Refuge availability structures assemblages of tropical reef fishes

1. We examined assemblage structure of tropical fishes on small, artificial reefs to determine if differences in refuge availability could modify patterns of species richness and abundance of fishes established at recruitment. 2. Our artificial reefs were designed to provide prey refuge of two types (permanent and transient), Permanent refugia are those that physically exclude predators, i.e. small holes provide permanent refuge from large-bodied predators. Transient refugia result when habitat complexity increases the probability that prey will elude predators. These refugia do not physically exclude predators and thus provide no permanently safe sites. 3. We conducted this experiment at two widely separated locations on Australia's Great Barrier Reef. The species pools of reef fishes, recruitment rates and predator densities all differ between these locations. 4. At neither location were patterns of recruitment influenced by the presence of either type of refuge. By the end of the experiment, however, there were more resident fishes on reefs with additional refugia. 5. Species richness of residents was positively related to total abundance of residents. Therefore, refuge availability indirectly affected species richness through its effect on abundance. There was no indication, however, that permanent refugia provided any greater protection to prey species than did transient refugia. 6. Our results therefore indicate that for these communities, patterns of species richness and abundance established at settlement can be modified considerably over small spatial and temporal scales by differences in refuge availability. Furthermore, habitat complexity need not provide permanently safe sites to affect patterns of coexistence.