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BULLETIN OF MARINE SCIENCE, 46(1): 3-12, 1990 ONTOGENY AND OVERLAP IN THE DIETS OF FOUR TROPICAL CALLINECTES SPECIES Allan W Stoner and Beverly A. Buchanan ABSTRACT The diets offour Callinecles spp., Portunidae, from a small tropical lagoon were examined for ontogenetic and interspecific variation. The primary food organisms were crabs, fishes, shrimp, amphipods, bivalves, and polychaetes; but the relative importance of each varied greatly with crab species and size. Callinectes danae had the least varied diet, relatively low proportions of detritus and consumed mostly large motile prey suggesting a diet more predacious than the other three species. Callinectes sapidus had a highly diversified diet with three primary feeding types ontogenetically. Callinectes bocourti showed considerable dietary overlap with C. sapidus, and Callinectes omalus demonstrated greatest ontogenetic variation. Crabs of small size classes showed greatest interspecific variation within comparable size classes. Dietary diversity was also greatest in small crabs and least in the largest size classes, while prey size, in terms of kind of prey, increased with crab size. Overall, few strong similarities occurred either within a species or between comparable size classes of different species. This suggests that the incorporation of size and species specific trophic information may be necessary for an understanding of community or ecosystem structure even when considering closely related species. Swimming crabs of the family Portunidae are abundant in coastal and estuarine waters of temperate and tropical regions, particularly where wetland habitats provide abundant food and shelter for the crabs and their young (Tagatz, 1968; Norse, 1978). Because of the commercial significance of Callinectes sapidus, its food habits have been examined in detail. The species was originally described as a scavenger and cannibal (Hay, 1905), but has since been shown to consume a wide variety of living organisms including crabs, shrimp, molluscs, fishes, and polychaetes (Darnell, 1958; Tagatz, 1968). Laughlin's (1982) thorough investigation of C. sapidus in Apalachicola Bay, Florida, showed diets varied with crab size, season, and location. Field and laboratory studies have confirmed that C. sapidus selects particular prey species as well as prey sizes, and that the crabs mediate prey population structure in certain cases (Hamilton, 1976; Hughes and Seed, 1981; Blundon and Kennedy, 1982; Kneib, 1982; West and Williams, 1986). The only other Callinectes spp. examined for diets, C. arcuatus and C. toxotes in the Huizache-Caimanero lagoon of western Mexico, showed seasonal and spatial as well as some interspecific variation in feeding ecology (Paul, 1981). The sizerelated differences in diets generally agreed with those found for C. sapidus (Laughlin, 1982). In this study, we characterize intra- and interspecific variation in the diets of a guild of four sympatric Callinectes spp. in a tropical estuary of Puerto Rico. Where possible, temporal variation in diets were examined and related to prey abundance. MATERIALS AND METHODS Callinectes spp. were collected monthly over a two-year period, from September 1984 through August 1986, at five stations in Laguna Joyuda, Puerto Rico. The lagoon, previously described by Buchanan and Stoner (1988), is a mangrove-fringed, polyhaline system, characterized by a relatively homogeneous mud bottom. Submerged vegetation (Thalassia testudinum) is limited to small patches near the inlet and in the north section of the lagoon. 3 4 BULLETIN OF MARINE SCIENCE, VOL. 46, NO. I, 1990 Table I. List of the general food categories used for stomach contents of Ca//inectes spp. and the codes employed in food habit histograms Code Food category AM BA BI CC CR CyC DE FO FR GA HC IE Amphipod Barnacle Bivalve Calanoid copepod Crab Cyclopoid copepods Detritus Foraminifera Fish remains Gastropod Harpacticoid copepod Invertebrate egg • Miscellaneous-used Code MI· NE OS PM PO PP RU SA SH TA TH Food category Miscellaneous Nematode Ostracod Plant material Polychaete Penaeus postlarvae Ruppia Sand Shrimp Tanaid Thalassia in food histograms for all above food categories making up <3% of the total mass. A 5-m semiballoon otter trawl with 2.5-cm mesh panels and a 5-mm mesh cod-end liner was used for collecting crabs. The net was towed with a small skiff at 2.5 knots for 70 m, and six replicate tows were made at each station. The majority of the crabs