 104 mm SL. Prey composition varied little between morning and evening samples within a given station.

Bivalves, crustaceans and polychaetes were the major prey items in the morning inlet specimens. Bivalve and crustacean consumption remained fairly constant at 20- 25% DW for each size class. Polychaete tissues ranged from -8% to -30% DW. In the evening inlet sample, bivalves contributed -30% DW of the 30-69 mm individuals’ diets, complimented by -20% DW crustaceans. For the 60-99 mm group, polychaete tissues averaged -28% DW while bivalve consumption was reduced to - 12% DW (Fig. 2).

In the morning collection at the Halodule


TABLE 3. Frequency of occurrence of prey items for morning and evening collection periods. Frequencies are reported as a percentage of the number of individuals in which the prey items occurred at a given site by each species. IN = Inlet; IB = Halodulq OB = Syringodium.

E. argentnrs E. gada E. jonesr E. lefroyi

IN IB OB IN IB OB IN IB OB IN

Morning FO data Algae Amorphous debris Bivalves Calanoid copepods Caprellid amphipods Crepidula sp. Gammarid amphipods Fecal pellets Fish eggs Harpacticoid copepods Isopods Miscellaneous Nematodes Ostracods Polychaete parts Polychaetes Sand grains Und. crust. parts

Amorphous debris Bivalves Calanoid copepods Caprellid amphipods Cladocera Gammarid amphipods Fecal pellets Fish eggs Harpacticoid copepods Hydroid polyps Invertebrate eggs Miscellaneous Nematodes Ostracods Polychaete parts Polychaetes Sand grains Und. crust. parts

70 63

6 20

20

41

20 64 28

30 7

51 52

34 33

36 7 6

8 40

5 11 19

23 30

3 6 6

26 33 53 63

31 7

60 45 15

10 10 10 10 10 10 75

20 7 10 14

28

20 35 80 42

16 9 36 25 25 23 69 42 29 26 35 79 54 61

43 64

36

21

Evening FO data 56 37 28

43 7 17

30

12 24 9

12 6 13 33

14 6

40 14 6 28

: 6

21

10 8 12 8 8 19 2.5 7 28 24 26 19 14 19 16 26 42 19 24 47 43 22 10 9 29 26 47 24 28 21 22 70 33 28 32 29 39

25 25

16

16

5 31 22 31 12

16

8 8 45

8 50 16

66 66 100

20

17

66

:: 15 12 10 7

19 12 36 89

44 6

21

7 13 12

13 33 45 36

7 12 7

10 7 34

10

7

17 28 70 18 72

6 21 11 10 33

8 35 57

grassbed, bivalves, copepods, other crus- Few specimens were encountered in the taceans and polychaetes were the major prey Syringodium bed. Major prey items for the items. The 10 mm size class consumed only morning collections included copepods and copepods and various other crustaceans other crustaceans. Crustaceans (- 6 5% DW) which formed -90% of the total DW com- and ostracods (-35% DW) comprised the position. Bivalves, found only in the 30 mm diet of the lo-19 mm size class. The 20-29 group, comprised -27% DW. Polychaetes mm size class exhibited a greater variety in were present in both the 20 and 30 mm size diet, including bivalves, calanoid and har- classes. For the evening sample, bivalves, pacticoid copepods and various other crus- copepods, and other crustaceans composed taceans. The 30-39 mm size class was rep- -70% of the DW composition in the 1 O- resented by an individual which ingested 19 mm fish. Polychaetes replaced bivalves primarily copepods and other crustaceans. in the 20-39 mm spec:imens, and formed Only two size classes, 1 O-29 mm, were found 40-85% DW in the 50-69 mm fish (Fig. 2). at this station during the evening collec-

316 8. A. Kerschner et al.

Inlet a.m.

Halodule a.m.

F t ”

Inlet p.m.

Holodufe pm

loo-

go-

eo- 70-

so- 50-

40-

30-

20-

IO-

0-

Syhgodium am. Syrihgcw+ikn p.m.

I O”4, 5/ I/

I J

n 65’ 5m Bivalves copepcds crustoceans Fdychoetes Sand Other

Fig. 2. Diet of E. argenteus from each of the stations. Histograms represent stomach contents based on the % DW of major food categories. Numbers above histograms represent size classes of fish in mm SL. Numbers below histograms represent the number of fish with food in the digestive tracts over the total number of fish examined.

Inlet 0.m

Hu~ooWe 0.m

Ecotopic and Ontogenetic Trophic Variation

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IOO-

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00-

?O-

60-

50-

40-

30-

20-

to-

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I I 4J4 61. 76 Wg

Hahfule p. m.

