Distribution and abundance of juvenile fishes along a salinity gradient in the Anclote River Estuary, Tarpon Springs, Florida

Distribution and abundance of juvenile fishes along a salinity gradient in the Anclote River Estuary, Tarpon Springs, Florida

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Distribution and abundance of juvenile fishes along a salinity gradient in the Anclote River Estuary, Tarpon Springs, Florida
Szedlmayer, Stephen T.
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Tampa, Florida
University of South Florida
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ix, 49 leaves : ill., map ; 29 cm.


Subjects / Keywords:
Fishes -- Florida -- Anclote River Estuary ( lcsh )
Fishes -- Geographical distribution ( lcsh )
Anclote River Estuary (Fla.) ( lcsh )
Dissertations, Academic -- Marine science -- Masters -- USF ( FTS )


General Note:
Thesis (M.S.)--University of South Florida, 1982. Bibliography: leaves 44-49.

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University of South Florida
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Universtity of South Florida
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All applicable rights reserved by the source institution and holding location.
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029683228 ( ALEPH )
09140010 ( OCLC )
F51-00018 ( USFLDC DOI )
f51.18 ( USFLDC Handle )

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DISTRIBUTION AND ABUNDANCE OF JUVENILE FISHES ALONG A SALINITY GRADIENT HI THE ANCLOTE RIVER ESTUARY, SPRINGS, FLORID/\ by Stephen T. Szedlmayer A thesis subnitted in partial of the for the degree of Master of Science in the Department of Marine Science in the University of South Florida 1982 Major Professor: John C. Briggs, Ph.D.


Graduate Council University of South Florida Tampa, Florida CERTIFICATE OF APPROVAL t1aster's Thesis This is. to certify that the t 1aster's Thesis of Stephen T. Szedlmayer with a major in Marine Science has been approved by the Examining Committee on February 26, 1982 as satisfactory for the thesis requirement for the Master of Science degree. Thesis Committee: Major Professor: John C. Briggs Member: Harold J. Humm Member: Joseph J. Torres


ACKNOVJLEDGEMENTS I am grateful to Drs. J. C. Briggs (chairman), H. J. Humm, and J. J. Torres for their helpful guidance and critical editing of the manuscript. Sincere appreciation is extended to the students of the Marine Science Department, University of South Florida, for their participation in field collections, especially M. Flock, B. Weigle, and F. Courtney. Lastly, I would like to thank my \vife for help in the computer work and typing of the manuscript. i i




LIST OF TABLES l. Total number of individuals and species collected at 18 sampling stations l, 2, and 3 Anclote River Estuary, Tarpon Springs, Fla. = Significance at 0.05 level, Wilcoxon signed rank test (Zar 1974). 2. Pooled species abundance for all collections at stations 19 l, 2, and 3 Anclote River Estuary, Tarpon Springs, Fla. Listed in order of abundance are species composing more than 0.1 % of the Percentage and standardized abundance per 400m are shown for comparison. 3. Percent of common species comparison with other studies 34 on the Anclote River 4. Two-way coincidence table comparing species clusters 37 with quantitative collection clusters. 5. Salinity tolerances of fish species collected in the 39 Anclote River Estuary, Tarpon Springs, Fla., based upon previous work. iv


LIST OF FIGURES 1. Anclote River Estuary, Tarpon Springs, Fla Station 7 1 was an estuarine area, station 2 was a tidal salt marsh area, and station 3 was a river area. 2. Species number vs. seine sweep, from station 1. Seine 10 sweeps were arranged in random order and graph lines were drawn by sight. 3. Species number vs. seine sweep, from station 2. Seine 11 sweeps were arranged in random order and graph lines were drawn by sight. 4. Species number vs. seine sweep, from station 3. Seine 12 sweeps were arranged in random order and graph lines were drawn by sight. 5. Salinity measurements from stations 1, 2, and 3 15 Anclote River Estuary, Tarpon Springs, Fla. 6. Temperature recorded from stations 1, 2, and 3 16 Anclote River Estuary, Tarpon Springs, Fla. 7. Standardized (#/400m2 ) of log transformed abundances 20 for selected species. Different letters denote significant change between stations, ANOVA, 0.05 level, Duncan's multiple range test (SAS 1979). 8. Mean size of selected species from different stations, 22 on the Anclote River Estuary. Size data were pooled for all collections for each station and species. The number of fish measured, station and of size are shown (bars with different letters are significantly different, 0 .05 level, ANOVA, Duncan's multiple range test, SAS 1979). 9. Menidia beryllina length frequency distribution, over 23 a salinity gradient: station 1, sal. = 22-34 ppt., station 2, sal = 6-25 ppt., and station 3, sal. = 2 -15 ppt. v


10. Dominance vs. the number of species from each 25 station. Community dominance index = lOO(A + B)/C, where A= most abundant species, B = the second most abundant species, and C = total abundance (Krebs 1978). 11. Quantitative analysis of collection similarity 26 (normal) of log transformed species abundance using Czekanowski's coefficient and group average sorting. A cluster group was considered as any group with a >50% similarity (fixed stopping, Boesch 1977). 12. Qualitative analysis of collection similarity 27 (normal) by presence absence criteria. Similarity = 2C/(A +B), where C =number of species in common, A= number of species in first collection and B= number of species in second collection. A cluster was considered as any with a greater than 50% similarity (fixed stopping, Boesch 1977). 13. Quantitative analysis of species co-occurrence 29 (inverse) of log transformed data by Czekanowski 's similarity coefficient and group average sorting. A cluster was considered as any group with a greater than 34% similarity (fixed stopping, Boesch 1977). vi


CISTRIBUTION AND ABUNDANCE OF JUVENILE FISHES ALONG A SALINITY GRADIENT THE ANCLOTE RIVER ESTUARY, TARPOrl SPRINGS, FLORIDA by Stephen T. Szedlmayer An Abstract Of a thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in the Department of Marine Science in the University of South Florida May, 1982 Major Professor: John C. Briggs, Ph.D. vii


