Post-settlement transition in coral reef fishes: overlooked complexity in niche shifts

Events that occur during the transition between phases in a complex life history can have major consequences for the demography of populations. Life-history theory suggests that transitions should be abrupt to maximize survival in each life stage. We compare the transition from dispersive larva to settled juvenile in 3 common coral reef fishes, which were chosen to span a wide range of trophic groups, morphological forms and adult ecologies: a benthic microcarnivore, the goatfish Parupeneus multifasciatus (family: Mullidaei; a planktivore, the dartfish Pteroleotris evides (Microdesmidae); and a largely herbivorous damselfish, Pomacentrus amboinensis (Pomacentridae). Transitions from settled post-larva to juvenile varied in complexity and ranged from immediate to a gradual process lasting 3 wk. The goatfish displayed 3 distinct shifts in habitat and associations with other species within 2 wk of settlement before joining the juvenile population, while the dartfish displayed 2 major shifts in a 3 wk period. These habitat shifts coincided with changes in morphology associated with metamorphosis. In contrast, the damselfish settled directly into its adult habitat, and displayed neither shifts in habitat or species association nor a dramatic metamorphosis. Evidence suggests that the magnitude and duration of ecological shifts during the settlement transition can be predicted from information on the extent of metamorphosis.