Factors affecting resource use variation for an abundant coastal fish predator, Lutjanus apodus, in a bahamian wetland system

Abstract

Studies of fishes' resource use reflect important ecological interactions, and provide insight into the structure of aquatic food webs. Individuals within species are often assumed to have an equivalent ecological role despite increasing evidence that among-individual variation in resource use within populations is common. Such intraspecific variation in resource use can be a result of ontogenetic-based diet shifts, differences in individual feeding behavior within age groups (i.e., individual specialization), and temporal variation in resource pools. We examined trophic interactions in schoolmaster, Lutjanus apodus (Walbaum, 1972), over multiple seasons and across size classes in a Bahamian wetland system. Using combined stable isotope and stomach content analyses, we found that, as with many other fishes, subadults fed at higher trophic levels than juveniles, likely because of a shift from feeding predominantly on lower trophic-level prey taxa (e.g., crabs) to higher trophic-level prey taxa (e.g., teleosts). Despite a considerable overlap in stable isotope values between subadults and juveniles, stable isotope and stomach content data suggest a switch from feeding predominantly within mangrove prop roots as juveniles to foraging increasingly in adjacent seagrass beds as subadults. Niche width and degree of individual dietary specialization varied among years, suggesting important levels of temporal variation. In sum, individual snapper do not use resources homogeneously, and we outline some of the factors, including predation risk, increase piscivory, and temporal differences in resource use, that underlie this variation.