The western North Atlantic Ocean between Cape Hatteras and Cape Cod (USA, Middle Atlantic Bight, MAB) is characterised by numerous and diverse submarine canyons that straddle the outer shelf and slope. Research interests in these canyons and associated ecosystems have increased in the last 20 years, largely in response to potential energy exploration and development. This ATLAS case study focuses on the area between Baltimore Canyon and Cape Hatteras, but also draws on relevant data from recent studies on the Blake Plateau off the southeastern US. This area represents a unique transition from the rocky and carbonate bottom Blake Plateau that is oceanographically dominated by the Gulf Stream to the softer sediment, canyon dominated area north of Cape Hatteras, influenced by colder currents.

Extensive recent studies in and around Baltimore and Norfolk canyons revealed that the physical environment in the canyons was different from that on the open slope, that it varied over relatively small spatial scales, and that the oceanography and geology have great influence on the character of the benthic community, especially sessile invertebrates (corals, sponges, infauna). These canyons provided extensive rugged, hard substrata habitats that supported diverse deep-sea coral communities, although most of the mobile fauna was influenced by habitat structure and not presence or absence of corals. Newly discovered methane seeps in this area also supported both chemosynthetic communities and a variety of other organisms drawn to habitat structure derived from the seeps. In addition to habitat attributes, depth was a major factor structuring communities in and around the canyons.

Anthropogenic impacts (trash, discarded fishing gear, etc.) were widely observed, especially near the heads of Baltimore and Norfolk canyons. Even so, the rugged canyon and seep habitats provided refuge for a number of exploited species (e.g., American lobster, squids, cusk [tusk], sharks). Because of the high productivity, fragile habitats, presence of corals, and vulnerability to impact, the MAB canyons and surroundings were recently given protected area status by US agencies.

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