Habitat type and schooling interactively determine refuge-seeking behavior in a coral reef fish throughout ontogeny

Habitat selection by coral reef fish is influenced by a variety of biological and abiotic factors, but the relative importance of these factors is expected to change throughout ontogeny, especially for species that utilize different habitats during their life cycle. In this study, 2 in situ choice experiments were designed to test the individual as well as the interactive effects of habitat structure and schooling (with conspecifics or heterospecifics) on refuge-seeking behavior of a coral reef fish. The experiments were conducted for 3 size-classes of the common reef fish Haemulon flavolineatum, a species that shows multiple habitat shifts throughout its ontogeny. We tested the hypothesis that, due to the additive effects of schooling and structure in providing suitable refuge, fish would be more attracted to a microhabitat with conspecifics or heterospecifics than to a microhabitat or conspecifics alone. In the habitat-only experiment, early juveniles (less than 3 cm fork length) showed no preference for any microhabitat structures, whereas larger fish preferred complex mangrove structure to seagrass, rubble, or coral. In the second experiment, which offered various combinations of habitat, including habitat with both conspecifics and heterospecifics, the preference for mangrove structure was completely replaced by attraction to conspecifics for all size-classes. Unexpectedly, the combination of conspecifics and habitat structure showed no additive effect. The results demonstrate that although H. flavolineatum makes multiple shifts in habitat throughout its life cycle, in the absence of other biological or environmental drivers preference for shelter habitat past the early post-settlement stage remains the same. The study further demonstrates the critical role of the presence of conspecifics in microhabitat choice, and provides a better understanding of the relative importance of these factors, whether in isolation or additively, in selection of refuge habitat by a reef fish