ABSTRACT The relative importance of ocean spawned migrants in the juvenile fish population of the Anclote River Estuary, Tarpon Springs, Florida was determined by quantitative sampling of fish fauna along a salinity gradient. Three stations were established: station 1, an "estuarine" area (30 ppt); station 2, a "tidal salt marsh" (17 ppt); and station 3, a "river" area (7 ppt). Eight seine hauls were made bimonthly at each station with a fine mesh seine (1 .5 mm) from March to October, 1980 for a total of 16 visits per station. Statioh 1 was highest in total abundance, 4502 individuals/ 400m 2 and number of species, 37. Station 2, had one-fi fth the abundance of station 1, 857/400 m 2 and 23 species; station 3 had one-half the abundance of station 1, 2495/400 m 2 and 32 species. Stations \-Jere dominated by a few comiilOn species with most species low in abundance. Menidia beryllina (tidewater silverside), Anchoa mitchilli (bay anchovy), and Lagodon rhomboides (pinfish) made up 94% of station 1 's total catch. Anchoa mitchilli, beryllina, and Leiostomus xanthurus (spot) made up 84% of station 2 and 90% of station 3 in total catch. Dominance, m eas ured by the community dominance index (Krebs 1978), was positively related to species richness; as dominance increased richness increased. A succe ss ion pattern was o bser v e d, t hrough length frequency a nalysis, for five fish soecies: L. xanthurus, L. rhomboides, A. mitchilli, viii


Eucinostomus qula (silver jenny), and Fundulus grandis (Gulf killifish). The youngest members were found in low salinity waters, and moved to higher salinities as they grew. These ocean spawned migrants made up less than 23% of the total individuals of the Anclote River Estuary. The estuary and river stations are apparently discrete community habitats, while the tidal salt marsh is a transitional zone as indicated by presence-absence, abundance, and size data of the fish fauna. An increase in physical diversity of the habitat, mainly due to the presence of seagrass beds, is suggested as the principal factor affecting the distribution and abundance of fish fauna betvJeen sampling stations. The Anclote River Estuary serves as a nursery a rea for a fe\-J species of ocean spawned migrants but was dominated by resident species. Abstract approved: Major Professor Professor, Marine Science Date of Approval' ix


INTRODUCTION The nursery role of estuaries and rivers for larval and juvenile marine fishes has been studied in many areas north of the Florida peninsula (Bearden 1964; Thomas and Loesch 1970; Parker 1971; Herke 1971; Subrahmanyan and Drake 1975; Purvis 1976; Chao and Musick 1977; Weinstein 1980a). A successional pattern has emerqed in these studies in which the youngest members of several ocean spawned species initially take up residence in upper tidal creeks; then gradually move into higher salinities as they grow, leaving behind slow growing individuals and new recruits (Herke 1971; Dunham 1972; Purvis 1976). The relative importance of inshore migration by ocean spawned fishes, in the ecology of the estuary, is not clear from the literature. In North Inlet Estuary, South Carolina (Shenker and Dean 1979) and Cape Fear River, North Carolina (Weinstein 1980a), fish communities were numerically dominated by ocean spawned migrants. However, studies as the Shocum River, (Hoff 1977) and Patuxent Estuary, Maryland (McErlean et al. 1973) showed that resident fish species were numerically dominant. Few studies of this nature have been conducted on the west coast of Florida (Subrahmanyan et al. 1975; Weinstein et al. 1977), and the relative importance of transient versus resident fish in the estuary is still unresolved. Consideration of this problem was addressed in the present study by sampling the juvenile fish


fauna of the Anclote River Estuary, Tarpon Springs, Florida. The study site was chosen because of its relatively abrupt salinity change (marine to low salinity water in a distance of 9 km) and the fact that no studies have sampled the juvenile fishes along its salinity gradient. The purpose of the present work was 1), determine the relative importance of marine spawned fishes inhabiting the low salinity 2 areas 2), evaluate a successional pattern if it exists 3), investigate the fish community found along the salinity gradient of the Anclote River Estuary, quantitatively.


LITERATURE REVIEW Estuarine and adjacent low salinity areas have been identified as nursery areas for ocean spawned larval and juvenile fishes (Purvis 1976). In particular, Bearden (1964) showed that Micropogon undulatus, the Atlantic croaker, spawned several offshore. After hatching, larvae spent their first days at sea; subsequently, the main body of young croakers moved up tidal creeks into areas of reduced salinity, and as growth proceeded they gradually moved seaward again. Other fish species have shown a similar life cycle: Urophycis regius, the spotted hake; Cynoscion regalis, the weakfish; Bairdiella chrysura, the silver perch; xanthurus, the spot; and Lagodon rhomboides, the pinfish (Hansen 1969; Parker 1971; Markle 1976; l979a). While the nursery role of estuaries and low salinity areas is apparent, the relative importance of ocean spawned migrants in the low salinity area is vague. In North Inlet Estuary, South Carolina, 70% of the total number of fishes were transients: Leiostomus xanthurus; sp.; ounctatus_, the speckled worm eel; Lagodon rhomboides; Paralichthys sp.; and undulatus, while about 25% were permanent residents: Menidia menidia, the Atlantic silverside; Anchoa mitchilli, the bay anchovy; Fundulus sp., as vJell as several gobies (Shenker and Dean 1979). 3


(l980a) found a similar fish community in the Cape Fear River, rlorth Carolina. Transient species vJere dominant and included: Leiostomus xanthurus; Mugil cephalus, the striped mullet; and Brevoortia tyrannus, the Atlantic menhaden. The permanent residents, although common, were second in abundance compared to transients and included: Anchoa mitchilli; Fundulus sp.; Mendia menidia; and Eucinostomus argenteus the silver jenny. Other investigators of fish communities in estuaries report that resident fish species were the numerical dominants. Hoff 4 (1977) showed that Buzzards Bay, Mass. was dominated by the resident fishes: Fundulus heteroclitus, the mummichog, and Menidia menidia. McErlean et al. (1973) sampled th e Patuxent Estuary, and also observed that Fundulus sp. and Menidia sp. were the shore dominants. Merriner et al. (1976) sampled the Piakatank River, Virginia and there again: Anchoa mitchilli; Trinectes maculatus, the hogchoker; and Bairdiella chrysura, all resident fishes, dominated the catches. On the west coast of Florida it is still unknown to what extent fishes use the estuaries as nur se ry grounds. Subrahmanyan et al. (1975) found that tidal creeks off Apalachee Bay, Fla. were dominated by transients, Leiostomus xanthurus and Lagodon rhomboides, while the adjacent Fenholloway River and Apalachicola Bay systems were dominated by resident s pecies (Livingston 1975, 1976). The Anclote River Estuary, also on the west coast of Florida, was repeatedly dominated by transient s pecies (Baird et al. 1971; Fable 1973; Rolfes 1974; Mayer and Maynard 1975; Thorhau g et al. 1977). Howe ver, these studies of the Anclot e concerned the fish


fauna in the high salinity areas ( ppt) and no studies have extended upriver into the low salinity waters. The present study details the composition of the nekton community in several low salinity areas. Quantitative distribution analyses of individual species and communities were compared through size frequencies and cluster analysis. Consideration is given to the role of these habitats as primary nurseries, and the relative importance of transients in the low salinity fish 5


