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* http://www.mar.dfo-mpo.gc.ca/communications/maritimes/back02e/B-MAR-02-(5E).html. Fisheries and Oceans Canada. Retrieved on 2008-March -30.
* http://www.mar.dfo-mpo.gc.ca/communications/maritimes/back02e/B-MAR-02-(5E).html. Fisheries and Oceans Canada. Retrieved on 2008-March -30.
* Roberts S, Hirshfield M. (2004) [http://www.oceana.org/fileadmin/oceana/uploads/destructive_trawling/savecorals/News/oceana_coral_report_old.pdf Deep Sea Corals: Out of Sight, But No Longer Out of Mind]. Oceania. In Frontiers in Ecology and the Environment, April 2004.
* Roberts S, Hirshfield M. (2004) [http://www.oceana.org/fileadmin/oceana/uploads/destructive_trawling/savecorals/News/oceana_coral_report_old.pdf Deep Sea Corals: Out of Sight, But No Longer Out of Mind]. Oceania. In Frontiers in Ecology and the Environment, April 2004.
http://www.findingcoral.com Living Oceans Society expedition to discover cold water corals off the coast of British Columbia
* http://www.findingcoral.com Living Oceans Society expedition to discover cold water corals off the coast of British Columbia


[[Category:Anthozoa]]
[[Category:Anthozoa]]

Revision as of 22:30, 16 June 2009

Deep Water Coral, also known as cold water coral, are found worldwide. They live in deeper, darker parts of the oceans than tropical corals. Deep Water Corals belong to the Phylum Cnidaria and are most often stony corals. These corals are similar to tropical corals in that they are important habitats to other species and organisms of the ocean. Cold water corals differ from tropical species in that they do not require zooxanthellae to survive.

Some of the largest cold water coral reefs include the Rosta Reef and the Sula Ridge Complex found off the coast of Norway, while the Røst Reef southwest of Lofoten, nearly 40 km long, is the largest known. One of the most common cold water corals is Lophelia pertusa. Often these corals are found by fishermen as well as companies searching for oil and gas in the oceans.

Cold water corals are currently being negatively affected by fishing methods such as deep water trawling and long line systems. These methods tend to break corals apart and destroy reefs.

Discovery and Study

Deep-water corals are enigmatic because they construct their reefs in the deep, dark, cool waters of high latitudes, such as the Continental Shelf of Norway. They were first discovered by fishermen about 250 years ago, and became known to scientists then (Gunnerus, 1768). However, as the early scientists could never figure out how they sustained life in the barren and dark north, they were treated as mere curiosities of biology. It was not before modern times, when they were first surveyed and viewed, using manned mini-submarines in their proper environment, they were taken more seriously by marine biologists. John B. Wilson (1979) pioneered this work and found out how they lived on the Porcupine Bank, off Ireland. The first ever live video-footage of a large deep-water coral reef was obtained in July, 1982, when Statoil surveyed a 15 m tall and 50 m wide reef perched at 280 m water depth near Fugløy island, north of the Polar Circle, off northern Norway (see Hovland, 2008).

During their survey of the Fugløy reef, Hovland and Mortensen (1999) also found some seabed pockmark craters nearby 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 actually form inside seabed pockmarks (King and MacLean, 1970; Judd and Hovland, 2007). Because these craters are formed by the expulsion of liquids and gases (including methane), several scientists have entertained the idea that there may be a link between the existence of the deep-water coral reefs and seepage of nutrients (light hydrocarbons, such as methane, ethane, and propane) through the seafloor. This hypothesis is called the 'hydraulic theory' for deep-water coral reefs (Hovland and Thomsen, 1997; Hovland and Risk, 2003).

