Feeding Ecology of the Schoolmaster Snapper, Lutjanus Apodus (walbaum), from Southwestern Puerto Rico

Stomach contents from 449 schoolmaster snapper, Lutjanus apodus, from southwestern Puerto Rico were examined. Hierarchical cluster analysis identified two primary trophic groups: ::;70 mm FL and >70 mm FL. Small L. apodus (::;70 mm) fed almost exclusive]y on crustaceans (89% by weight; 95% by numbcr; 98% frequency of occurrence), particularly amphipods and crabs, By contrast, L. apodus greater than 70 mm preferred piscine prey (57% by weight; 37% by number; 63% frequency of occurrence) and supplemented their diets with crabs, shrimp, and stomatopods, Ontogenetic patterns in diet were related to changes in jaw morphology (i.e., gape dimensions). Moreover, spatial and temporal variations were sizerelated and appeared to play some role in structuring the diet of L. apodus. Small L. apodus (::;70 mm) were found only in mangrove prop-root habitats and showed peak fecding at midday, Larger L. apodus (>70 mm) were present in both mangrove and coral reef habitats and showed ]ittle variation in diurnal feeding periodicity. Prey selection patterns of L. apodus were influenced by habitat and season. The schoolmaster snapper, Lutjanus apodus (Lutjanidae), is the most commonly encountered lutjanid on coral reefs in the Caribbean (Randall, 1983) and Bahamas (Bohlke and Chaplin, 1968). L. apodus appears confined to reefs more than other snappers (Randall, 1967); however, it has also been reported as the predominant lutjanid in areas adjacent to or inside mangrove prop-root habitats (Austin, 1971; Austin and Austin, 1971; Kimmel, 1985; Rooker and Dennis, 1991). L. apodus is a highly esteemed food fish and an integral part of the commercial and sport fisheries in the West Indies and other areas of its geographic range which extends from northern Brazil to Massachusetts (Allen, 1985). Although L. apodus plays an important trophic role in tropical marine communities, little is known regarding its feeding ecology in such ecosystems. Investigations of the food habits of L. apodus are limited to large-scale ichthyofaunal studies in which diet information is presented in qualitative terms and drawn from small sample sizes (Beebe and Tee-Van, 1928; Longley and Hi ldebrand, 1941; Randall, 1967; Austin and Austin, 1971; Starck, 1971). Detailed quantitative assessment of the food habits of L. apodus, including the effect of ontogeny, is lacking. The objectives of this study were to describe the diet of L. apodus quantitatively, determine ontogenetic patterns in diet, and determine the relevance of diel feeding periodicity, habitat, and season to these patterns. MATERIALS AND METHODS Study Area.-Mangrove and coral reef habitats located off La Parguera, Puerto Rico were selected as sampling sites for this study (Fig. ]). Habitat determination was based on random selection of sites from each of five habitat types. Mangrove collections were limited to two types: shoreline mangroves and mangrove keys. Mangrove sites were dominated by the red mangrove (Rhizophora mangle) and characterized by shallow « 1.0 m) water. Three different coral reef habitats were distinguished and sampled: a) Inshore, shallow water (Ahogado, Collado), b) Inshore, moderate depth (Enrique, Margarita, Media Luna), and c) Offshore, moderate (Turrumote) to shelf edge depth. Inshore shallow water reefs were characterized by large stands of elkhorn coral (Acropora pa/mata) ncar the surface, with fire coral (Millepora alcicornis) dominant at the base of the reef (ca. 4 m), Inshore, moderate depth reefs ranged in depth from 5 to 10 m. Coral composition was similar to shallow water reefs with the