STUDY AREA The Anclote River Estuary is a shallow, semi-enclosed, coastal embayment, located on the west-central Gulf coast of Florida betvJeen latitudes 28' 28l3'N and latitudes Sr47' (Fig. 1). Three station areas were established in the Anclote River and its estuary (Fig. 1). Station l, an 11estuarine11 area, salinity =30 ppt, was located at the mouth of the Anclote River and covered approximately 25 ha. The benthos at station l consisted of fine to medium quartz sand with scattered sandy clay deposits (Mohler 1963), and patches of seagrasses: Thalassia testudium, turtle grass; Syringodium filiforme, manatee grass; Diplanthera wrightii, shoal grass; Halophila engelmannii; and Ruppia maritima, widgeon grass (Humm et al. 1971). Thalassia, the most abundant species of seagrass at station l, grows below mean low water. Therefore, it was only sampled at low tides. Diplanthera, the second most abundant seagrass in the Anclote estuary station, grows in the lower intertidal zone and was sampled on every station visit. The estuary station also contained oyster bars, mangrove stands, and channels. Station 2, salinity ;:::;17 ppt, was a 11tidal salt marsh11 It was located 6.5 km from the mouth of the Anclote River and covered approximately 15 ha. Station 2 was characterized by sediments 6


GULF OF POWER PLANT I I TI\RPON SPRINGS l km u.s. 19 Figure l. Anclote River Tarpon Springs, Fla. Station l was an estuarine area, station 2 was a tidal salt marsh area,and station 3 was a river area.


grading from fine sand to clay mud deposits and was free of benthic vegetation. Shoreline vegetation of station 2 consisted of stands of Juncas roemerianus, the black rush. Station 3, salinity :::;7 ppt, a "riverine area" was located 9.6 km from the river mouth and covered approximately 10 ha. The bottom at the river station was mud to soft organic ooze without submerged benthic plants. Shoreline vegetation of the river area was characteristic of fresh waters and included Typha sp., cattails and Taxodium sp., cypress trees. 8


MATERIALS AND METHODS Field Salinity determinations were made with a refractometer and surface temperature vii th a hand-he 1 d mercury bulb therr1o meter. Specimens \'Jere collected v1ith a 1.5mm mesh 6.3 x 1.8m seine net with extra weights to improve its efficiency. A method of eight seine sweeps per station was adapted as a compromise between oversampling and undersampling species richness. This method was adequate for stations 2 and 3 but insuffecient for station 1 (Fig's. 2, 3, 4). Seine sweeps \vere made bi-monthly from 11arch to October, 1980 for a total of sixteen visits per station. On one occasion a station was missed: station 2, 9/18/80 due to weather. Sweep locations were chosen to maximize variation in physical characteristics (benthos type) and were random with respect to tidal condition s In the estuary area, three S\veeps \vere 1:1ade in the thick intertidal seagrass beds, three in a sheltered area of sand shell hash s ediment with intennittent sea9rass beds, and two in a Red mangrove-oyster bar area. At station 2, three sweeps were made in a narrow tida l creek three on the leeward side of a sandbar and two near a drop off. At station 3, o n e sweep was made next to a log jam, four along the sides of the river, and 9


10 5 0... (/) '+- 0 "'"" OJ > .,... 4 .jJ ttl ....-E u 10 5 4 10 5 8 10 5 8 Seine Sv1eeps 4 8 .. / ; I 10 Figure 2. Species number vs. seine sweep, from station 1. Seine sweeps were arranged i n random order and grap h lines were drawn by sight.


11 10 1 0 5 5 0.. Vl 40 '* Q) > .,.... 4 8 4 +J 8 tO ..-::::l E ::::l u 10 10 5 -, 5 4 8 4 8 Seine Sweeps Figure 3. Species number v s se ine s w eep, from statio n 2 Seine sweeps w e re arranged in random ord e r and graph lines were drawn by s i ght.


12 10 10 5 5 Q_ Vl '+--0 OJ > r--I-' 4 8 4 8 cd ..-2 u 10 10 5 5 4 8 4 8 Seine S'.'JeP.ps Figure 4 Species number vs. seine sweep, from station 3. Seine sweeps were arranged in random ord e r and graph l ines were drawn by sight.


three in a sheltered cove with soft organic substrate. The actual length of the seine net was 6.3 m but since a bow forms when the seine is used the effective length was approximately 4.5 m. The distance from shore was constant, 9.0 m (a transect line was used), thus the approximate area sampled per seine haul was 40 m 2 On some occasions the depth of water was too great for seining at a distance of 9.0 m from shore, and in these adjustments were made for calculation of area sampled based on actual measured distance from shore. Laboratory Specimens were stored in 10% formalin and brought back to the lab for identification and measurement. Random samples for size estimations of abundant species were obtained from each seine haul. The catch was homogeneously distributed over a grid then all those individuals in the first square, second square, and so on were used for size measurement until a maximum of twenty-five fish were measured. Rarer species necessitated the use of all specimens collected in a single haul to obtain size f r e quency data. 13


