DEEPWATER HARD SUBSTRATE COMMUNITIES ON SEAMOUNTS IN THE WESTERN NORTH ATLANTIC

Most deep-sea habitats are covered by accumulations of sediment. Hard substrates are therefore spatially limited in the deep sea and found under special conditions. Examples of hard substrates in the deep sea can be found in areas of volcanic activity and/or strong currents. For the past few years our group has been researching the New England Seamounts, which extend southeast from the continental slope off Massachusetts, and Muir Seamount, located northeast of Bermuda.

Examination of these seamounts provides modern-day examples of several types of hard substrates. Examples of such substrates include: bare basalt outcrops and flows, manganese oxide cemented pavements, upright live or dead coral or sponge skeletons, coral fragments and rubble lying on the bottom, other biogenic structures (such as polychaete worm reefs), and glacial debris.

The use of manned submersibles, ROVs, and AUVs has provided insight into the spatial distribution and behaviors of various invertebrate groups associated with these hard substrates (e.g., gorgonian octocorals, stalked and unstalked crinoids, hexactinellid sponges, scleractinian corals and crustaceans). Concentrations of attached animals are often found in areas of localized higher flow regimes, on upright dead coral skeletons, near the edges of vertical structures, and along crests of linear features. In addition, many mobile suspension feeders (e.g., unstalked crinoids, brisingid sea stars, ophiacanthid brittle stars, and crustaceans) utilize elevated hard substrates, such as upright live or dead coral skeletons, to gain access to faster flow regimes above the benthic boundary layer.