had food in their guts because of crepuscular feeding activities in Ca//inectes spp. (Ryer, 1987). All shrimp, fish, and crabs were preserved in 10% formaldehyde diluted with lagoon water. Later, all crabs were identified to species when possible, counted, measured (carapace width, including the lateral spines), and transferred to 70% ethanol. Identifications were made using Williams (1974). Analyses of distribution and abundance patterns were reported by Buchanan and Stoner (1988). Numbers of crabs collected at each station were low; therefore, animals of individual size classes and species were combined for individual dates or sets of dates. This is justified for several reasons: I) All of the Ca//inectes spp. (except C. ornatus) were found at all stations (Buchanan and Stoner, 1988). 2) The lagoon is small (only 1.2 km2 in total surface area) and Callinectes spp. are highly mobile. 3) The composition of prey species is relatively homogeneous in Laguna Joyuda (Stoner, 1986; 1988; Stoner and Acevedo, in press). Important macrofaunal prey species such as Dasybranchus lumbricoides, Capitella capitata, Grandidierella bonnieroides. and Macoma brevifrom were abundant and had similar biomass composition at the different stations, Crab foreguts were pooled by individual species and size class, and preserved in 70% ethanol with dilute rose bengal stain. Except for C. sapidus, crabs under 20 mm carapace width (CW) could not be identified to species, and were omitted from the analysis. Crabs of 20-40 mm CW were divided by species into 10-mm size classes, and crabs over 100 mm CW into 25-mm size classes. The gravimetric sieve fractionation procedure (Carr and Adams, 1972) was used to analyze foregut contents. The method is particularly useful in examining the diets of crustaceans (Leber, 1985) and has been used with C. sapidus (Laughlin, 1982). With two exceptions, all food particles were placed in mutually exclusive general categories for statistical treatment (Table I). Categories such as amphipod, Foraminifera, and nematode were employed. The categories "animal remains" (unidentified tissue stained with rose bengal) and "plant remains" were the only food categories that were not mutually exclusive from other groups. "Animal remains" was not utilized since it would bias the analysis. The low number of prey species in the lagoon precluded the possibility that there was an unknown prey which was not identified, and over 70% of the "animal remains" came from the smaller sieve sizes indicating that they were particles from already identified prey. "Detritus" was material not stained by rose bengal and lacking the pigments of living algae or seagrasses. Most of the material identified as detritus was brown and contained the fibrous material of vascular plants, primarily mangroves. Whenever possible, more specific information, such as the genus or species of food items, was recorded, Similarities in diet between the various species and size classes were measured with Czekanowski's coefficient (Bray and Curtis, 1957; Field and McFarlane, 1968) using proportions of foods of each type. Dendrograms were constructed from the similarity matrices using average linkage classification. Dietary diversity for each size class was calculated, using the Shannon-Weaver diversity index (H' = p; log p.). Where crabs were sufficiently abundant to examine temporal variation in diets, comparisons with prey abundance were made. For this purpose, two measurements of prey abundance were used: I) total number of penaeid shrimps per trawl, and 2) total number of anchovies (Engraulidae) and mojarras (Gerreidae) per trawl. These two fish families comprised the majority of fishes in the crab diets. STONER AND BUCHANAN: CALLINECTES 5 SPP. DIETS Table 2. Proportion of crabs for each species and size class with food in guts (% WF) and the proportion of unidentified animal remains (% AR) in the gut contents e. sapidus e. danae Size 10-20 21-30 31-40 41-60 61-80 81-100 101-125 126-150 X %WF 82 83 80 64 83 78 88 79.7 %AR 10.4 6.8 4.6 3.1 4.0 2.8 2.4 4.8 %WF %AR 92 72 82 87 83 70 94 68 81 17.4 13.5 21.5 14 12.4 9.1 11.5 6.7 13.3 e. bocourti C. ornatus %WF %AR %WF %AR 77 92 100 87 88 11.9 13.8 13.1 7.3 2.8 92 67 83 64 50 75 16.6 13.1 15.2 3.2 5.7 8.6 71.8 10.4 88.8 9.8 RESULTS Five-hundred thirty-six crabs were examined for gut contents of which 475 (80%) contained food items. The proportion of crabs with gut contents varied between species and size classes, as did the proportions of "animal remains" which