Deep Water Corals Part II

What are Deep-water Corals?
General Distribution of Cold-water Corals
Two Important Deep-water Corals
Lophelia pertusa Distribution
Noted Lophelia Areas
Oculina varicosa Distribution
Threats to Lophelia and Oculina Corals
References

Reefs of Lophelia pertusa have been recorded on raised offshore seabeds in the north Atlantic off Britain and west Ireland. Map image: Marine Life Information Network (MarLIN).

The world's largest known deep-water Lophelia coral complex is the Røst Reef. It lies in depths between 300 and 400 m west of Røst Island in the Lofoten archipelago, Norway. Discovered during a routine survey in May 2002, the reef is still largely intact. It covers an area approximately 40 km long by 3 km wide.

Relatively close by is the Sula Reef, located on the Sula Ridge, west of trondheim on the mid-Norwegian Shelf, at 200 to 300 m depth. It is estimated to be 13 km long, 700 m wide, and up to 35 m high (Bellona Foundation, 2001), an area one-tenth the size of the 100 km2 Røst Reef.

Discovered and mapped in 2002, Norway's 1,000-year-old and 2-km-long Tisler Reef lies in the Skagerrak -- the submarine border between Norway and Sweden at a depth of 74 to 155 m. The Tisler Reef contains the world’s only known yellow Lophelia pertusa corals. At present, Norway is the only European nation to enact laws protecting its Lophelia reefs from trawling, pollution, and oil and gas exploration. However, the European Commission has introduced an interim ban on trawling in the Darwin Mounds area, west of Scotland, in August 2003. A permanent ban on trawling is expected to follow.

Elsewhere in the northeastern Atlantic, Lophelia is found around the Faroe Islands, an island group between the Norwegian Sea and the Northeast Atlantic Ocean. At depths from 200 to 500 m, Lophelia is chiefly on the Rockall Bank and on the shelf break north and west of Scotland (Tyler-Walters, 2003).

One of the most researched deep-water coral areas in the United Kingdom are the Darwin Mounds. The mounds were discovered in 1998 by the Atlantic Frontier Environmental Network (AFEN) while conducting large-scale regional surveys of the sea floor north of Scotland. They discovered two areas of hundreds of sand and cold-water coral mounds at depths of about 1,000 m, in the northeast corner of the Rockall trough, approximately 185 km northwest of the northwest tip of Scotland. Named after the research vessel Charles Darwin, the Darwin Mounds have been extensively mapped using low-frequency side-scan sonar. They cover an area of approximately 100 km2 and consist of two main fields -- the Darwin Mounds East, with about 75 mounds, and the Darwin Mounds West, with about 150 mounds. Other mounds are scattered in adjacent areas. Each mound is about 100 m in diameter and 5 m high.

Two images of the deep sea coral Lophelia pertusa. The image on the left shows the complex growth structure of a small colony. On the right is a closeup of individual polyps. Photo: John Reed, 2002a.

The tops of the mounds are covered with Lophelia corals and coral rubble, which attract other marine life. Side-scan sonar images show that the mounds appear to be sand volcanoes, each with a unique feature -- a “tail.” The tails are up to several hundred m long, all oriented downstream (ICES, 2001a). The tails and the mounds are uniquely characterized by large congregations of deep-sea organisms called xenophyophores (Syringammina fragilissima), which are giant unicellular organisms that can grow up to 25 cm in diameter (ICES, 2002). Scientists are uncertain why these interesting organisms congregate in these areas. In addition, the Lophelia of the Darwin Mounds are growing on sand rather than hard substrate, an unusual condition unique to this area. Usually, coral larvae almost always settle and grow on hard substrates, such as dead coral skeletons or rock.

Lophelia corals exist in Irish waters as well (Rogers, 1999). The Porcupine Seabight, the southern end of the Rockall Bank, and the shelf to the northwest of Donegal all exhibit large, mound-like Lophelia structures. One of them, the Theresa Mound, is particularly noted for its Lophelia pertusa and Madrepora oculata colonies. Lophelia reefs are also found along the U.S. East Coast at depths of 500 to 850 m along the base of the Florida-Hatteras slope. 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 are the northernmost East Coast Lophelia pertusa growths. The coral mounds and ridges here rise as much as 150 m from the plateau plain. These Lophelia communities lie in unprotected areas of potential oil and gas exploration and cable-laying operations, rendering them vulnerable to future threats (Sulak and Ross, 2001).

Finally, Lophelia is known to exist around the Bay of Biscay, the Canary Islands, Portugal, Madeira, the Azores, and the western basin of the Mediterranean Sea. (ICES, 2001a).

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Oculina varicosa is a branching ivory coral that forms giant but slow-growing, bushy thickets on pinnacles up to 30 m in height. The Oculina Banks, so named because they consist mostly of Oculina varicosa, exist in 50 to 100 m of water along the continental shelf edge about 26 to 50 km off of Florida's central east coast.
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 (Avent et al, 1977; Reed, 1981; Reed, 2000a,b).

