Coral reefs in the North Atlantic?

If you overheard somebody talking about coral reefs you would probably think of warm tropical seas with clear blue waters. However, some of the largest coral structures in the world are found in the cold and gloomy waters of the Northeast Atlantic.

Some individual Lophelia sub-structures are as high as 35 metres

Life in the dark
Lophelia is the dominant deepwater colonial coral in the North Atlantic. It is a true hard coral formed by a colony of individual coral polyps, which produce a calcium carbonate skeleton. It feeds by catching food from the surrounding water.

Unlike its tropical relatives, Lophelia does not need algae and light for survival and it is mainly found in deep water at depths between 200-1000 metres. The record for the deepest reef stands at 3000 m while the shallowest record of a living Lophelia reef is at 40 m in Trondheimsfjorden, Norway.

Cold water
Lophelia appears to prefer oceanic waters with temperatures between 4oC and 12oC and is found throughout the world's oceans, except in the polar regions. The highest density of Lophelia reefs is found in the ICES Area, within the Northeast Atlantic.

Elderly coral
Lophelia reefs grow at the rate of about 1 mm in height per year. The highest reefs found so far have been measured at an impressive 35 m, at Sula Ridge off the Norwegian coast. Fragments taken from this reef have been dated as being 8500 years old, which is just after the end of the last Ice Age.

Habitat for marine life
Lophelia reefs provide a shelter for hundreds of marine species. Amongst the coral branches occur fish (redfish, saithe, cod, ling, and tusk), squat lobsters, and other crustaceans, molluscs, starfish, brittlestars, sea pens, and sea urchins. A wide variety of animals grow on the coral itself, including sponges, bryozoans, hydroids, and other coral species.

Studies on four different Norwegian reefs have identified 744 species in total, but with only 15 species in common between the four sites. This indicates that the number of species on the reefs is much higher than described so far. The reefs have also traditionally been rich fishing grounds for longline and gillnet fisheries. Experimental fishing with longlines has shown that catches of redfish, Sebastes spp., are higher in coral habitats than in surrounding non-coral habitats.

Lophelia feed by catching food particles from the surrounding water

Large reef at Sula
The largest Lophelia reef that we have discovered in the North Atlantic is on the Sula Ridge on the mid-Norwegian shelf at 300 m. The reef has been mapped in great detail using Multibeam Swath Bathymetry.

This showed that the structure is more than 13 km long and up to 400 m wide. It consists of about 500 individual mounds, of which some are fused to form chains. The average height is about 15 m, but some individual sub-structures are as high as 35 m.

Threats against the reefs
The Institute of Marine Research in Bergen, Norway (www.imr.no/), has documented that Lophelia reefs are very sensitive to fishing activities using bottom trawls. It is estimated that 30-50 % of the Lophelia reefs in Norwegian waters have been damaged or impacted by trawling.

In 1999, the Norwegian Ministry of Fisheries issued regulations for the protection of coral reefs. An area of 1000 km2 at Sula, including the large reef, is now closed to bottom trawling.

Damage has also been reported from other parts of the ICES area, e.g. the Darwin Mounds northwest of Scotland, south of the Wyville-Thomson Ridge, and in the Porcupine seabight in Irish waters. In general, wherever bottom
trawling overlaps with occurrences of corals, there is a possibility of
damage.

Improving our understanding of cold-water corals
ICES has set up a Study Group on Mapping the Occurrence of Cold Water Corals in the Northeast Atlantic [SGCOR]. The group was formed after the European Commission asked ICES "to identify areas where cold-water corals may be affected by fishing.

Go to the Working Group reports

For further information about deep-sea coral reefs please try the following:
http://www.panda.org/downloads/gtte/norwayfinallr.pdf
http://www.imr.no/coral/
http://www.jncc.gov.uk/communications/news/darwinmounds.htm

Alternatively please contact the author:
Jan Helge Fosså
Institute of Marine Resarch
P.O. Box 1870 Nordnes
N-5817 Bergen
E-mail

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