Bathymetric patterns of body size in deep-sea gastropods

The shift to smaller body size in marine invertebrates at the deep-sea thre shold and size-depth dines within the deep-sea ecosystem are global biogeog raphic phenomena that remain poorly understood. We present the first standa rdized measurements of larval and adult size among ecologically and phyloge netically similar species across a broad and continuous depth range, using the largest family of deep-sea gastropods (the Turridae). Size at all life stages increases significantly with depth from the upper bathyal region to the abyssal plain. These consistent dines may result from selection favorin g larger size at greater depths because of its metabolic and competitive ad vantages. The unusually small size of deep-sea mollusks, in general, may re present an independent evolutionary process that favors invasion by inshore taxa composed of small organisms.