Habitat associations and aggregation of recruit fishes on Hawaiian coral reefs

Associations with structural habitat complexity and the aggregation of individuals lessen the risk of predation, and both are commonly observed for recently settled fishes on coral reefs. On reefs fringing Hawaii Island, such recruits of many fishes, particularly two species of surgeonfishes, exhibited strong affinities for branching finger coral (Porites compressa Dana, 1846), the most structurally complex coral available in the relatively low-diversity assemblage of Hawaiian reef corals. Recruits of these species also aggregated with conspecific and heterospecific recruits as they associated with this coral. That recruits of reef fishes take refuge in the best available shelter, however, is not a novel observation. More noteworthy is the frequent co-occurrence of recruits with other recruits of the same and other species. Our observations suggest that small juvenile reef fishes aggregate near preferred coral habitat and perhaps also with one another independently of habitat per se, the latter a phenomenon that has been generally overlooked by researchers focusing on evidence for density-dependent negative interactions within juvenile reef fishes. Because interactions between habitat structure and aggregative behaviors have the potential to importantly modify the survivorship of recruits that may influence year-class strength, they merit further study.