Mollusk death assemblages from the deep slope off northwestern Cuba (Gulf of Mexico)

We evaluated the mollusk death assemblages along seven sites in a deepsea expedition off northwestern (NW) Cuba. We aimed to (1) provide the first baseline of mollusk diversity in sediments of the NW region, and (2) test if there were west-east gradients of α- and β-diversities. We found 141 species in sediments: 68 deepsea benthic, 43 shelf benthic, and 30 pelagic species. The richness of pelagic species was similar along the NW region indicating significant settlement of pteropod shells to the seabed. The occurrence of shelf species in the deepsea suggested a downslope transport of shells enhanced by the slope steepness and dredging in two ports. β-diversity of deepsea benthic mollusks showed a high turnover at local scales explained by habitat heterogeneity. β-diversity of pelagic species was extremely low suggesting that the planktonic assemblage was evenly distributed. In contrast, high β-diversity of shelf benthic species occurred likely due to downslope transportation of materials. Deepsea gastropods were mostly detritivores, while bivalves were mostly suspension feeders. These dominant biological traits indicated oligotrophic conditions in sediments likely coupled with an intense hydrodynamic regime in the deepsea. The NW Cuban region seems to be a hotspot for mollusk diversity because of the discovery in a single expedition of seven new species, 12 new records, and 36% endemism relative to the entire Gulf of Mexico. Our findings revealed a complex and diverse mix of deep/pelagic/shelf species but did not indicate a west-east gradient in the mollusk assemblage structure.