RESULTS Salinity and Temperature Salinity ranges were 22 -34 ppt at station 1, 6 -25 opt at station 2, and 2 -15 ppt at station 3. From March to October, 1980, the salinity gradient between stations 1, 2, and 3 always exceeded 4 ppt Synchronized fluctuations in salinity occurred at stations 2 and 3 (Fig 5). The lowest salinities recorded for stations 2 (6 ppt) and 3 (2 ppt) were in March with a steady increase to 25 ppt at station 2 and 15 ppt at station 3 in June. Salinities then declined to 14 ppt at station 2 and 5 ppt at station 3 in October (Fig. 5). Station 1 did not rigorously follow the pattern of salinity fluctuation seen at the other two stations. Station 1 's salinity fluctuated around 30 ppt from March to September, then dropped to 22 ppt with a quick return to 30 ppt in October (Fig. 5). In all three stations water temperature ranged from 23 C in early March to 35 C in July. There was little difference in temperature between stations in any one sampling period (Fig. 6). Abundance and Composition Station 1 showed the highest estimated abundance, 4502 individuals/400m2 and number of species, 37. Station 2 was lowest in abundance, 857/400 m 2 and number of species, 23. Station 14


30 Station l 25 +-' 20 Q_ Q_ >, +-' l 5 Station 2 r-c r-ru Vl l 0 5 Station 3 Mar. Apr. May Jun. Jul. Aug. Sept. Oct. Month 1980 Figure 5. Salinity measurements from stations l, 2, and 3 Anclote River Estuary, Tarpon Springs, Fla.


30 20 Station 3 10 30 u QJ 20 Station 2 1-:::::1 +-> ro 10 1-QJ 0. I=' (ij 1-30 20 Station 10 tlar. Apr. Jun. Jul. Aug. 1980 Oct. Sept Figure 6. Temperature recorded from stations l, 2, and 3 Anclote River Estuary, Tarpon Springs, Fla.


3 had intermediate abundance and number of species compared to other stations: 2495/400 m 2 and 32 species (Table 1). All three stations were dominated by a few common SDecies with most species low in abundance. Menidia beryllina, the tidewater silverside; Anchoa mitchilli; and Lagodon rhomboides made up 94% of the total fish catch for the estuary station. Anchoa mitchilli, beryllina, and Leiostomus xanthurus made up 84% of the salt marsh station and 90% of the river station in total catch (Table 2). Certain species showed significant differences in between stations, i.e., Fundulus simi lis, the longnose killifish; Eucinostomus Lagodon rhomboides; and Cyprinodon variegatus, the sheepshead minnow, had greater numbers at station l. Also Gobiosoma bosci, the naked goby; Microgobius aulosus, the clown goby; and Eucinostomus argenteus, the spotfin mojarra, had significantly greater numbers at stations 2 and 3. Menidia beryllina had greater numbers at stations and 3 (0.05 level, ANOVA, Duncan's multiple range test; Fig. 7). Figure 7 also shows that Poecillia latipinna, the sailfin molly, and Gambusia affinis, the mosquitofish, were collected mainly at the low salinity river station. Ubiquitous species that did not show significant differences in numbers between stations included: Mugil ceohalus; Leiostomus xanthurus; Syngnathus scovelli, the Gulf pipefish; Strongylura marina, the Atlantic needlefish; Fundulus grandis, the Gulf killifish; Oligoplites saurus, the leatherjacket; and Strongylura notata, the redfin needlefish. 17


Table l. Total number of individuals and species collected at sampling stations l, 2, anct 3 Anclote River Estuary, Tarpon Springs, Fla. *=Significance at 0.05 level, \Jilcoxon signed rank test (Zar 1974). I STATION I TOTAL NUMBER SIZE STANDARDIZED OF DAYS ABUN2ANCE! m SPECIES COLLECTED 400m l 56069 2 37 16 4502 4982 m 2 8155 2 23 l 5 857 3807 m I I I 3 I 21603 2 32 16 2495 3463 m co


T able 2. Pool e d species abundanc e for all collections at stations 1 2 and 3 Anclote River E stuary, Tarpon Springs, Fla. Listed in order of a b unda n ce are s p ec1es composing r1ore tha n of t h e total. Percentage and the standardized ab u ndance p e r 400 m 2 are s hown for co mpari son 1 il !Jif '1Uil;i.Jcr 1112 nunr!Jcr n 2 nw11br:r 1112 i1er", id-i"aber.YT1Tn a ____ 4 iois-83-:-9 -3"7 7sli\:-, i;itcO"f1TflT--I) 7Js s"?.-9 i 7 532 -m:zozs Anchoa mitchilli 3 1 56 5.6 253! L. xan t huru s 1 097 13. 5 115 1 L xanthurus 1221J 5. 7 141 L a')odon rhornboides 2323 4.2 1 871 M. beryllin a 102712.5 lOB fl.. mitchilli 572 2.6 66 L e i ostom u s xdnthurus 1004 1 3 81 1 1 i crogobius 367 4. 5 39 Gamilusia affinis 4B1 2 2 56 gu1 os us Cyprinod o n va ri ega tu s 909 1.6 73 E. arCJenteus 265 3.2 28 (i bosci 469 2 2 51) I alurevoortia Eucinoston:us gu1a 693 1.2 56 L. I'O I!lbO ides 209 2 6 378 1. 7 1)4 1 patronus Sardin e 1l a an c hovia 410 0.7 33 Gobiosoma bosci 165 2 0 1 7 L puvd 3 0 6 1. 4 3 5 L ucania parva 100 0. 2 B 1 cephal u s 13 9 1.7 1 5 E. a nJ e n teus 205 0 9 24 Eucinostom us ar

.+ N E 0 2.0 1.0 2.0 1.0 ........ en 0 t: <0 Q) 2.0 1.0 a Ul :::l <0 ..s:::: Cl. Q) u 0 (/) :::l +-' <0 01 Q) !.... <0 > u 2 3 Ul :::l !.... :::l ..s:::: +-' c: <0 X -l <0 +-' <0 +-' 0 t: (/) Ul :::l Q) +-' t: Q) 01 !.... a <0 2 3 .-Q) > 0 u Ul Ul :::l E Ul V1 :::l Ul 0 .-:::l 01 a a <0 c: .--<0 t: t: !.... <0 E <0 :::l 01 w Cl.. 2 3 Station 3 a b a Ul Q) "0 0 ..CJ. c:; 0 ..s:::: !.... u Ul 0 ..o a 1 2 3 ..s:::: u +-' ..... == Ul ..... -o t: <0 !.... en Ul .4-4<0 (.!) b b a 1 2 3 20 Figure 7. Standardized ( #/400m2) log transformed abundances for selected species. Different letters denote siqnificant change between stations, ANOVA, 0.05 level, Duncan's multiple range test (SAS 1979).


