Cold Water Corals

Overview

Coral reefs are commonly assumed to be rich, high biodiversity ecosystems in warm, shallow seas. Whilst in some cases this is certainly true, coral reefs can also be found at depth, in dark and cold regions of the world ocean.

Lophelia pertusa overgrown with sponge. Photo: T Lundalv, Tjarno Marine Biological Laboratory

For several hundred years fragments of broken coral have occasionally turned up in the nets of European fishermen, indicating the existence of the coral communities. It has only been over the last 25 years or so that concerted efforts have been made by the scientific community to understand these hidden ecosystems.

Assigning a name to these corals has been problematic. Some investigators have referred to them as 'deep water corals', others as 'cold water corals'. The consensus is favoring the term 'cold water corals', as although often found at depth, they have been found to occur very close to the surface in some locations. 'Cold water corals' is the term we will use here.

Like shallow water corals, cold water corals are formed of a calcareous skeleton built up by a polyp community living within. Unlike the shallow water corals, these cold water corals lack the algal symbionts (the zooxanthellae) which provide a large food input for the shallow corals. The lack of these symbionts means that cold water corals have to rely wholly on organic material (detritus from surface waters and zooplankton) for their energy supply.

Cold water coral ecosystems have now been found in many locations, in the Atlantic, Pacific and Indian Oceans. In many cases these are found along the continental margin, usually on regions of raised seabed, such as on seamounts, mounds or sills.

A number of cold water coral reef species have been discovered, a number of which build large reef structures. These reef structures have been found to be important habitats for many fish species, and particularly juvenile fish. These discoveries are recent and protection of these 'coral nurseries' has been variable from nation to nation.

 

Map of known Lophelia pertusa cold water coral distribution. NOC, Southampton

 

Trawl damage has been extensive at many reefs, both unwitting accidential damage and deliberate attempts to increase catches by breaking up reefs. Damage as in the image below is typical:-

Trawl damage to Lophelia pertusa reef on Norwegian continental shelf. Photo: ICES report, 2002

Norway is unique in the degree of protection it offers to such habitats, with the Tisler Reef being one of those protected.

Of the reef building cold water coral species, Lophelia pertusa is the most widespread, and the predominant coral found at the Tisler reef sample site.

 

The Tisler reef

The Tisler reef is located on a sill in the narrow channel connecting the Kosterfjord and the rest of the Skagerrak, at a depth of about 120m. The rough location can be seen on the map below.

 

 

 

 

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