Are Caribbean mangroves important feeding grounds for juvenile reef fish from adjacent seagrass beds?

Little evidence is available on how juvenile fishes utilise seagrass beds and adjacent mangroves as feeding habitats. In this study we tested the degree to which Caribbean mangroves are utilised as feeding grounds by the fish community from adjacent seagrass beds. Stable carbon and nitrogen isotope analyses were performed on several potential food items from seagrass beds and adjacent mangroves, on muscle tissue of 23 fish species from seagrass beds on a Caribbean island (Curacao, Netherlands Antilles), and on juveniles of 2 common reef fish species, Haemulon flavolineatum and Ocyurus chrysurus, from seagrass beds in 7 bays on 5 Caribbean islands. Only the herbivore Acanthurus chirurgus and the carnivore Haemulon chrysargyreum appeared to feed predominantly in the mangrove habitat, whereas the carnivores Mulloidichthys martinicus and O. chrysurus (only on 2 islands) showed a stable carbon signature suggestive of food intake from the mangrove as well as the seagrass habitat. The piscivore Sphyraena barracuda foraged on fish schooling at the mangrove/seagrass interface. For the other 18 seagrass fish species, which contributed 86 % of the total seagrass fish density, the contribution of food sources from the mangroves was minor to negligible. The same was true for H, flavolineatum and 0, chrysurus on most of the other Caribbean islands. The results contrast with the situation in the Indo-Pacific, where intertidal mangroves serve as important feeding habitats for fishes from adjacent systems during high tide. This difference is most probably explained by both the absence of large tidal differences on Caribbean islands and the greater food abundance in seagrass beds than in mangroves.