Bathymetry and body size in marine gastropods: a shallow water perspective

Spatial patterns of species body size across major environmental gradients are being quantified for terrestrial organisms, but similar efforts are largely lacking for marine invertebrates. Bathymetry represents a major environmental gradient in the oceans, and existing theoretical models predict that species body size should decrease with increasing depth, especially for deep-sea species. Previous analyses of body size in deep-sea gastropods have shown size to increase with depth and hence contradict model predictions. In this study, I use data for 636 species of gastropods (in 10 major groups) living on the NE Pacific continental shelf to test hypotheses about processes that determine size-depth trends in marine gastropods. Results show that the gastropod family Turridae, a major component of both shallow-water and deep-sea biotas, shows similar size-depth trends in both environments but that predominantly shallow water families may show different patterns. In addition, size-depth trends may differ between clades and between different trophic groups. The implications of these results for better understanding the processes that underlie bathymetric trends in body size are discussed.