were excluded from the analysis (Table 2). In general, however, more than 50% of the animals in all species and size classes had food in the guts, and unidentified "animal remains" made up less than 20% of the gut contents in all but one case. Dietary components varied both between species and size classes, but the most common dietary items for the crabs were fish, detritus, crabs, and bivalves. Other prey such as amphipods, polychaetes, shrimp, and gastropods also made up measurable amounts of food weight in some size classes or species. Size classes were clustered first within each species. Many natural clusters of size classes were apparent at the 0.6 level of similarity (Fig. 1). Callinectes danae showed the least ontogenetic variation in diets; all C. danae between 20 and 125 mm CW formed a separate group. Dietary items of greatest weight in the 21-125-mm size classes were crabs (mostly hermit crabs) which were less important in the 126-150-mm size class. Fish weight increased from the smaller to the larger size groups; and shrimp increased gradually over the size classes within the first size group, then decreased to less than 2% in the 126-150mm crabs. Relatively little detritus was found in C. danae. Less important food groups such as amphipods and gastropods generally decreased in weight with increasing crab size. Dissimilarity between the largest size class and the others was related to a high proportion of bivalves in the larger crabs. Callinectes sapidus clustered into four major groups from the original 8 size classes: 10-20,21-30,31-80, and 81-150 mm CWo The two smallest size classes were different from each other and other size classes, both in the major constituents and the proportions. Amphipods which were major dietary constituents in the 10-20-mm crabs and foraminiferans which were important in the 21-30-mm crabs, were rare or absent in diets of larger crabs. Polychaetes decreased in diets with increasing crab size. Detritus, important in the smaller size groups, had less weight in crabs over 80 mm CWo Crab and fish remains were important dietary items in crabs above 30 mm CWo Bivalves occurred in 31-80-mm crabs, and were uncommon, except in the 81-150-mm crabs. Callinectes ornatus clustered into three major groups: 21-30, 31-80, and 81100 mm CWo Detritus and shrimp decreased in weight with crab size. Bivalves and gastropods were absent in the smallest size group and increased with crab size. The high proportion of amphipods and low proportions of fish and crabs in 6 BULLETIN OF MARINE SCIENCE, VOL. 46, NO.1, JI 21-30 :B (18) 31-40 :B (10) c: 61-80 81-100 41-60 ro 100·125 (/) Q) 13 Q) u 1990 (27) (35) (16) :B Iffl~~(14) . TI 126-150 ~ (7), I . I • I • I - o o en (Xl 0 ~ 0 N 10-20 :B 21-30 ~ (") (/) Cl) w U < 0< a: < u o z < ct) w u W 0- 13 Q) c ctl U 31-40 61·80 41-60 8HOO 100-125 126-150 (3 21-30 I •I • I •I :B ~ (10) (23) J~ (38) r;: 31-40 61-80 :B 41-60 j:J 81-100 ~I__ .~ --.- ct) 0 0 0 (Xl en ~ ~ ~(26) m .-~ o J~I ffl G) m (7). '~ I • I • I • I !=> 000 m ~ ~ (Xl j:J 21-30 (11) (8) (20) 31-40 41-60 61-80 (9) (10) 8HOO (6) 100·125 •...• N 000000 W ~ U1 en o I ••••••• (Xl o 0 to o 0 0 • I ? I I • I . I 000 m ~ ~ (N) SIMilARITY (Xl FOOD ITEMS (%) Figure 1. Diets of four Callinectes species in Laguna Joyuda, Puerto Rico, shown as a function of crab size. Food categories are identified in Table I, and striped areas represent miscellaneous (MI). The similarity index in the cluster diagrams in Czekanowski's coefficient. the smallest and largest size groups, respectively, contributed to the differences in clustering between these and the intermediate sized crabs. Callinectes bocourti clustered into four major groups: 21-60, 61-80, 81-100, and 101-125 mm CWo The proportions of crab remains (mostly hermit crabs and some Callinectes spp.) and detritus decreased with increasing size, while fish remains increased in weight with crab size. Polychaetes were common in the STONER AND BUCHANAN: C.S. 10-20 C.S. 21·30 C.O. 21-30 7 CALLINECTES SPP. DIETS ,..........................................• jC.S. 41-601 L9..:~.: ~.~.:..~.~g..l C.b. 21-30 C.S. 31-40 .s- C.b. 41-60 CI) C.b. 31-40 C.S. 61-80 •....................•.................. E I I- o ......................................... C.d. 21-30 w !..C·:ti..·..·..·..31·~40·1 (L <{ I c.s. 81-100 ~ o <{ ex: <{ o o z <{ CI) W o W 0.. i :: ! C.d. I C.d. I C.d. 61-80 i ! I 41-60 I 1..9..:~.:.....~..?~.~. .~.~.~..i c.o. 41-60 I..C·~S·:..··1·0r·1·25·1 81-100 CI) L.~.:.~.: ..... ~.~.~.:.~.