Mollusk distribution in four habitats along a salinity gradient in a coastal lagoon from the Gulf of Mexico

Molluscs are an important component of the macrofauna at coastal lagoons and a relevant invertebrate group used as an ecological indicator of environmental impacts on these ecosystems. In this study, we used a multivariate approach to assess spatial distribution changes of molluscan assemblages along a salinity gradient in four habitats from a tropical coastal lagoon. Throughout 1 year, we collected samples at six sites in four identified habitats: i) muddy bottom near a fringing mangrove (MAN), ii) mangrove (Avicennia germinans) roots (RAI), iii) sandy-muddy bottom (ARE) and iv) submerged aquatic vegetation (VAS). We identified 29 molluscs species. The gastropodsNeritina virgineaandN. reclivatawere the dominant species in the lagoon and bivalvesRangia flexuosa, Ischadium recurvum, andCrassostrea virginicaoccurred in all habitats and sites. Greater species richness was found during the rainy season and in the VAS habitat. Molluscan assemblages varied among seasons, habitats, and sites nested within habitats. Environmental variables that best explained seasonal molluscan assemblages were temperature and turbidity; along the lagoon, the best variables that explained molluscan assemblages were salinity and dissolved oxygen. This study supports the argument that preventing habitat loss or habitat conversion is an important issue to be considered for molluscan conservation at estuarine ecosystems.