Like the Lophelia thickets, the Oculina Banks host a wide array of macroinvertebrates and fishes. They also are significant spawning grounds for commercially important species of food fishes including gag, scamp, red grouper, speckled hind, black sea bass, red porgy, rock shrimp, and the calico scallop (Koenig et al., on-line).


Both Lophelia and Oculina corals face uncertain futures. Until recently, Lophelia habitats remained undisturbed by human activity. However, as traditional fish stocks are depleted from northern European waters, bottom trawling has moved into deeper waters, where the gear has affected the coral beds. The towed nets break up the reef structure, kill the coral polyps and expose the reef to sediment by altering the hydrodynamic and sedimentary processes around the reef (Hall-Spencer et al., 2002).

The fishes and invertebrates that depend on the coral structure lose their habitat and move out of the area. Damage may range from a decrease in the size of the coral habitat with a corresponding decrease in the abundance and biodiversity of the associated invertebrate and fish species, to the complete destruction of the coral habitat. The trawls also may resuspend sediments that, in turn, may smother corals growing downstream of the current. In addition, oil and gas exploration and extraction operations have begun to move into these deep-water areas, further threatening the resident corals.

Two images of the deep-sea copral Oculina varicosa. The image on the left shows the complex growth structure of a small colony. On the right is a closeup of an individual branch. Photo: John Reed, 2002a.

Scientists estimate that within the Norwegian Exclusive Economic Zone, 30 to 50 percent of the total coral area of the Norwegian shelf has been damaged or destroyed by trawling (Fossa, 2002). Scientists from the International Council for the Exploration of the Sea, the main provider of scientific advice to the European Commission on fisheries and environmental issues in the northeast Atlantic, have recommended that to protect the remaining deep-water coral groves, all of Europe’s deep corals must be accurately mapped and then closed to fishing trawlers (ICES, 2001b).

In 1999, the first complete mapping of the Sula Reef was carried out by the Norwegian Hydrographic Society, which used the latest available multibeam echosounder equipment to record both depth and backscatter data. The mapping was the product of joint cooperation between the Geological Survey of Norway and the Institute of Marine Research. That same year, the Norwegian Ministry of Fisheries issued regulations for the protection of the Lophelia reefs. An area of 1,000 km2 at Sula, including the large reef, is now closed to bottom trawling. In 2000, an additional area, about 600 km2 was closed. The Røst Reef, an area of about 300 km2, was closed to bottom trawling in 2002.

Florida's Oculina Banks, once teeming with commercially important fish, now appear to be severely depleted of fish stocks (MPA, 2002). Much of the Oculina coral has been reduced to rubble, probably the result of a combination of destructive bottom trawling and natural causes like bioerosion and episodic die-offs. Regardless of the cause, the Oculina Banks now support a drastically reduced fishery because most of the significant spawning grounds have been destroyed (Reed, 2000a,b).

This beautiful species of Madrepora oculata coral was collected off the coast of South Carolina.

Efforts to protect the Oculina Banks began in 1980, when scientists from Harbor Branch Oceanographic Institution initiated a call to implement protective measures for the area. Since then, progressively stricter legal protections have been implemented to facilitate a recovery. In 1984, a 315 km2 portion of deep-water Oculina reef system was designated as a Habitat Area of Particular Concern by the South Atlantic Fishery Management Council (Reed, 2000a,b), a designation that categorized it as an area of special ecological significance worthy of stricter regulatory and enforcement activity.

In 1994, after the area showed no significant recovery, part of the Oculina Banks was completely closed to bottom fishing in an area called the Experimental Oculina Research Reserve. In 1996, the South Atlantic Fisheries Management Council implemented additional protections in the reserve by prohibiting fishing vessels from dropping anchors, grapples, or attached chains there. In 1998, the council also designated the reserve as an Essential Fish Habitat. In 2000, the deep-water Oculina Marine Protected Area was extended to 1029 km2 (NOAA, 2000; Reed, 2000a,b).

The Oculina Banks remain a hot spot for research and efforts to rehabilitate the coral (MPA, 2002). Scientists recently deployed concrete “reef balls” in the area in an attempt to attract fish and provide substrate for coral attachment, settlement and growth. They are cautiously optimistic about their initial restorative efforts in the reserve (MPA, 2002).


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References and Additional Readings

Atlantic Coral Ecosystem Study (ACES), 2000. Consortium of European scientists completed an environmental assessment of the status of Europe’s deep-water corals, available on-line at: http://www.cool-corals.de

Avent, R.M., M.E. King, and R.M. Gore. 1977. Topographic and faunal studies of shelf-edge prominences off the central eastern Florida coast. Int. Revue ges.Hydrobiol. 62:185-208.

Bell, N. and J. Smith. 1999. Coral growing on North Sea oil rigs. Nature 402:601.

Bellona Foundation. 2001. Coral reefs in Norwegian Waters. Available on-line at http://www.bellona.no/en/b3/biodiversity/
coral_reefs/12784.html.

Cairns, S.D. 1982. Antarctic and Subantarctic Scleractinia. Antarctic Research Series 34: 74 pp.

