Mollusc species richness and abundance from shelf to abyssal depths in the Ross Sea (Antarctica): the importance of fine-mesh-towed gears and implications for future sampling

In polar areas, where benthic sampling is constrained by a series of limitations imposed by climate and logistic challenges, knowledge about the key elements required to plan a successful survey is fundamental. During the International Polar Year (IPY, 2007/2008), under the Census of Antarctic Marine Life (CAML), new sampling campaigns were undertaken in several Antarctic areas comprising the Ross Sea. In this region, the 2008 NIWA IPY-CAML voyage obtained benthos samples from shelf to abyssal depths. In the present study, we focus on the Mollusca from this expedition and on the possible variations in their richness and composition with latitude and depth. Given the use of sampling gears selective for different size fractions of the macrofauna, we also assess which size fraction contained the highest biodiversity. Differences were detected in species composition with latitude (averaged across depth groups) but not for depth (averaged across latitudinal groups). Richness varied locally and showed a variety of patterns depending on the areas and depths considered. The greatest diversity of molluscs was found in the fine fraction (i.e.,