Reef fish community structure in Bocas del Toro (Caribbean, Panama): Gradients in habitat complexity and exposure

We compared the community-structure of reef-fish over different spatial scales, levels of exposure, and physical complexity in 12 study zones of Bocas del Toro, Panama. Two hundred and eighty-eight visual censuses were conducted on 48 benthic transects from April to September 2002. Substrate coverage and surface complexity was also recorded. We found 128 fish species in 38 families with increasing species richness from sheltered to expose and from low-complexity to intermediate and high-complexity zones. Only 7% of the species occurred in all zones. Gobies and pomacentrids were most abundant in sheltered areas and labrids at exposed zones. Eleven species showed significant size-segregations between zones, suggesting ontogenic movements, with smaller sizes in low-complexity zones, and larger-sizes in intermediate to high complexity areas. Species-richness and diversity are high in three of the four exposed zones and in the main areas of massive-coral reefs and significantly correlate with certain types of complex substrates. Highly mobile fish were more abundant in exposed rocky zones while sedentary fish were more abundant in sheltered massive and foliaceous corals zones. Towards the most exposed areas, the number of mobile invertebrate-feeding fish species greatly increased, while territorial herbivores increased in sheltered zones. Roving herbivores (scarids and acanthurids) showed lower frequency than territorial herbivores in all zones. Demersal zooplankton feeders were common in sheltered areas and oceanic planktivores in exposed areas. Omnivores were more abundant in zones of rubble and sand. Carnivores were less frequent, but contribute to the majority of species. We concluded that the species' richness in Bocas del Toro relates to the structural complexity of the substrate rather than substrate type. While some species change their preferred habitat during ontogeny, general species diversity increased with habitat complexity. This increase was more pronounced in exposed zones. It seem that water current strength and waves, which select for swimming capacity, play an important but still little understood role in the organization of fish assemblages in rocky and coral reefs.