The habitat of deep-water corals, also known as cold-water corals, extends to deeper, darker parts of the oceans than tropical corals, ranging from near the surface to the abyss, beyond 2,000 metres (6,600 ft) where water temperatures may be as cold as 4 °C (39 °F). Deep-water corals belong to the Phylum Cnidaria and are most often stony corals, but also include black and horny corals and soft corals including the Gorgonians (sea fans). Like tropical corals, they provide habitat to other species, but deep-water corals do not require zooxanthellae to survive.
While there are nearly as many species of deep-water corals as shallow-water species, only a few deep-water species develop traditional reefs. Instead, they form aggregations called patches, banks, bioherms, massifs, thickets or groves. These aggregations are often referred to as "reefs," but differ structurally and functionally. Deep sea reefs are sometimes referred to as "mounds," which more accurately describes the large calcium carbonate skeleton that is left behind as a reef grows and corals below die off, rather than the living habitat and refuge that deep sea corals provide for fish and invertebrates. Mounds may or may not contain living deep sea reefs.
Submarine communications cables and fishing methods such as bottom trawling tend to break corals apart and destroy reefs. The deep-water habitat is designated as a United Kingdom Biodiversity Action Plan habitat.
Deep-water corals are enigmatic because they construct their reefs in deep, dark, cool waters at high latitudes, such as Norway's Continental Shelf. They were first discovered by fishermen about 250 years ago, which garnered interest from scientists. Early scientists were unsure how the reefs sustained life in the seemingly barren and dark conditions of the northerly latitudes. It was not until modern times, when manned mini-submarines first reached sufficient depth, that scientists began to understand these organisms. Pioneering work by Wilson (1979) shed light on a colony on the Porcupine Bank, off Ireland. The first ever live video of a large deep-water coral reef was obtained in July, 1982, when Statoil surveyed a 15 metres (49 ft) tall and 50 metres (160 ft) wide reef perched at 280 metres (920 ft) water depth near Fugløy Island, north of the Polar Circle, off northern Norway.
During their survey of the Fugløy reef, Hovland and Mortensen also found seabed pockmark craters near 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 inside seabed pockmarks. Because these craters are formed by the expulsion of liquids and gases (including methane), several scientists hypothesize that there may be a link between the existence of the deep-water coral reefs and nutrients seepage (light hydrocarbons, such as methane, ethane, and propane) through the seafloor. This hypothesis is called the 'hydraulic theory' for deep-water coral reefs.
Lophelia communities support diverse marine life, such as sponges, polychaete worms, mollusks, crustaceans, brittle stars, starfish, sea urchins, bryozoans, sea spiders, fish and many other vertebrate and invertebrate species.
The first international symposium for deep-water corals took place in Halifax, Canada in 2000. The symposium considered all aspects of deep-water corals, including protection methods.
In June 2009, Living Oceans Society led the Finding Coral Expedition on Canada’s Pacific coast in search of deep sea corals. 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. During expedition, scientists identified 16 species of corals. This research trip 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.
Corals are animals in the phylum Cnidaria and the class Anthozoa. Anthozoa is broken down into two subclasses Octocorals (Alcyonaria) and Hexacorals (Zoantharia). Octocorals are soft corals such as sea pens. Hexacorals include sea anemones and hard bodied corals. Octocorals contain eight body extensions while Hexacorals have six. Most deep-water corals are stony corals.
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 the tropics in places such as 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).
Madrepora oculata occurs as deep as 2,020 metres (6,630 ft) and is one of a dozen species that occur globally and in all oceans, including the Subantarctic (Cairns, 1982). 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).
The world's largest known deep-water Lophelia coral complex is the Røst Reef. 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. Discovered during a routine survey in May 2002, the reef is still largely intact. It is approximately 35 kilometres (22 mi) long by 3 kilometres (1.9 mi) wide.
Some 500 kilometres (310 mi) further south is the Sula Reef, located on the Sula Ridge, west of Trondheim on the mid-Norwegian Shelf, at 200–300 metres (660–980 ft). It is 13 kilometres (8.1 mi) long, 700 metres (2,300 ft) wide, and up to 700 metres (2,300 ft) high, an area one-tenth the size of the 100 square kilometres (39 sq mi) Røst Reef.