~gj C.o. 31-40 C.O. 61-80 ........................................... I I [,.~. .:~.: ~~.~~?.J C.d. 126-150 C.o. 81-100 C.b. 101-125 1.0 0.8 0.6 0.4 0.2 0.0 I I I I I SIMilARITY Figure 2. Cluster diagram for the diets of crabs incorporating all species and size classes. Cluster strategy is the same as that in Figure I. e.d. = Cal/inectes danae. e.s. = C. sapidus, e.o. = C. ornatus, e.b. = C. bocourti. smaller size groups, though quite variable, and absent in the 61-80-mm size class. Bivalves, although highly variable in contribution to food weight, were present in most classes. Dietary differences among both species and size classes were examined by entering all data on all original size classes and species into a cluster analysis (Fig. 2). Consistent with the initial cluster analysis, C. danae showed the greatest ten- 8 BULLETIN OF MARINE SCIENCE, VOL. 46, NO. I, 1990 dency to cluster intraspecifically with all but the largest (> 125 mm) and smallest (21-30 mm) size classes grouping at a similarity of 0.73 along with C. sapidus of 81-100 mm. This was due to similar high proportions of crabs, shrimps, and fish in the diets. Callinectes sapidus of 101-125 and 126-150 mm clustered at a similarity of 0.7 largely due to high proportions of crabs and bivalves, and these clustered less strongly (0.6 similarity) with C. danae of 31-125 mm because of high proportions of crabs in the diets. Callinectes bocourti from 31-60 mm grouped with C. sapidus of 31-40 mm and 61-80 mm at a similarity of O. 7, due to similar proportions of crabs, detritus, and polychaetes. Callinectes bocourti of 81-100 mm also grouped with C. sapidus of 41-60 mm in a separate grouping at the 0.7 level because of high proportions of polychaetes, fish, and bivalves in this group. Callinectes bocourti of61-80 mm grouped with C. ornatus of61-80 mm (similarity of 0.76) largely due to high proportions of bivalves and gastropods, and C. ornatus of 31-40 mm further grouped with these two at a similarity of 0.7. The largest C. danae (126-150 mm) clustered less strongly (0.63) with the previously mentioned C. bocourti-C. ornatus complex because of a high percentage of bivalves. The largest size classes of C. ornatus and C. bocourti differed from all other groups; the largest C. bocourti had an extraordinarily high proportion of fish in the guts (73%). There was a tendency for the smallest size classes of all species to show relatively low similarities (0.7) with other size classes of the same species or with each other. In particular, C. sapidus of 10-30 mm and C. ornatus of 20-30 mm grouped with no other size classes or species above a similarity of 0.5. Where similarities of greater than 0.6 did occur in small size classes (such as with C. danae and C. bocourtl), it was with other size classes of the same species rather than between species. The high degree of dissimilarity between different species of small crabs is due to a greater overall diversity in the types of food items consumed, such that major prey groups differed. Small prey such as amphipods, forams, invertebrate eggs, and polychaetes became important in different species. The diversity indices (Table 3) for all small, 21-30-mm CW, crabs were high compared with the diversity indices for the individual species of that size, indicating again that different species of small crabs utilized different food items. Diversity indices for the largest crabs of each species were all lower than the diversity indices for other size classes of the same species. Callinectes danae tended to have the lowest dietary diversity, but species differences were not large. Species and genus identifications of prey items indicated no obvious differences occurred between species or size classes except that remains of Callinectes spp. occurred in large C. danae. Fish remains were rarely identifiable; the only ones identified being Anchoa spp. and juvenile mojarra (Gerreidae). Shrimp (Penaeus spp.), crabs (hermit crabs with a few incidences of Callinectes spp. and xanthids), bivalves (mostly Macoma spp.), gastropods (all Nerita spp.), polychaetes (Dasybranchus /umbricoides or other capitellids), amphipods (all Grandidierella bonnieroides), and calanoid cope pods (Acartia tonsa with some Pseudodiaptomas spp.) were all identifiable in the gut contents of Callinectes spp. examined. Crabs were sufficiently abundant in only one trophic group (c. danae, 31-125 mm, plus C. sapidus, 81-100 mm) to provide a seasonal analysis of diets (Fig. 3). Detritus and crabs showed relatively little variation