Deep-water coral

Submarine communications cables and fishing methods such as bottom trawling tend to break corals apart and destroy reefs.

[2] Deep-water corals are enigmatic because they construct their reefs in deep, dark, cool waters at high latitudes, such as Norway's Continental Shelf.

[3] Early scientists were unsure how the reefs sustained life in the seemingly barren and dark conditions of the northerly latitudes.

Using one person submarines, a team of international scientists made 30 dives to depths of over 500 metres (1,600 ft) and saw giant coral forests, darting schools of fish, and a seafloor carpeted in brittle stars.

[12] 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.

Deep-water corals are widely distributed in Earth’s oceans, with large reefs/beds in the far North and far South Atlantic, as well as in areas with warmer water such as along 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, and Goniocorella 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).

Colonies of Enallopsammia contribute to the framework of deep-water coral banks found at depths of 600 to 800 metres (2,000–2,600 ft) in the Straits of Florida (Cairns and Stanley, 1982).

One of the most common species, Lophelia pertusa, lives in the Northeast and Northwest Atlantic Ocean, Brazil and off Africa’s west coast.

It lies between 300 and 400 metres (980 and 1,310 ft) deep, west of Røst island in the Lofoten archipelago, in Norway, inside the Arctic Circle.

At depths from 200 to 500 metres (660 to 1,640 ft), L. pertusa is chiefly on the Rockall Bank and on the shelf break north and west of Scotland.

[19] The Porcupine Seabight, the southern end of the Rockall Bank, and the shelf to the northwest of County Donegal all exhibit large, mound-like Lophelia structures.

South of Cape Lookout, NC, rising from the flat sea bed of the Blake Plateau, is a band of ridges capped with thickets of Lophelia.

These Lophelia communities lie in unprotected areas of potential oil and gas exploration and cable-laying operations, rendering them vulnerable to future threats.

[20] Lophelia exist around the Bay of Biscay, the Canary Islands, Portugal, Madeira, the Azores, and the western basin of the Mediterranean Sea.

Atlantic Frontier Environmental Network (AFEN) discovered them in 1998 while conducting large-scale regional sea floor surveys north of Scotland.

[21] Large congregations of Xenophyophores (Syringammina fragilissima) which are giant unicellular organisms that can grow up to 25 centimetres (9.8 in) in diameter characterize the tails and mounds.

[22] Oculina varicosa is a branching ivory coral that forms giant but slow-growing, bushy thickets on pinnacles up to 30 metres (98 ft) in height.

[23] Discovered in 1975 by scientists from the Harbor Branch Oceanographic Institution conducting surveys of the continental shelf, Oculina thickets grow on a series of pinnacles and ridges extending from Fort Pierce to Daytona, Florida[24][25][26] Like the Lophelia thickets, the Oculina Banks host a wide array of macroinvertebrates and fishes.

[27] Most corals must attach to a hard surface in order to begin growing but sea fans can also live on soft sediments.

As new growth surrounds the original, the new coral intercepts both water flow and accompanying nutrients, weakening and eventually killing the older organisms.

Deep-water coral colonies range in size from small and solitary to large, branching tree-like structures.

Trawlers drag nets across the ocean floor, disturbing sediments, breaking, and destroying deep-water corals.

A 2015 study revealed that observed injury in populations in the Mississippi Canyon in the Gulf of Mexico surged significantly after the Deepwater Horizon oil spill.

Deep-water corals have a slow growth rate, resulting in a much longer recovery period compared to shallow waters where nutrients and food-providing zooxanthellae are more abundant.

This study found that the corals were often broken in unnatural ways, and the ocean floor displayed scars and overturned boulders from trawling.

The International Council for the Exploration of the Sea, the European Commission’s main scientific advisor on fisheries and environmental issues in the northeast Atlantic, recommend mapping and closing Europe’s deep corals to fishing trawlers.