Resumen del producto

We analyze the composition and community structure of soft-bottom molluscs of Isla SanFrancisco (24°48' N, 110° 34' W) and its possible relation to sorne environmental variables. Weselected 18 sampling si tes on the summer of 2012. 36 samples were collected, 18 correspond tobiological samples and 18 to sediment. The temperature, depth, sediment type, and organkmatter were used as ambient indicators. We analyzed the abundance and diversity of themalacological benthic community as ecological dcscriptors. 2773 specimens were registeredbelonging to 35 species of bivalve distributed in 12 familics and 5 orders. The gastropods werethe most represented group with 44 species distributed in 25 families and 6 orders. The highestvalues of richness and abundance were found south of the island in carbonate sediments ofcoarse sand and shallow bottoms. The most abundant bivalves were Tellina eburnea with anaverage sizc of 5 mm followed in importance by Gari helenae, the most abundant gastropod wasthe micromollusc Cystiscus politulus. The species with the highest frequency of occurrence (2:50%) were: Laevicardium substriatum (58%), Crepidula aculeata (58%); Gari helenae (50%)and Lucina undatoides (50%). The mean values of diversity index was 2.7 bits 1 ind., and theevcnncss was high (> 0.8) in most of the sample sites. The mínimum value recorded was 0.65influenced by the abundance of the bivalve Tellina eburnea that was the dominant species. Wefound a strong association of molluscs with deposits of calcateous algae, pieces of coral andechinodenns.

Palabras clave: soft bottom molluscs; Gulf of California

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