Rocky-reef fish assemblages at San Jose Island, Mexico

The composition, diversity, and abundance of marine fish at rocky reefs off San Jose island, Mexico between October 2001 and August 2002 were studied. Fish species were recorded using a visual census in 5 sampling areas of 50 by 5 meters at 2 depths, shallow (1-3 meters) and intermediate (5-7 meters). A total of 26946 organisms were counted, belonging to 84 species. The families Serranidae (9 species), Labridae (8), Pomacentridae (7), and Haemulidae (6) were the most representative. The rugosity of the bottom surface, showed a positive relationship with abundance, richness, and fish diversity. The ocean bottom off San Jose island is covered with various size rocks that offer more feeding and refuge areas to fish assemblages than other areas. The ecological index increased during the warm season. Diversity and richness showed significant variations by depth, with the highest values in exposed locations around the island. The biological value index indicated that the most representative fish species were Stegastes rectifraenum, Abudefduf troschelii, Thalassoma lucasanum, Scarus ghobban, and Mulloidichthys dentatus. The depth and wave exposure were the 2 environmental variables which most influenced the structure of rocky-reef fish assemblages.