over time in the diets. On the other hand, a switch from fish to shrimp was in evidence over the study period. Fish comprised 40% of the diets in the fall quarter (October, November, December) and shrimp comprised 33% of the diets in the winter (January, February, March). Dietary switching was associated with high abundance of anchovies and mojarras from July to December, and high abundance of shrimps between February and June. STONER AND BUCHANAN: CALLINECTES SPP. DIETS Table 3. Dietary diversity in Callinectes species from Laguna Joyuda, Puerto Rico, by size class. Values are Shannon-Weaver indices (H') Carapace width (mm) Callinecles danae Cailinectes sapidus 1.66 1.49 1.79 1.45 1.59 1.54 1.29 1.37 1.90 1.58 1.96 1.91 1.64 1.64 1.35 10-20 21-30 31-40 41-60 61-80 81-100 101-125 126-150 Ca/linectes ornalUS 1.80 1.95 1.82 1.93 1.63 Callinectes bocourti All species 1.52 1.35 1.45 1.86 1.93 0.88 2.17 1.89 2.00 1.99 2.23 1.79 1.44 DISCUSSION The dietary habits of Callinectes spp. in Laguna Joyuda differed strongly between size classes and species, though there were more apparent similarities between species than size classes. The smaller size classes of each species were ;? o - Cf) I- Z 100 90 W I- 60 50 o (.) 40 Z I- ~ CJ DE 80 70 CR 30 20 10 o J ASONDJ FMAMJJ 40 30 .....J 3: « a: I- ........... 0 SHRIMP FISH s: m • 30 20 -.... a.. ~ 11 U> 20 :r: a: I Cf) Z 10 10 « w ~ » z -- -I JJ » :E 0- .•0····0'······ r o a JASON DJ F MAMJ J MONTHS Figure 3. The top graph illustrates seasonal gut contents for C. danae 31-125 mm CW and C. sapidus 81-100 mm CW. The bottom graph shows seasonal abundances of shrimp and fish (Engraulidae and Gerreidae). Vertical bars represent standard errors for all replicates and stations. 10 BULLETIN OF MARINE SCIENCE, VOL. 46, NO. I, 1990 . particularly dissimilar, with each species having at least one different major prey group. In contrast, Laughlin (1982) found some very high similarities (>0.8) among size classes of C. sapidus. In general, plant material and detritus intake decreased whiie shrimp, fish, and bivalve intake increased with crab size. Similar results were found for two Pacific Callinectes species (Paul, 1981) and for C. sapidus in Florida (Laughlin, 1982), with the differences in major constituents being explained by differences in available prey types between areas. Bivalves, which are not abundant in Laguna Joyuda (Stoner and Acevedo, in press) are abundant in Apalachicola Bay and formed the highest percentage of the diets in all size classes of C. sapidus examined by Laughlin (1982). Callinectes danae in Laguna Joyuda demonstrated the least ontogenetic variation in diet, relatively low proportions of detritus, high amounts of animal material, and occasional cannibalism. This did suggest that C. danae are capable of handling larger and more motile prey. Callinectes ornatus exhibited the greatest dissimilarity in diet ontogenetically and had a relatively high diversity of prey items. Somewhat analogous to C. danae, observations on C. toxotes in the Pacific though limited suggested that the species was more predacious and the diet less varied than that of C. arcuatus (Paul, 1981). The similarities in food habits we found between C. sapidus and C. bocourti may reflect morphological differences from the other Callinectes spp. in ability to capture or handle different food types because they are thought to be more closely related to each other than to the other two Callinectes spp. (Norse and Fox-Norse, 1979). Great variation in Callinectes feeding behavior has been documented in earlier studies. An examination of foraging strategies of C. sapidus in Alabama Spartina marshes showed distinct preferences for particular size classes of some visual (epifaunal) prey such as Littorina and fish, but little size-selective preference for infaunal prey such as the mussel, Geukensia sp. (West and Williams, 1986). Additionally, prey species shifted with manipulations of overall prey density, as we noted with our seasonal data. As opposed to C. sapidus, C. danae and C. ornatus are known to be relatively oceanic in distribution (Norse, 1978), probably living in clearer waters, and thus may have evolved more visually oriented feeding strategies than C. sapidus and C. bocourti. Substrate type can also influence predation, as was found for Callinectes sapidus where predation on clams was lower in sand than mud (Lipcius and Hines, 1986). Our results suggest an ontogenetic trend of increasing predatory behavior with increasing size; a trend