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D ao- s - ?O- r z 6Q- p 0’ 50-

o 40-

E Q 30-

p 20- In

IO-

Syrinqodiim 0.m. Syringodium p.m.

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,9 20-B 3c39 4oig 5oig 60eg

go-

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70-

60-

50-

40-

3D-~

20-

IQ-

O L , , 3w3647s4 4065 305, 4% I/,

q N@Hlgr-J

Blualves copepods Crustaceans Polychaetes Sand Other

Fig. 3. Diet of E. g&a from each of the stations. Histogram presentation f&lows that in Fig. 2.

318 B. A. Kerschner et al.

70 1 Eucinostomm gula 20-29mm SL

3/5

015

r-7

TIME OF DA”

Fig. 4. Die1 feeding habits of E. gula based on the total DW of stomach contents. Numbers above the histograms represent the number of fish containing food in the digestive tract over the total number of fish examined.

tions. Food of these fish included copepods, crustaceans and ostracods (Fig. 2).

Eucinostomus gula GENERAL DIET

Eucinostomus gula was collected in morning and evening samples each month except March 198 1. The 1,942 individuals captured ranged in size from 10 to 109 mm SL. Prey composition varied little between morning and evening samples within a given station.

Morning collections from the inlet produced few individuals, these typically from the 50-109 mm size classes. Major dietary components included bivalves, crustaceans, ostracods, and amorphous debris. Analysis of the evening collections showed the major components to include bivalves, crustaceans and polychaetes. Nothing was found in the gut of the 1 O-l 9 mm individual. Prey of the 30-49 mm fish included -30% DW bivalves and -40% DW crustaceans. In the 50-89 mm size group, a decrease to - 12% DW of crustaceans was observed, with polychaete tissues averaging -30% of the DW content. For the 90-109 mm fish, bivalves (-8% DW), polychaetes (-25% DW) and amorphous debris (-63% DW) were the primary dietary components (Fig. 3).

Copepods, other crustaceans and polychaete tissues were the major items consumed by fish from the Halodule seagrass

flat in the morning collections. Crustaceans remained fairly constant at - 10% DW in each of the size classes, although they were absent in the 60-69 mm fish. Bivalves appeared only in the 50-59 mm group. Eve- ning collection fish in the lo-59 mm size classes fed primarily on copepods (- 3-25% DW), various other crustaceans (- 3-30% DW), and polychaete tissues (- 8-60% DW). The 60 mm individual had a more diverse diet which included fecal pellets, invertebrate eggs and ostracods (Fig. 3).

Morning collections from the Syringo- dium grass showed copepods, other crustaceans, and polychaetes to be the major diet constituents. Copepods and crustaceans formed -90% DW of the diet of the 1 O-l 9 mm fish. Polychaete tissues frequently dominated the prey composition in the 20-59 mm fish, averaging -37% DW. Co- pepods and various other crustaceans accounted for - 80% DW in the 10-l 9 mm fish in the evening collections. In the 30-80 mm size classes, crustaceans decreased to - 10% DW, while polychaete tissues ranged from -28-70% DW (Fig. 3).

DIEL COMPARISON

The 24 hour feeding study was analyzed by total DW using the 20-29 mm size class. Prey items appeared in the digestive tract in the early morning collection and were present throughout the day ranging from 20- 40 x 10e4 g. A peak in the amount of consumed materials (55 x 10e4 g) occurred at dusk. In late evening, the total weight of prey items found in the gut decreased to 15 x 10d4 g, while the first appearance of empty guts was recorded. No prey items occurred in the guts after midnight (Fig. 4).

Eucinostomus jonesi GENERAL DIET

Eucinostomus jonesi was collected at each of the study sites during both morning and evening sampling periods from July 198 1 through January 1982. The 288 specimens captured ranged in size from 10 to 109 mm SL. Similar prey items were found in the morning and evening samples for each station.

A high degree of variability in diet was seen among the individuals comprising the


Inlet 0.m.

El jonesi Inlet cm

Hofodule a.m. kfafodufe D m

Syringodiim a.m. Syringodium p.m.

100

90

2 80 2 0

70

r 60

5 ‘; 50

s 40

6 9 30

p 20

* IO

0

Bivalves Copepods Crustaceans Polyctxletes Sand Other

Fig. 5. Diet of E. jonesi from each of the stations. Histogram presentation follows that in Fig. 2.

320 B. A. Kerschner et at.

Inlet a.m.

