Transition from pelagic to demersal phase in early-juvenile Nassau grouper, Epinephelus striatus Pigmentation, squamation, and ontogeny of diet

Early-juvenile Nassau grouper, Epinephelus striatus, were collected offshore, in tidal passes, and in shallow bank habitats in the southern Exuma Cays, Bahamas, during winter in 1993 and 1994, encompassing a complete transition from pelagic to demersal phase. Collected fish were examined in terms of pigmentation, squamation, and ontogeny of diet during settlement. While pelagic, during January and February, early juveniles were uniform in their pigmentation, but varied considerably in scale development. Once settled into macroalgal bank habitats, during February, demersal early juveniles were uniform in scale development, but varied in pigmentation. Complete settlement pigmentation and scale development were first observed in February and March, respectively. The diet of pelagic juveniles was dominated by calanoid and poecilostomatoid copepods, and decapod larvae. The diet of demersal post-settlement juveniles was dominated by gammaridean amphipods and harpacticoid copepods. Six months later, shortly before E. striatus are thought to vacate macroalgal habitats, early juveniles were collected, to examine ontogenetic shifts in diet during their tenure in macroalgae. Although gammarideans continued to dominate the diet at that time, isopods and mysids increased in importance. In settlement habitats, feeding success may be related to the development of settlement coloration. Ecological adaptation to settlement habitats appears to be relatively rapid: the transition from pelagic to demersal phase appears to be completed within 1 wk.