Deep-water coral

Lore & Background

Deep-water corals were first discovered by fishermen about 250 years ago, which garnered interest from scientists. Early scientists were unsure how the reefs sustained life in the seemingly barren and dark conditions of northerly latitudes. It was not until modern times, when crewed mini-submarines first reached sufficient depth, that scientists began to understand these organisms. Pioneering work by Wilson (1979) shed light on a colony on the Porcupine Bank, off Ireland. The first ever live video of a large deep-water coral reef was obtained in July 1982, when Statoil surveyed a 15 metres tall and 50 metres wide reef perched at 280 metres water depth near Fugløy Island, north of the Polar Circle, off northern Norway.

During their survey of the Fugløy reef, Hovland and Mortensen also found seabed pockmark craters near the reef. Since then, hundreds of large deep-water coral reefs have been mapped and studied. About 60 percent of the reefs occur next to or inside seabed pockmarks. Because these craters are formed by the expulsion of liquids and gases (including methane), several scientists hypothesize that there may be a link between the existence of the deep-water coral reefs and nutrient seepage through the seafloor, a hypothesis called the 'hydraulic theory' for deep-water coral reefs.

Deep-water corals are widely distributed in Earth's oceans, with large reefs in the far North and far South Atlantic, as well as in warmer waters such as along the Florida coast. Principal reef-forming species include Lophelia pertusa, Oculina varicosa, Madrepora oculata, Desmophyllum cristagalli, Enallopsammia rostrata, Solenosmilia variabilis, and Goniocorella dumosa. The world's largest known deep-water Lophelia coral complex is the Røst Reef, discovered in May 2002, lying between 300 and 400 metres deep west of Røst island in Norway's Lofoten archipelago.

Reader's Guide

Deep-water corals provide habitat to other species, similar to tropical corals, but they do not require zooxanthellae. Their aggregations are often called 'reefs' but differ structurally and functionally; the term 'mounds' more accurately describes the large calcium carbonate skeleton left behind as a reef grows and corals below die off. 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.

Lophelia communities support diverse marine life, including sponges, polychaete worms, mollusks, crustaceans, brittle stars, starfish, sea urchins, bryozoans, sea spiders, fish, and many other vertebrate and invertebrate species. The first international symposium for deep-water corals took place in Halifax, Canada in 2000, considering all aspects including protection methods. In June 2009, the Living Oceans Society led the Finding Coral Expedition on Canada's Pacific coast, using one-person submarines to make 30 dives to depths over 500 metres, identifying 16 species of corals. This research was the culmination of five years of work to secure protection from the Canadian Government for these slow-growing and long-lived animals, which provide critical habitat for fish and other marine creatures.

Among the most researched deep-water coral areas in the United Kingdom are the Darwin Mounds, discovered in 1998 by the Atlantic Frontier Environmental Network during regional sea floor surveys north of Scotland. They consist of hundreds of sand and deep-water coral mounds at depths of about 1,000 metres in the northeast corner of the Rockall Trough, covering approximately 100 square kilometres.

Did You Know?

• Deep-water corals can live in water as cold as 4 °C (39 °F) and at depths beyond 2,000 metres (6,600 ft).
• About 60 percent of deep-water coral reefs occur next to or inside seabed pockmarks, which are formed by the expulsion of liquids and gases including methane.