Abstract

Mangroves are considered as important source of organic matter for adjacent marine ecosystems due to their high primary production. Yet, there is still a debate on the contributions of mangrove carbon to foodwebs due to the influence of adjacent habitats, such as seagrass beds. To determine the importance of these two ecosystems as fish feeding grounds, stable carbon isotopes (13C:12C) and nitrogen isotopes (15N:14N) ratio techniques were performed on seven fish species of commercial interest and their potential food items in mangrove shoreline sites and adjacent seagrass beds in Guadeloupe. The IsoSource mixing model was used to determine the range of contributions of several potential food items in the consumers diet. On the basis of their δ13C, prey items collected in mangroves were more depleted in 13C (δ13Cmean = -20.7 ± 1.2‰) than those from seagrass beds (δ13Cmean = -13.0 ± 4.7‰). The δ13C signatures of most reef fishes from fringing mangroves were similar to those of prey items from seagrass beds, suggesting that these fish feed from seagrass habitats. Only two species, the second order carnivore Ocyurus chrysurus and the piscivore Tylosurus crocodilus, appeared to feed to a larger extent in mangrove habitat. Moreover, ontogenetic resource partitioning was observed for the carnivorous species O. chrysurus, with small juveniles feeding on zooplankton and invertebrates from mangrove habitat and larger specimens consuming invertebrates and fishes from seagrass beds. These findings show that seagrass beds represent important feeding grounds for juvenile reef fish species of commercial interest during their mangrove habitat phase.

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