The habitat of deep-water corals, also known as cold-water corals, extends to deeper, darker parts of the oceans than tropical corals, ranging from near the surface to the abyss, beyond 2,000 metres (6,600 ft) where water temperatures may be as cold as 4°C. Deep-water corals belong to the Phylum Cnidaria and are most often stony corals, but also include black and horny corals and soft corals including theGorgonians (sea fans). Like tropical corals, they provide habitat to other species, but deep-water corals do not require zooxanthellae to survive.
While there are nearly as many species of deep-water corals as shallow-water species, only a few deep-water species develop traditional reefs. Instead, they form aggregations called patches, banks, bioherms, massifs, thickets or groves. These aggregations are often referred to as “reefs,” but differ structurally and functionally. Deep sea reefs are sometimes referred to as “mounds,” which more accurately describes the large calcium carbonate skeleton that is left behind as a reef grows and corals below die off, rather than the living habitat and refuge that deep sea corals provide for fish and invertebrates. Mounds may or may not contain living deep sea reefs.
Submarine communications cables and fishing methods such as bottom trawling tend to break corals apart and destroy reefs. The deep-water habitat is designated as a United Kingdom Biodiversity Action Plan habitat.
Deep-water corals are widely distributed within the earth’s oceans, with large reefs/beds in the far North and far South Atlantic, as well as in the tropics in places such as the Florida coast. In the north Atlantic, the principal coral species that contribute to reef formation are Lophelia pertusa, Oculina varicosa, Madrepora oculata, Desmophyllum cristagalli,Enallopsammia rostrata, Solenosmilia variabilis, andGoniocorella dumosa. Four genera (Lophelia, Desmophyllum,Solenosmilia, and Goniocorella) constitute most deep-water coral banks at depths of 400–700 metres (1,300–2,300 ft)
Madrepora oculata occurs as deep as 2,020 m and is one of a dozen species that occur globally and in all oceans, including the Subantarctic (Cairns, 1982). Colonies of Enallopsammia contribute to the framework of deep-water coral banks found at depths of 600 to 800 m in the Straits of Florida (Cairns and Stanley, 1982).
(From the Deep Water Coral section of Wikipedia, May 31st, 2012)