Significant differences in fish length were detected for a few species between stations, with the smallest size class generally found upriver in low salinity waters (0.05 level, ANOVA, Duncan's multiple range test; Fig. 8). Two species, Leiostomus xanth urus and Fundulus grandis, which were not significantly different in abundance between stations, did have significantly smaller classes at station 3. 21 Men1dia beryllina and Lagodon rhomboides both showed significant differences in fish length between all three stations. The largest specimens of tl beryllina = 45 mm) occurred at station 2, intermediate sized = 33 mm) at station l, and the smallest fish (i = 31 mm) frequented the farthest station from the Gulf, station 3 (Fig. 8). The largest specimens of .b_. rhomboides = 43 mm) vJere associated with station l, intermediates = 36 mm) wit h station 2, and small fish = 23 mm) with station 3. Young Gobiosoma bosci = 12 mm) frequented station 2, and Eucinostomus argenteus was not significantly different between areas sampled (Fig. 8). Anchoa mitchilli again demonstrat e d a smaller size class of fish at the upriver stations: station 3 = 20 mm), station 2 = 21 mm), and station l = 26 mm; Fig. G ). A detailed analysis of Menidia 8eryllina length frequency was possible because of its abundance In figure 9, a steady change in modal size frequency is seen for station l. As time orogresses from spring to fall, th e size classes shift from early juv eniles (20 mm) to juvenile -adult status (30-60 mm). Stations 2 and 3 shov1 a h 1 f1'sl1 s howin g peak abun1anc e in early different pattern, w1t arger


80 60 40 E E QJ N l/1 c 20 ro QJ ::?: Fig ure 8 Hear1 size of selected species from di fferent stations on the Anclote River Estuary Size data \ :ere pooled for al l collections for each station and species. The number of fish measured station and s ignificance of size are shown (bars with different are significantl y different, 0.05 level, ArJO'/A, Duncan's multip l e range test, SAS 1979). N N


1 3/26 4/09 soL 4/23 5/07 5/21 90 50 99 6/04 50 V1 QJ r-0.. iO V1 90 6 6/18 V1 7/02 50 QJ +-' ro "U "U 90 7/17 >,7/30 50 u t:: QJ ::l CJ QJ s... 490 ()-!< 8/13 50 8/30 9/18 9/25 90 1 50 10/10 10/24 90 50 50 90 STATION 2 50 90 Size mm 50 23 3 90 Figure 9. Menidia bery11ina lenoth frequency distribution, over a salinity gradient: station 1, sal.= 22-34 ppt., station 2 s al.= 6-25 ppt., and station 3, sal.= 2 1 5 ppt.


summer, increasing size through late summer, then decreasing again in early fall (Fig. 9). 24 Dominance of fish communities for the Anclote area was determined by comparing numbers of individual species. The percentage of total abundance contributed by t h e two most abundant species was used as a dominance index (Krebs 1978). Dominance was related to the number of species positively; as dominance increased, richness increased (Fig. 10). In qualitative cluster analysis of fish collections1 a stopping rule of greater than 50% similarity was used. This resulted in clusters forming according to spatial aspects rather than temporal criteria; i .e., estuarine station samples were clustered (group A), tidal salt marsh station samples were clustered {groups B, C), and river station sam ples were clustered {group D) with little tendency for monthly clusters (Czekanowski's similarity coefficient of log transformed abundances, average sorting cluster analysis, B oesch 1977; Fig. 11). Qualitative cluster analysis did reveal some grouping of estuarine and tidal salt marsh stations for the months of June, July, August, September, and October, but we also still see a strict spatial cluster for the river station, group U ([similarity = 2 ( # of species in common)/{# of species in the first group+ #of species in the second group)], Krebs 1978 ; average sorting cluster analysis, Boesch Fiq. 12). Since both quantitative and qualitative cluster analysis revealed spatial l. One collection= pooled sampl e s from each consecutiv e f our weeks: 2(8 seine hauls/day station).


80 X Q) -o c.: rQ) u c.: rO c 0 -o >, r-c.: :::> E 6 (._) Figure 10. estuary river tidal salt marsh 20 40 Number of species Dominance vs. the number of species for each station. Community dominance index = lOO(A + B)/C, where A = most abundant species, B = the second most abundant species, and C = total abundance (Krebs 1978). 25


C OLLECTION GROUPS A B c 0 E I I 1 I J_ 1 I 1 I J_ r-c 90 111 1 1 1112 3 2 2 2 2 2 2 2 3 3 3 3 3 3 3 Station tr Ar ty Jn Jl Ag Sp Ot Hr Ar Hy Jn Jl Ag Ot Sp My Jn J l Sp Ot Ag Ar Month Figure 11. Quantitative ana lysis of collection similarity (nomal) of log transformed species abundance using Czekanowski s coefficient and group average sorting. A c luster group was considered as any group \lith a> simi larity (fixed stopping, Boes c h 1 977)


50 90 u X y -I 1 l r-' -l-_._ T r--t-'l l l l 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 t lr Ar t ly Jn Ag Jl Ot Sp Jn Jl Sp Ag Ot Hr Ap tly f'ly Jn Jl O t Sp Ag t-11 Ar Station f lontt 1 Figure 1 2. Q u alitative analysis o f collection s i m i l arity (nor m a l ) by presen ce absence criteria. S i milarity= 2c/(a+b), where c =num ber o f spec i es in a = num ber o f s p ec i es i n t h e f irst collecti on, and b =number o f species in th e second collection. A cluster was considered as any with a greater than 50% s imilarity (fixed stoppi ng, Boesch 1977).


clusters, habitat effects were considered more important than temporal effects in determining the species composition of different stations. Quantitative species co-occurence cluster analysis (inverse), with a stopping rule of greater than 34% similarity, revealed 28 nineteen species groups. Seven groups had more than three species: groups 1, 3, 9, 11, 13, 16, and 19 (Czekanowski similarity coefficient with log transformed data, average sorting cluster analysis, Boesch 1977; Fig. 13).


