Biogeographic and bathymetric patterns of benthic molluscs in the Gulf of Mexico

Abstract

The Biodiversity of the Gulf of Mexico (BioGoMx) database, which contains occurrence information of extant species in the Gulf of Mexico (GOM), allows for the analysis of benthic mollusc diversity and distribution across the entire basin. For analyses, the GOM was split in 4 geographic sectors (NE, NW, SE, and SW) and 6 depth classes (inshore, upper shelf, lower shelf, upper slope, lower slope, and abyssal plain) for a total of 24 geographic-depth polygons. The northern GOM contained higher species richness than the south, the east more than the west. Species richness decreased with depth with maxima occurring on the upper shelf. Bivalves and gastropods dominated each geographic sector and depth class, together comprising >90% of the molluscan species richness. Assemblages were structured by depth more than by geographic sector. GOM molluscs fell into 3 broad depth-based assemblages: the inshore and continental shelf, the continental slope, and the abyssal plain species combined with the western lower slope. Geographically, taxonomic distinctness analysis indicated most NE depths fell below average distinctness and by depth polygons above and below the continental shelf break were frequently distinct. Cluster analysis based on taxonomic dissimilarity agreed with the analyses based on the species occurrence data. Mollusc feeding strategies largely followed estimated proportions for the larger Atlantic. Carnivory and suspension feeding were the most common with grazing, herbivory, and parasitism following behind. Chemosymbiotic species were also prevalent due to the widespread occurrence of cold seep habitats. Further taxonomic research and more sampling are needed to determine patterns at finer scales.