Food Habits of Juvenile Marine Fishes Occupying Seagrass Beds in the Estuarine Zone near Crystal River, Florida

Abstract

Quantitative gravimetric analyses of stomach contents were carried out on juveniles of 21 species of fishes that cohabit seagrass beds near Crystal River, Florida. Our analyses were based on dry weights of food items and are expressed as percent of total stomach contents. The species analyzed were Harengula pensacolae, Opisthonema oglinum, Anchoa hepsetus, Anchoa mitchilli, Synodus foetens, Strongylura marina, Hyporhamphus unifasciatus, Oligoplites saurus, Trachinotus falcatus, Eucinostomus gula, Haemulon plumieri, Orthopristis chrysoptera, Bairdiella chrysura, Cynoscion nebulosus, Diplodus holbrooki, Lagodon rhomboides, Microgobius gulosus, Chasmodes saburrae, Menidia beryllina, Trinectes maculatus, and Sphoeroides nephelus. Analyses of stomach contents taken from small, sequentially arranged size classes enabled us to delineate discrete ontogenetic changes in food habits in many of the species. In the 15 species in which planktivorous feeding stages were detected, only zooplankters were consumed in measurable amounts. Juveniles of H. pensacolae, O. oglinum, A. hepsetus, A. mitchilli, and M. beryllina were almost exclusively planktivorous throughout most of the available size ranges and exhibited a distinct selection for molluscan veliger larvae. Copepods, mysids, and larval crustaceans were the principal plankters consumed by juveniles of other species. Only three species, D. holbrooki, L. rhomboides, and H. unifasciatus, exhibited herbivorous feeding stages. In both D. holbrooki and L. rhomboides, the herbivorous habit began quite early in juvenile development and followed a preliminary planktivorous stage. Larger specimens of L. rhomboides became carnivorous, whereas adults of D. holbrooki (and H. unifasciatus) were herbivorous. Juveniles of eight species exhibited carnivorous feeding stages, consuming primarily benthic invertebrates. Of these species, O. saurus, H. plumieri, O. chrysoptera, and B. chrysura consumed primarily shrimp and mysids; E. gula and T. maculatus utilized primarily polychaetes; C. saburrae consumed primarily amphipods; and T. falcatus consumed mainly crabs after utilizing mysids, small shrimp, and fishes in earlier feeding stages. In O. saurus, an intermediate stage was apparent in which material obtained from a cleaning habit made an important contribution to the diet. Juveniles of two species, L. rhomboides and C. nebulosus, exhibited carnivorous stages in which both benthic invertebrates and small fishes were important in the diet. Specimens of S. marina and S. foetens were primarily piscivorous. Detritus was an important dietary component in six species. In S. nephelus, M. gulosus, and C. saburrae, detritus was a major food item throughout most of the available size ranges. In M. beryllina, detritus was the major food item in the smallest size class examined. Appreciable amounts of detritus were also consumed by juveniles of O. oglinum and adults of H. unifasciatus.