.E. leff oyi

Inlet pm. Hafodule a.m.

Bivalves Capepods Crustaceans Polychaetes Sand Other

Fig. 6. Diet of E. Zefoyi kom the inlet and Halodule stations. Histogram presentation fallows that ia Fig. 2.

small sample of the inlet mofrning collections. The primary constituents included bivalves, crustaceans, and polyclhaetes. In the evening, - 80% DW of the major prey items included bivalves, crustaceans and polychaetes. Copepods and various other crustaceans formed - 80% DW of the diet of the lo-19 mm fish. In the 20-59 mm fish, bivalves, crustaceans and polychaetes formed -70-l 00% DW of the prey, remaining rel- atively constant in each of the size classes. Polychaete tissues composed 98% DW of the diet of the 70-79 mm group. Guts of the 100 mm individuals were empty (Fig. 5).

For the Hulodule station during both the morning and evening, copepods and other crustaceans were consumed by the fish examined. Ostracods and sand also appeared in the 10 mm class from the evening group (Fig. 5).

The morning sample from the Syringo- dium station showed crustaceans to be a food source of both size classles. Copepods and amorphous debris were also found in the larger fish. In the evening, the diet of

the lo-29 mm fish consisted mainly of copepods (-40% DW), other crustaceans (-25% DW), and ostracods (- 5% DW). Bi- valves, copepods, fecal pellets and oligo- chaete worms were consumed by the 30-39 mm individual (Fig. 5).

Eucinostomus lefroyi GENERAL DIET

Eucinostomus lefroyi appeared in collections during November 1980, January 198 1, and May through December 198 1. The 290 specimens collected ranged from 10 to 69 mm SL. Prey items were similar in the morning and evening samples.

Major prey items in the morning samples included bivalves, copepods, other crustaceans and polychaetes. The lo-29 mm fish ate -70% DW copepods and crustaceans. Bivalves (1 O-30% DW) and polychaete tissues (8-40% DW) were present in the 30- 50 mm classes. Major items found in the evening samples included primarily copepods, various other crustaceans and polychaete tissues. Crustaceans formed -22- 78% DW in the lo-29 mm fish, decreasing


to - 7-22% DW in the 30-59 mm fish. Poly- chaete tissues ranged from -6% DW in the lo-29 mm classes, to - 1537% DW in the 30-59 mm group and 100% DW in the 60- 69 mm individual (Fig. 6).

INTERSPECIFIC COMPARISON General Diet

Little difference in diet was observed among E. argenteus, E. gula, 6. jonesi and E. lefroyi. Bivalves, copepods, other crustaceans, ostracods, polychaete tissues, sand and amorphous debris comprised the major categories of ingested materials, while other food items occurred less frequently (Table 3).

Discussion A highly diverse gerreid species compo-

sition was found in the Sebastian Inlet re- gion. Five of the seven gerreid species observed were collected at the inlet site, while each was represented in collections at the seagrass site. A varied species assemblage commonly occurred within the same seine haul. Several reports have suggested a habitat related species separation between E. argenteus and E. gula (Springer and Wood- burn 1960; Odum 1970), while another found little difference in the area of occurrence between these two species (Brook 1977).

Abundance data from the two collection sites studied suggested an interspecific habitat preference. Eucinostomus lefroyi was found almost exclusively in the inlet. Eu- cinostomus argenteus and E. jonesi were also captured more frequently in the inlet. Eu- cinostomus gula was taken more frequently from the Halodule station. A general occurrence pattern exhibited by the species found in both habitats showed that the smaller fish were more abundant in the seagrass site while the larger fish were more abundant in the inlet. It is suggested that habitat specific environmental parameters contributed to the observed size separation. Seagrass beds have also been well docu- mented as nursery grounds for a variety of marine species seeking adequate food re- sources and refuge from predation (Briggs and O’Connor 197 1; Zieman 1982).

In contrast to habitat selection, interspecific distinction in food types was not well defined. The diet of these mojarras was similar in composition to those reported in the feeding analyses by Carr and Adams (1973) and Brook (1977). Variations lie in the relative composition percentages reported in each investigation. Sand ingestion correlat- ed with bivalves and polychaete tissues and appeared to be inadvertently consumed. Changes in feeding have been attributed to habitat structure and relative food availability, varying as a factor of both spatial and seasonal fluctuations in prey density (Stoner 1980).