%Similarity (.Jl 0 Paralichthys lethostigma S ymphurus plagiusa S y ngnathus louisianae i----------_jf------1 Anguilla rostrata t N Hippocampus zosterae t======j----, Bairdiella crysoura t======r----J w Hyporhamphus un ifac i a tus Chilomycterus schoepfi !' I Sphoeroides spengl eri """ Orthopristis chrysoptera t-------------, Dasyatis americana (.Jl I C) .._. ,00 Synodus foetens Paralichthys albigutta Trachinotus falcatus C y noscion nebulosus Fundulus similis Syngnathus scovelli Strongylura marina Fundulus grandis Oligoplites saurus Strongylura notata Eucinostomus gula Cyprinodon variegatus Lagodon rhomboides ttenidia beryllina Eucinostomus argenteus Anchoa mitchilli Sardinella anchovia -" Microgobius gulosus Gobiosoma bosci Lucania parva Gambusia affinis Poecilia latipinna Mugil cepha lus Leiostomus xanthurus Achirus lineatus t ti cropterus sa lmoi des Brevoortia patronus Lepomis sp. Rhinchthys sp. Ulaema lefroyi Lepisosteus sp. Lepomis macrochirus El ops sa urus undecimalis Opsanus beta Anchoa hepsetus Sphoeroides nephelus Opisthonema oglinum 0 l;;:; I ..,. I .._. OJ !;;:; w 0 w (.Jl Figure 13. Quantitative analysis of species co-occur rence (inverse) of log data by Czekanowski's similarity coefficient and group average sorting. A cluster was considered as any with a greater than 34% similarity (fixed stopping, Boesch 1977). '}!') '-


The nursery role of the Anclote River is apparently similar to other rivers. As has been found in other studies (Gunter 1957; Herke 1971; Dunham 1972; Harshall 1976; Chao and Husick 1977: Weinstein 1979a) the young of many species are found in low 30 salinity 1-'Jaters: Leiostor:1us xanthurus, Lagodon rhornboides, beryllina, Eucinostomus _gula, 1\nchoa nitchilli, and Fundulus in the present study (Fig. 8). fiO\Jever, in agreement with Hoff (1977) and McErlean et al. (1973) the equitability of these species indicates that the Anclote system i s dominated by permanent residents of the area rather than transients, that most incividuals stay in the immediate area for their entire life cycle as opposed to offshore migrations. The principal evidence that stations are doPlinated by permanent residents of the Anclote area comes from the size distribution and abundance data of Menidia Figure 9, indicates that is spawning somewhere in the Anclote River up from the estuarine station, because of the influx of new r ecruits seen at the tidal marsh station and river station in early and summer. If spawning occurred offs hor e 1 1ith larvoe and juvenile s subsequently moving into the area, v1e v10ulJ e x pect to see n e11 recruits at the estuary station: on th e contrary th e r e v1as no indication that spawning was offshore.


The conclusion that Menidia beryllina is spawning in the backwater s and not the open Gulf is supported by other studies (Lipp so n and r1oran lg74). The most compelling evidence that i1 b er'll_] j_0_9 i s a resident fish of the Anclote River Estuary is that adult fish (greater than 64 mm, Roessler 1970) "'ere caught at all stations . mitchilli, another fish in the Anclote, is also a tesident fish, because adults (greater than 34 mm, Stevenson 1958) \/ere caught and spa'lming v1as reported in harbors, estuaries, and s ounds (Dovel 1971). Other species that have been identified as inshore estuarine spawners in this and other studies include: parv_i, the raim1ater killifish; Gambusia affinis; Cy_p_rinqsl_2_ n yari_egatus; Gobiosoma bosci; and gulosus (Fanara 1964; Foster 1967; Dawson 1969; Fritzshe 1978; Hardy 1978a). The above species ate considered here as residents of tile Anclote systent and together make up of the total abundance for the estuarine station, for the tidal salt marsh station, and of the tiver station (Table 2). Other species that showed smaller size classes in the low salinity waters fit the role of transients in that the literature indicates they are offshore spawners: Lagodon Leiostomus xanthurus and Euc i nos tomus (Springer and Hood burn 1960; Parker 1971; Joseph 1972). Previous studies of the estuary station are not supported by the present study in that they indicate a general dominance by transient species (Table 3). Jl rhombo ides, cc_Rila 1 _l,_. xanthurus, and 1 t ri chodon, all transients, 111ade up 67"' of the total abundance (Fable 1973);


L_. r_honDJo_i_dr:_s, 62' of the total abundance (Throhaugh et a l. 1977); and L. rhoPib_o_i L. and G_. _ceplla 1 us 54;; 0 f the tot a 1 abundance in a 'Jtudj by 8aird et al. (1971). Hen: possible explanations for the dominance of 1enidiil b c _ljl_l_iD_

differences between present and previous studies (Table 3). Alteration of the Anclote environment through power plant construction and development could explain the dominance of permanent residents. Menidia beryllina might be an opportunistic species, i.e . rapid development, small size (Robbins 1969), and continuous reproduction (Tabb and Manning 1961); and as such has capitalized on the altered environment of the Anclote area. In studying 'the effects of a p01er plant on a t 1aryland estuary, McErlean et a 1. ( 1973) reported a change in fish fauna with migrating species becomming less common and a shift toward dominance by species. Livingston (1975) compared the polluted Fenholloway River and pristine Econfina system in northwest Florida. The ratio of residents to transients seen in the polluted Fenholloway River was approximately 1.3 to l, while in the unpolluted Econfina system a 1 to 1.1 ratio was seen. McErlean et al. (1973) suggested that the important function as nursery grounds for offshore spawners \'las being lost in the polluted estuary. The present fish comnunities on the Anclote could be indicative of a polluted environment, i.e . being dominated by resident species. The extensive seagrass beds located on the West Florida Shelf may also explain the dominance of residents observed in the Anclote system by serving as the primary nursery areas. and not the low salinity upper tidal creek areas. Other locations such as the Cape Fear River, H. C., where transient species dominated the estuary, are char acterized by a relatively short continental shelf (Shepard 1973; Smith 1976; Weinstein 1979a). Subrahmanyan 33