Taxonomy

Table Coral, which can live in deep water (in this picture, it is in shallow, warm water)
Soft hexacoral

Corals are animals the phylum Cnidaria and the class Anthozoa. Anthozoa is broken down into two subclasses Octocorals and Hexacorals. Octocorals are soft corals such as sea pens. Hexacorals are where sea anemones and hard bodied corals belong. Octocorals contain eight body extensions whereas Hexacorals have six. Most deep water corals are stony corals and therefore belong to the subclass Hexacorals. As previously mentioned, Lophelia pertusa is an example of a stony coral.

Distribution

The knowledge of deep water coral has mostly come from fishing companies and other organizations. Cold water coral are widely distributed within the earth’s oceans. The coral reef building species have specific requirements that determine where they are able to build their reefs. They require a hard surface to attach to in order to begin growing. This is why they are often found growing on seamounts, continental slopes or even rocks. Corals are sedentary organisms and so they must live near nutrient rich water currents. Cold water corals feed on zooplankton and so they rely on ocean currents to bring them their food. The currents also aid in keeping the coral clean.

The depth of water in which deep water corals live varies from one species to another. Some species live in waters as little as 40 meters deep and other species have been found as deep as 1500 meters below the surface.

One of the common species, Lophelia pertusa, is found in the Northeast Atlantic Ocean, the eastern coast of the United States and Brazil as well as off the west coast of Africa. They are found all across the world and it is expected that there are many existing reefs that have not yet been found.

Growth and Reproduction

Deep water corals have not been studied in great detail so there are some facts about them that remain unknown. They tend to grow slower than tropical corals because they do not receive the sunlight tropical species do. The dominant life form of corals is the polyp. As in every living organism food is essential for growth. Deep water corals have tentacles located on their polyp which aid in capturing food by the use of nematocysts which stun the prey. Cold water corals feed on zooplankton, crustaceans and even krill.

Lophelia pertusa is a species of deep water coral where each colony is either female or male. Deep water corals can reproduce sexually or asexually. In asexual reproduction they simply produce a bud of their existing body that falls off. Sexual reproduction requires an egg and sperm meeting which produces larvae. These larvae are carried by ocean currents and growth begins when they attach to a solid substrate. As the coral reproduces and more new growth surrounds the original coral, the middle corals begin to die off due to a lack of nutrients and water flow. New material tends to grow on the dying matter which creates reefs of great depths.

The species Lophelia pertusa grows approximately 5-25 millimetres per year. Some of the largest deep water reefs have been found in the North Atlantic Ocean off the coast of Norway. The Sula Ridge reef is up to 14 km long and up to 35 metres in height. Another reef, the Rosta, is the largest known today and is 40 km long and 2 to 3 km in width.

Importance

Deep water corals play an important role in the ocean. They are very similar to the tropical corals in that they host a large variety of species. Fish and crustaceans live in new and dead corals. A fish often found in deep water corals is the redfish. In some cases Lophelia reefs are home to up to 1300 species of fish and invertebrates.

Human Impacts

Deep water corals currently and in the past have been damaged by deep water trawling. Recently fishermen have had to fish deeper in the ocean to catch their fish. Trawling is the process when fishermen drag their nets across the ocean floor. This causes sediments to mix and it breaks apart the deep water corals. Other methods that are negatively affecting the corals are the use of long lines for fishing as well as searching for oil and gas within the oceans.

The deep water corals as previously mentioned are slow growing, and so human activities such as trawling are negatively impacting the corals in that corals are being destroyed faster than they can grow back to their original size.

In a recent study during 2001 to 2003, on deep water corals in Atlantic Canada, a reef of Lophelia pertusa was studied and it was found that the corals were often broken in ways that they do not naturally break. As further evidence there were also scars in the ocean floor, the remnants of a trawling net as well as overturned boulders.

It is currently a battle between fishermen and conservation efforts to protect deep water corals. The first international symposium for deep water corals took place in Halifax, Canada in 2000. At this symposium all aspects of deep water corals were discussed, including methods to protect the corals. These efforts include banning deep water trawling and in some cases some reefs and areas of coral growth have been protected.

See also

Coral Reefs, for an in depth description of anatomy and reproduction of corals.

References

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