found for C. sapidus in Florida (Laughlin, 1982) and some Pacific Callinectes spp. (Paul, 1981). Laguna Joyuda has a lower number of large prey species (Stoner and Acevedo, in press); therefore, larger crabs might be expected to consume the same major prey items, with variation in proportions. The largest crabs consumed more fish, shrimp, crabs, and molluscs in varying proportions among species. Smaller crabs consumed a wider variety of prey which were often small and probably not energetically useful as prey for larger crabs (e.g., amphipods, foraminiferans, and polychaetes; especially in 2l-30-mm CW crabs). Strong differences in prey among crab species in the smallest size classes may indicate behavioral or morphological differences in feeding among species. Strong differences among size classes suggest size-related changes in feeding apparatus, especially the size of feeding appendages. Determination of crustacean diets on the basis of gut contents is associated with a number of well recognized limitations such as different digestion rates for various prey organisms and variation with season, site, sex, and gut fullness (Elner and Campbell, 1987). Because numbers of crabs in our collection were not high and because of our primary interest, the role of Callinectes spp. as predators in the STONER AND BUCHANAN: CALLINECTES SPP. DIETS 11 lagoon system, we have not extracted all of the potential sources of variation in diets, such as the switch in diets from fish to shrimp associated with changing prey abundance. Examination of stable carbon isotope ratios on Callinectes spp. and other components of the Laguna Joyuda system (Stoner and Zimmerman, 1988), however, provides good evidence that the animals in the guts are the actual sources of carbon for the crabs. Capitellid polychaetes, amphipods, penaeid shrimp, Macoma brevifrons, hermit crabs, C. sapidus, and C. danae all had relatively high A13C values (-15.4 to -18.8). Barnacles, other crab species, and copepods all had highly negative values (- 23.0 to -25.9). Carbon isotope ratios do not permit determination of the relative importance of the prey organisms, but Stoner and Zimmerman (1988) showed that the food web leading to penaeid shrimps and Callinectes spp. is not detritus-based as has been generally believed. Rather, th(: blue-green algal mat which is very abundant on mangrove roots in the lagoon and which covers much of the lagoon sediment (Rodriguez and Stoner, in press) is the primary source of carbon to decapod consumers. Data on sympatric Callinectes spp. from Laguna Joyuda show that portunidl crabs are not readily accommodated in trophic levels or in concepts of feeding guilds, and lends support to the suggestion of incorporating age-specific trophic progressions in the analysis of systems functions (Livingston, 1980; 1982; 1984; Stoner, 1980; Leber, 1983; Stoner and Livingston, 1984). Livingston (1982; 1984) has been particularly successful using "ontogenetic trophic units": in the explanation of long-term, seasonal, and spatial relationships between fish community structure and habitat characteristics. Similar strategy might be applied equally well to decapod crustaceans, and a careful description of trophic interactions constitutes an important first step in understanding any ecological system. ACKNOWLEDGMENTS This research was supported by the Office of Sea Grant, NOAA (Grant No. RJA-01-2) and a grant from the National Science Foundation (No. R-II-86 10677). D. Corales participated in all ofthe field work, and L. L. Cruz conducted the gut analyses. The manuscript was reviewed by Dr. K. M. Leber, C. Perry and J. van Montfrans. LITERATURE CITED Blundon, J. A. and V. S. Kennedy. 1982. Mechanical and behavioral aspects of blue crab, Callinectes sapidus (Rathbun), predation on Chesapeake Bay bivalves. 1. Exp. Mar. BioL EcoL 65: 47-65. Bray, 1. R. and J. T. Curtis. 1957. An ordination of the upland forest communities of southern Wisconsin. EcoL Monogr. 27: 335-349. Buchanan, B. A. and A. W. Stoner. 1988. Distributional patterns of blue crabs (Callinectes spp.) in a tropical estuary. Estuaries II: 231-239. Carr, W. E. S. and C. A. Adams. 1972. Food habits of juvenile marine fishes: evidence of cleaning habit in the leatherjacket, Oligoplites saurus, and the spottail, Dip/odus ho/brooki. Fish. Bull., U.S. 70: 1111-1120. Darnell, R. M. 1958. Food habits of fishes and larger invertebrates of Lake Ponchartrain, Louisiana, an estuarine community. Publ. 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