Seasonal diet and feeding habits of juvenile fishes foraging along a subtropical marine ecotone

Few studies have examined seasonal diet variation and trophic relationships among fishes in shallow subtropical waters. We sampled consecutive wet and dry seasons within Biscayne Bay, Florida, USA, to examine seasonal diet and feeding habit variation in juvenile gray snapper Lutjanus griseus (GS), bluestriped grunt Haemulon sciurus (BSG), seabream Archosargus rhomboidalis (SB) and great barracuda Sphyraena barracuda (GB). We found significantly lower feeding intensity during the dry season compared to the wet, which is likely related to lower water temperatures during the former season. GS fed on a variety of fishes and crustaceans, while BSG fed primarily on caridean shrimps. SB fed on vegetation and GB was piscivorous. Seasonal shifts in major food resources generally did not correspond with changes in relative abundance of food supply. Seasonal population niche breadth differences were evident for GS, GB and BSG, but for SB niche breadth was similar between seasons. Based on seasonal food supply, population niche breadth values did not match basic foraging theory predictions, which state that niche breadth should expand as preferred food items become scarce. In GS, BSG and GB, individuals fed on a narrow subset of prey consumed by the population, revealing the existence of individual specialization. For these species, seasonal expansion in population niche breadth did not correspond to increased individual specialization, but rather via increased within-individual variation in resource use. Given the seasonal differences in feeding habits, it is important to incorporate seasonal variation when modeling trophodynamics of shallow subtropical systems or characterizing them as essential fish habitats.