Table 3. Percent of co:nmon species co:nparison 1ith other studies on the ;inc1otc River. jFable 1973 I Thorhaug et al. 1977 i Baitd et al. 1971 1 rtesent study I I !-:-iL_a_g_o---.,.do-n----.4,-;:o-.-=o-tcrhorilbo i d _c_s _ ___ 62.-4--L. i=holiiho ide s40. o [ i dT,-i t 6 -1l ides 15.4 i Gobi osoma ------w-:-4--Tc. vdCi ;;qa tiiS' 9. 0 \li !!

and Drake (1975) in a study of a relatively pristine estuary, also adjacent to the West Florida Shelf, showed a dominance of residents similar to the present study. Thus, it may be that rivers adjacent to wide shelves with extensive seagrass beds are not influenced as much as other study areas by massive migrations of offshore fishes into estuary, tidal creek areas. The obvious next step would be to extend the present study out past the Anclote ancorage area, several km into the open Gulf of Mexico, and investigate the nursery role of seagrass beds found further offshore. An important ecological question concerning the area sampled is whether or not the stations sampled are discrete habitats or one homogeneous environment, throughout which fish species interchange freely. The common species: Leiostomus xanthurus, Mugil cephalus, Syngnathus scovelli, Strongylura marina, Fundulus grandis, Oligoplites saurus, and Strongylura notata generally treated all three collection areas, estuary, tidal salt marsh, and river as a continuum. Differences in abundance between stations were not significant for these fishes (Fig. 7). In contrast, other species: Nenidia beryllina, Fundulus similis, Eucinostomus Lagodon rhomboides, Cyprinodon variegatus, Eucinostomus arnenteus, Micro gobius gulosus, Poecilia latipinna, Gobiosoma bosci, and Gambusia affinis were either restricted to particular stations or had significant differences in population densities between the stations (Fig. 7). It may be concluded frolll distributional abundance that it depends on what species is considered, 35


36 whether or not discrete or continuous habitats were sampled. However, two species that did not sho\'1. preference for any of the stations through abundance data did segregate the stations by size: l xanthurus and f grandis (Fig. 8). The species showing size separat ion may be utilizing different food sources among the three areas, for Dietz (1976) has shown that the diets of several species found in the Anclote anchorage change with the of the fishes. Thus, spec ies not segregating in numbers may still indicate discrete habitats through size frequencies. Addi tional quantitative data analysis leads to a compromise between the discrete and continuum ideas. A two-way coincidence table illustrates a comparison of collection clusters (Fig. 11) with species clusters (Fig. 13) through total abundance (Table 4). Species groups 1, 3, 4, 5, 7, 8, 18, and 19 are essentially endemic to the estuarine area (cluster A). The river area (cluster D) was characterized by species clusters 11, 13, 15, 16, and 17. The tidal marsh area (clusters B and C) does not show any species groups endemic to the area and could be a transitional zone between the other b10 stations. Hence, the estuary and river stations appear to be discrete habitats while the tidal salt marsh is a transitional zone, but considerable amount of modification can be made on this general theme depending on the species considered. The greater richness observed at the estuarine and river stations compared to the tidal salt marsh has been reported in other geographical locations: North Carolina (Weinstein 1979a), South Africa (Day et al. 1952), and Florida (Wang et al. 1971;


Table 4. Two-way coincidence table comparing species clusters with quantitative collection clusters. _... Collection groups Species groups A B c 01 E I ; Patal ichthys lethostigma 1 2 ! I Symphurus plagiusa 5 2 Svnnnathus louisianae 3 I 2 Annu 1 11 a rostra ta 1 1 Hippocampus zosterae 2 i 3 Chilomycterus schoepfi I Bairdiella crysoura 2 I Hvporhamohus unifaciatus 3 J jpno eroldes soenoleri 23 I I 3 5 Orthopris tis c nrysop tera 5 0.1svat is arr.eri can a 1 I 6 Snodus foetens 4 3 1 : i Puallcht h s a lbiout ta 1 1 I ; 8 Trachinotus falcatus 14 1 1 1 I C1noscion nebulosus 4 i 1 Fundulus si milis 401 21 5 l Syn9nathus scovelli 38 19 3 Strongylura marina 35 3 8 7 Fundulus grandis 45 6 37 11 Oligopli tes saurus 54 13 11 Stronoylura notata 95 13 27 9 Eucinostomus gula 693 39 Cyprinodon variegatus 909 3 3 Lagodon 2328 219 3 Menidia beryllina 47018 682 401 17436 40 Eucinostomus argenteus 48 122 162 186 Anchoa mi tch i 1 I i 3156 4725 572 ]lSardlnella anchovia 410 5 Microgobius gulosus 3 2 365 134 Gobiosoma bosci 3 165 469 1 Lucania parva 10 8 298 Gambusia affinis 99 382 Poecil ia latininna 4 1 72 1 flug i I cepha 1 us 8 198 11 2 Leiostomus xanthurus 1004 2306 15 Achirus 1 ineatus 5 1 11 5 3 l licropterus salroides 2 25 6 Brevoortia Qatronus 1 377 4Lcpomis so. 4 l 1 5 Rhinichthys sp. 1 U1aema 1 efrovi 6 Lepisos teus sp. 1 1 6 Lepomis macrochirus 1 EloQS saurus 1 z Centrooomus 5 l !l Opsanus beta l Anchoa hepse tus 1 9 Sphoer oides nephe1us Olisthonema oolinum 5 Area i 4982 1782 2369 2673 446 37