Slight changes in food composition between the two sites by the mojarras in this study appeared to be influenced by overall habitat structure. Distinction occurred primarily of inlet or seagrass sites rather than by species. Intraspecific variations in FO can be seen between the two major sites. Amphipod, bivalve, fish egg and isopod consumption was greatest in the inlet; co- pepod and nematode consumption was greatest in the grassbeds by each species (Table 3). Interspecific FO diet similarities also suggest a habitat influence on prey availability. Food preference may be an ad- ditional factor.

Intraspecific variation in diet was reflect- ed in an apparent ontogenetic feeding progression. The general pattern observed in each of the 4 species showed a transition from the consumption primarily of copepods and crustacean tissues in the smaller fish, to one which included a high percentage of polychaete tissues in the larger fish. Carr and Adams (1973) and Kinch (1979) found E. gula to exhibit the distinct transition from a planktivore, feeding on copepods, to a carnivore, feeding almost exclusively on polychaetes. Polychaete tissues represent a major dietary component throughout the range of individuals observed, increasing in importance with the growth of the fish. Due to mouth morphol- ogy, which limits the extent of substratum penetration, polychaete tissues found in the smaller specimens probably originated from prey captured in the water column (Dean 1979) or larval stages on the substratum surface.

322 B. A. Kerschner et al.

Die1 variation in feeding was evidenced in the feeding analyses. The mojarras studied exhibited an evening lcrepuscular feeding behavior. The high total gut content weight observed concurrently with a high frequency of empty guts in the evening specimens suggests either differential digestive rates of the prey items consumed or feeding on heavier items at dusk. Brook (1977) rec- ognized E. gula and E. argenteus as diurnal feeders but did not determine specific feeding periods during the day.

Mechanisms of resource partitioning, de- pendent upon variance through food type, habitat, and/or time allow the settlement of a great diversity of species (Schoener 1974; Livingston 1982). Although niche partitioning along the food resource dimension was not indicated by these data, slight interspecific differences of prey items were found. The inter- and intraspecific feeding behavior exhibited in this study was appar- ently an interrelationship of ontogenetic, spatial and temporal parameters. This is attributed to the utilization of available re- sources within the habitat structure.

ACKNOWLEDGMENTS

This research was supported by two research grants- in-aid from the Sebastian Inlet Tax District, Florida and the Florida Institute ofTechnology, and three grad- uate scholarships to Mark S. Peterson from the Slo- cum-Lunz Foundation of Charleston, South Carolina. We thank Michael Bodle, Elizabeth Cantrell, Robert Fricke and Brian Wendler for their aid in field collections. Thanks also to the many other people who as- sisted with field collections and in preparation of this manuscript.

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BERG, J. 1979. Discussionofmethodsofinvestigating the food of fishes, with reference to a preliminary study of the prey of Gobiusculus flavescens (Gobi- idae). Mar. Biol. 501263-273.

BRIGGS, P. T., AND J. S. O’CONNOR. 1971. Compar- ison of shore-zone fishes over naturally vegetated and sand filled bottoms in Great South Bay. N.Y. Fish Game 18:15-41.

BROOK, I. M. 1977. Trophic relationships in a seagrass community (Thalassia testudinum Konig) in Card Sound, Florida. Fish diets in relation to macro- benthic and cryptic fauna1 abundance. Trans. Am. Fish. Sot. 1061219-229.

CARR, W. E. S., AND C. A. ADAMS. 1973. Food habits

of juvenile marine fishes occupying seagrass beds in the estuarine zone near Crystal River, Florida. Trans. Am. Fish. Sot. 102:5 1 l-539.

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DEAN, D. 1979. The swimming ofbloodworms (Glyc- era spp.) at night, with comments on other species. Mar. Biol. 48199-104.

GILMORE, R. G., JR. 1977. Fishes of the Indian River lagoon and adjacent waters, Florida. Bull. Fla. State Museum Biol. Sci. 221101-147.

HYSLOP, E. J. 1980. Stomach content analysis-a re- view of methods and their application. J. Fish Biol. 17:41 l-429.

KINCH, J. C. 1979. Trophic habits of the juvenile fishes within artificial waterways-Marco Island, Florida. Contrib. Mar. Sci. 22~77-90.

LIVINGSTON, R. J. 1982. Trophic organization of fishes in a coastal seagrass system. Mar. Biol. 7: 1-12.

ODUM, W. E. 1970. Pathways of energy flow in a south Florida estuary. Ph.D. Dissertation, Univer- sity of Miami. 162 p.

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Received for consideration, December 5, 1984 Accepted for publication, June 6, 1985

ecotopic and ontogenetic trophic variation in mojarras...

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