Ontogenetic patterns in resource use dynamics of bonefish ( Albula vulpes ) in the Bahamas

We used stable isotope analysis to examine ontogenetic patterns in the resource use dynamics of bonefish (Albula vulpes) collected from two locations (Banks and Atlantic) within the coastal waters of Eleuthera, The Bahamas. A marked shift in δ13C signatures between leptocephali and juveniles reflected a rapid change in resource use, likely from pelagic to alternate neritic sources of primary production. Ontogenetic shifts in habitat use were observed across bonefish from both sides of Eleuthera, but direction of the isotopic shifts varied. Bonefish from the Atlantic side demonstrated an enrichment in 13C with size, whereas the opposite pattern was observed for individuals captured from the Banks. Differences are likely to be explained by the variability of primary production sources, which dominate each side of the island (i.e., more reliance on seagrass with ontogeny on the Atlantic side, versus a shift to macroalgal-dominated foodwebs with growth on the Banks side). Enrichment in 15N with body size was observed for both locations and reflects the ability to utilize a broader range of prey items with increasing gape size. Trophic diversity (inferred through nitrogen range), however, was lower on the Banks side, suggesting that reduced prey diversity may limit the increase in dietary shifts that gape size increases typically allow. A significant positive relationship between δ13C and whole-body energy density (MJ kg-1) in adults on the Banks side was observed. Adult bonefish that forage in seagrasses likely benefit from higher energy densities from selected prey items, and may explain this result. Data from this study reinforces the importance of a diversity of habitats in supporting bonefish throughout ontogeny.