Estructura de la Comunidad de Moluscos de Fondos Blandos de la isla San Francisco, golfo de Cafornia, México

We analyze the composition and community structure of soft-bottom molluscs of Isla San Francisco (24°48' N, 110° 34' W) and its possible relation to some environmental variables. We selected 18 sampling sites on the summer of 2012. 36 samples were collected, 18 correspond to biological samples and 18 to sediment. The temperature, depth, sediment type, and organic matter were used as ambient indicators. We analyzed the abundance and diversity of the malacological benthic community as ecological descriptors. 2773 specimens were registered belonging to 35 species of bivalve distributed in 12 families and 5 orders. The gastropods were the most represented group with 44 species distributed in 25 families and 6 orders. The highest values of richness and abundance were found at south of the island in carbonate sediments of coarse sand and shallow bottoms. The most abundant bivalves were Tellina eburnea with an average size of 5 mm high followed in importance by Gary helenae, the most abundant gastropod was the micromollusc Cystiscus politulus. The species with the highest frequency of occurrence (≥ 50%) were: Laevicardium substriatum (58%), Crepidula aculeata (58%); Gari helenae (50%) and Lucinaun datoides (50%). The mean values of diversity index was 2.7 bits / ind., and the evenness were high (> 0.8) in most of the sample sites, the minimum value recorded was 0.65 influenced by the abundance of the bivalve Tellina ebúrnea that was the dominant species. We found a strong association of molluscs with deposits of calcareous algae, pieces of coral and echinoderms.