Corals on seamount peaks provide evidence of current acceleration over deep-sea topography

Abstract

Geological and physical studies of seamounts have suggested the existence of distinct deep-sea habitats, characterized by exposed rocky bottom and a unique current regime^1–9. However, few biological data have been collected for deep seamounts^10–12. Here we present some of the first quantitative observations of hard-bottom (non-hydrothermal) fauna in the deep sea. These observations show that black corals (antipatharians) and horny corals (gorgonians) present on the slopes of a multi-peaked seamount are more abundant near peaks, compared with mid-slope sites at corresponding depths. On narrow peaks corals are most abundant on the crest, whereas on wide peaks, coral densities are highest at the edge of the crest. The abundance of corals also increases on knobs and pinnacles. Physical models and observations^{2,4–9,13–15}, together with our direct measurements, suggest that the seamount topography affects the local current regime. Corals appear to benefit from flow acceleration, and some of their patterns of distribution can be explained by current conditions. These results suggest that suspension feeders have some potential as indicators of prevailing currents at deep hard-bottom sites.