Cairns, S. and G. Stanley. 1982. Ahermatypic coral banks: Living and fossil counterparts. Proceedings of the Fourth International Coral Reef Symposium, Manila (1981), 1: 611-618.

Fossa, J.H., P.B. Mortensen, and D.M. Furevic. 2002. The deep-water coral Lophelia pertusa in Norwegian waters: distribution and fishery impacts. Hydrobiologia 417: 1-12. Available on-line at: http://www.imr.no/dokumenter/fossa.pdf

Hall-Spencer, J. et al. 2002. trawling damage to Northeast Atlantic ancient coral reefs. Proc. R. Soc. London B.

Hoskin, C.M., J.K. Reed, and D.H. Mook. 1987. Sediments from a living shelf-edge reef and adjacent area off central eastern Florida. Pp. 42-77, In: F, JMR,Maurrasse (ed.), Symposium on south Florida geology. Miami Geological Society. Memoirs 3.

International Council for Exploration of the Sea (ICES). 2001a. Marine World, article on deep-sea coral. Available on-line at http://www.ices.dk/marineworld/deepseacoral.asp

International Council for Exploration of the Sea (ICES). 2001b. Close Europe’s cold-water coral reefs to fishing. Available on-line at http://www.ices.dk/aboutus/pressrelease/coral.asp

International Council for Exploration of the Sea (ICES). 2001c: Extract of the report of the Advisory Committee on Ecosystems 2002 on identification of areas where cold-water corals may be affected by fishing.

International Council for Exploration of the Sea (ICES). 2002. Advisory Committee on Ecosystems. Report of the study group on mapping the occurrence of cold-water corals: 1-17.

Koenig, C., C.F. Coleman, and S. Brooke. Coral restoration in the Experimental Oculina Research Reserve of the South Atlantic. Available on-line at
http://www.bio.fsu.edu/ifre/ifre_research_oculina.html

Marine Protected Areas of the United States (MPA). 2002. Experimental Oculina Research Reserve. Available on-line at http://mpa.gov/what_is_an_mpa/oculina.html

Mayer, T. 2001. 2000 Years Under the Sea. Available on-line at http://exn.ca/Stories/2001/10/16/52.asp

National Oceanic and Atmospheric Administration. 2000. Final Rule, Amendment 4 to the Fishery Management Plan for Coral, Coral Reefs, and Live/Hard Bottom Habitats of the South Atlantic Regions (Coral FMP). Federal Register, Vol. 65, No. 115, June 14, 2000.

National Oceanic and Atmospheric Administration. 1982. Fishery Management Plan for Coral and Coral Reefs of the Gulf of Mexico and South Atlantic. Gulf of Mexico and South Atlantic Fishery Management Councils.

Reed, J.K. 1981. In Situ growth rates of the scleractinian coral Oculina varicosa occurring with zooxanthellae on 6-m reefs and without on 80-m banks. pp. 201-206. in: W.J. Richards (ed.), Proceedings of Marine Recreational Fisheries Symposium.

Reed, J.K. 2002a. Comparison of deep-water coral reefs and lithoherms off southeastern U.S.A. Hydrobiologia 471: 43-55.

Reed, J.K. 2002b. Deep-water Oculina reefs of Florida: biology, impacts and management. Hydrobiologia 471:43-55.

Reed, J.K. and C.M. Hoskin. 1984. Studies of geological and biological processes at the shelf-edge with use of submersibles. In: Undersea research and technology – Scientific application and future needs – abstracts, Symposia Series for Undersea Research, Vol. 2, NOAA.

Reed, J.K., R.H. Gore, L.E. Scotto and K.A. Wilson. 1982. Community composition, structure,aerial and trophic relationships of decapods associated with shallow and deep-water Oculina varicosa coral reefs. Bull. Mar. Sci. 32:761-786.

Rogers, A.D. 1999. The biology of Lophelia pertusa (Linnaeus 1758) and other deep-water reef-forming corals and impacts from human activities. International Review of Hydrobiology 84: 315–406.

Rogers, A., M. Le Goff, and B. Stockley. Ecology of deep-water stoney corals (the Darwin Mounds). Available on-line at http://www.soton.ac.uk/~merg/corals.htm

Southampton Oceanographic Centre. Coral ecosystems in deep water. Available on-line at
http://www.soc.soton.ac.uk/GDD/DEEPSEAS/
coralecosystems.html

Sulak, K. and S. Ross. 2001. A profile of the Lophelia reefs. Available on the NOAA Ocean Explorer Web site at http://oceanexplorer.noaa.gov/explorations/islands01/
background/islands/sup10_lophelia.html.

Tyler-Walters, H. 2003. Lophelia reefs. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme. Plymouth: Marine Biological Association of the United Kingdom. Available on-line at http://www.marlin.ac.uk/biotopes/bio_basicinfo_COR.Lop.htm


Watling, L. 2001. Deep sea coral. Available on the NOAA Ocean Explorer Web site at http://oceanexplorer.noaa.gov/explorations/deepeast01/
background/corals/corals.html.


Williams, G.C. 2001. Octocoral Research Center Web Site. Available on-line at
http://www.calacademy.org/research/
izg/orc_home.html

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