Weinstein et al. 1977). Since these other geographical locations included a salinity gradient as well, the simplest explanation for the difference in species richness would be that the richness was salinity depende nt. Table 5 shows the salinity ranges of most of the species 38 sampled in this study and only five out of thirty-two would be considered s tenohaline: Trachinotus falcatus, the pennit; gulosus; Micropterus salmoides, the largemouth bass; Lepomis. macrochirus, the bluegill; and Opisthonema oglinum, the Atlantic thread herring. All other species in table 5 have been recorded in salinities greater than or less than the present study, or have been shown in experimental laboratory conditions to be able to tolerate greater ranges of salinity than normally encountered in nature. Thus, the fish species collected in the present study are probably not limited by the field salinities measured. To explain the greater richness at the estuary and river stations another theory, the "edge effect" has been described. In this theory estuarine areas fonn a mixing zone for euryhaline shelf and reef faunas while species composition upriver is influenced by freshwater faunas {Odum 1971; Weinstein 1979a). The existence of reef faunas {McHugh 1967) in the seagrass beds and its influence on species richness has been observed on the east coast of the U. s. and in areas where reefs are closely situated to the seagrass beds (Weinstein 1979a, 1979b). On the west coast of Florida a different biological and physical environment exists: extensive shallow shelf w aters have little depth gradient and reef habitats


Table 5. Salinity tolerances of fish species collected in the River Estuary, Tarpon Springs, Fla., based upon prev1ous work. Species Salinity tolerance Reference ranqe ppt Orthopristis. chrysoptera 0.0 -44.1 Johnson 1978 Bairdiella crysoura 0.0 48.0 II Trachinotus falcatus 23.0 -35.6 II II Cynoscion nebulosus 0.0 77.0 If Oligoplites saurus 0.0 -45.2 II Eucinostomus gula 0.1 -45.2 II Lagodon rhomboides 0.0 -44.5 II Eucinostomus argenteus 0.2 -45.2 II i Leiostomus xanthurus 0.0 60.0 II -;::----Syngnathus louisianae 0.0 45.0 Hardy 1978a I Hyporharnphus unifaciatus 7.5 -42.9 II Strongylura marina 0.0 -36.9 II Cyprinodon variegatus 20.0 142.4 II I -Lucania parva 0.0 -48.2 II Gambusia affinis 0.0 29.0 II M1cropterus salmoides 0.0 9.0 Hardy 1978b Leoomis macrochirus 0.0 13.0 II Symphurus plagiusa 0.0 42.9 Martin et al. 1978 Chilomycterus schoepfi 6.9 47.0 II I Sphoeroides speng1eri 9.7 38.8 II Menidia bery11ina 0.0 75.0 II Muqil cepha 1 us 0.0 81.0 II Hippocampus zosterae 9.7 35.0 Springer et al. 1960 Achirus lineatus 4.0 34.6 II beta 3.2 45.2 II Synodus foetens 4.0 60.0 Jones etal.l978 mitchi11i 0.0 80.0 II Elops saurus 0.2 36.0 II Anchoa hepsetus 2.5 80.0 II Opisthonema oqlinum 32.0 43.0 II rMicrogobius gulosus 10.0 35.0 Fritzsche 1978 0.1 45.0 II Gobiosoma bosci -39


are generally found greater than 11 km offshore, with the most complex existing about 141 offshore (Smith" l976). In addition, seagrass studies on Florida's west coast, such as those in the area /" east of Panama City (Caldwell 1954) and Tampa Bay (Springer et al. 1960) indicate that seasonal recruitment of tropical reef species does not occur to any large extent. The present work also shows a lack of shelf and reef species. Therefore, some other mechanism must be operating which would result in greater species richness at the estuary station. In contrast, the edge effect model may fit the river station of the Anclote where immigration from fresh water has occurred: lepomis sp., Micropterus salmoides, and lepisosteus sp. were observed on occasion (Table 4). Another explanation for the greater species richness observed at the estuary and river stations, although similar to the edge effect, is that of spatial heterogeneity (MacArthur and MacArthur 1961). The difference between the spatial heterogeneity theory and the edge effect is that the former would not rely on immigration from reef or shelf fishes. The spatial heterogeneity theory suggests that a greater physical diversity will increase niches and refuges; consequently, more species can survive in that habitat. Extensive seagrass beds intermingled with channels, sand shell 40 areas, oyster bars, and mangrove stands probably create a more diverse physical habitat at station 1 compared to the other stations, resulting in a greater species richness. The river station, second in species richness, qualitatively is second in physical heterogeneity due to cattails, trees, shoals, and fallen debris


but without benthic vegetation. The tidal salt marsh showed the lowest species richness and was also the lowest in physical diversity, characterized simply by black rush stands and algal mud bottoms. Evidence that physical differences are more important than temporal criteria or month of collection in explaining the fish distribution observed comes from the quantitative and qualitative of collections (Figs. 12, 13). The spatial aspect clustered almost exclusively in the quantitative analysis and in about half the cases for the qualitative analysis. Therefore, with grouping primarily according to habitats and the qualitative difference in physical aspects, the spatial h eterogeneity theory is a workable model for explaining the richness differences between stations in the Anclote River. Considering the evenness component of the fish divers ity, it was surprising to observe a decrease in evenness as the richness increased (evenness indicated by the dominance index: the greater the dominance, the lower the evenness; Fig. 10). Precisely the opposite has been observed in many different ecological systems: in invertebrate communities of decaying oak logs (Fager 1968), annual grasslands (McNaughton 1968), polychaetous annelids (Santos and Simon 1974), and fish communities (Marshall 1976; Weinstein 1979a). However, another study concerning fish colilmunities on the west coast of Florida has observed the same phenomenon. In Marco Island, seagrass stations had a greater degree of dominance concurrent with maximum numbers of spe cies compared to sand areas 41


( \/Pi n <;t

43 COI!CLUSIOf'lS l. A successional pattern was observed for some fish species on the Anclote River Estuary, Fla., with the youngest members found in low 5alinity waters and moving to higher salinities as they grew. The majority of individuals are not ocean spawned migrants, but permanent residents of the area. Possible explanations for the apparent dominance of permanent resident fish species compared to a dominance by transients in other studies include: gear sampling bias, alteration of the Anclote environment with concomitant faunal change, or that seagrass beds further offshore may be serving as the primary nursery areas for most ocean spawned fishes, but further work in these seagrasses is needed to affirm such a hypothesis 2. The estuary and river stations on the Anclote system are apparently discrete community habitats The tidal salt marsh station appears as a transitional zone; as indicated by presence absence, abundance, and size frequency data of the fish fauna; but this theme may be modified depending on the species under consideration. 3. Spatial heterogeneity differences mainly due to the existence of seagrass es is suggested as th e principle factor affecting th e distribution and of f i s h f auna in t h e /\nclote River Estuary


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