Community structure of reef fish in several habitats of a rocky reef in the Gulf of California

To explore the relationships between habitat structure, distribution, and diversity of conspicuous reef fish, surveys were made in 1994, 1995 and 1998 at Los Islotes, a rocky islet located north of Bahia de La Paz, B.C.S., Mexico. The site was divided into six zones, which presented different habitats: rhodoliths, walls, big boulders, small boulders and black coral. Some physical descriptors for the substrate were determined: depth, rugosity, number and size of rocks, and the percent coverage of several types of sessile invertebrates. Number of species and abundances were determined by visual transects. Two main seasons were distinguished, and the number of species was different between seasons and among zones. Four fish groups were identified based on the frequency and abundance of species. These fish groups presented similar proportions in each zone. Although most species recorded at Los Islotes were to were found in all the studied habitats, their densities varied significantly between habitats, suggesting groups of 'representative' species. Correlation analysis showed relationships between physical characteristics and the 'representative' species, that can be explained by the natural history of each species, including feeding behavior and shelter requirements.