Discovered and mapped in 2002, Norway's Tisler Reef lies in the Skagerrak on the submarine border between Norway and Sweden at a depth of 90–120 metres (300–390 ft) and covers an area of 2 by 0.2 kilometres (1.24 mi × 0.12 mi). It is estimated to be 8600–8700 years old. The Tisler Reef contains the world’s only known yellow L. pertusa. 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 metres (660 to 1,640 ft), L. pertusa is chiefly on the Rockall Bank and on the shelf break north and west of Scotland. 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 Therese 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 500–850 metres (1,640–2,790 ft) 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 metres (490 ft) 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.
Lophelia exist around the Bay of Biscay, the Canary Islands, Portugal, Madeira, the Azores, and the western basin of the Mediterranean Sea.
Among the most researched deep-water coral areas in the United Kingdom are the Darwin Mounds. Atlantic Frontier Environmental Network (AFEN) discovered them in 1998 while conducting large-scale regional sea floor surveys north of Scotland. They discovered two areas of hundreds of sand and deep-water coral mounds at depths of about 1,000 metres (3,300 ft) in the northeast corner of the Rockall Trough, approximately 185 kilometres (115 mi) 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 square kilometres (39 sq mi) 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 metres (330 ft) in diameter and 5 metres (16 ft) high. Lophelia corals and coral rubble cover the mound tops, attracting other marine life. The mounds look like 'sand volcanoes', each with a 'tail', up to several hundred meters long, all oriented downstream. 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. Scientists are uncertain why these organisms congregate here. The Darwin Mounds Lophelia grow on sand rather than hard substrate, unique to this area. Lophelia corals exist in Irish waters as well.
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. The Oculina Banks, so named because they consist mostly of Oculina varicosa, exist in 50–100 metres (160–330 ft) of water along the continental shelf edge about 42–80 km (26–50 miles) off of Florida's central east coast. The Oculina Banks stretch along 170 kilometers (106 miles) reaching from Fort Pierce to Daytona.
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 Like the Lophelia thickets, the Oculina Banks host a wide array of macroinvertebrates and fishes. They are significant spawning grounds for commercially important food species including gag, scamp, red grouper, speckled hind, black sea bass, red porgy, rock shrimp, and calico scallop.
Most corals must attach to a hard surface in order to begin growing but sea fans can also live on soft sediments. They are often found growing along bathymetric highs such as seamounts, ridges, pinnacles and mounds, on hard surfaces. Corals are sedentary, so they must live near nutrient-rich water currents. Deep-water corals feed on zooplankton and rely on ocean currents to bring food. The currents also aid in cleaning the corals.
Deep-water corals grow more slowly than tropical corals because there are no zooxanthellae to feed them. Lophelia has a linear polyp extension of about 10 millimetres (0.39 in) per year. By contrast, branching shallow-water corals, such as Acropora, may exceed 10–20 cm/yr. Reef structure growth estimates are about 1 millimetre (0.039 in) per year. Scientists have also found Lophelia colonies on oil installations in the North Sea. Using coral age-dating methods, scientists have estimated that some living deep-water corals date back at least 10,000 years.
Coral can reproduce sexually or asexually. In asexual reproduction (budding) a polyp divides in two genetically identical pieces. Sexual reproduction requires that a sperm fertilize an egg which grows into a larva. Currents then disperse the larvae. Growth begins when the larvae attach to a solid substrate. Old/dead coral provides an excellent substrate for this growth, creating ever higher mounds of coral. As new growth surrounds the original, the new coral intercepts both water flow and accompanying nutrients, weakening and eventually killing the older organisms.
Individual Lophelia pertusa colonies are entirely either female or male.
Deep-water coral colonies range in size from small and solitary to large, branching tree-like structures. Larger colonies support many life forms, while nearby areas have much less. The gorgonian, Paragorgia arborea, may grow beyond three meters. However, little is known of their basic biology, including how they feed or their methods and timing of reproduction.
Deep sea corals together with other habitat-forming organisms host a rich fauna of associated organisms. Lophelia reefs can host up to 1,300 species of fish and invertebrates. Various fish aggregate on deep sea reefs. Deep sea corals, sponges and other habitat-forming animals provide protection from currents and predators, nurseries for young fish, and feeding, breeding and spawning areas for numerous fish and shellfish species. Rockfish, Atka mackerel, walleye pollock, Pacific cod, Pacific halibut, sablefish, flatfish, crabs, and other economically important species in the North Pacific inhabit these areas. Eighty-three percent of the rockfish found in one study were associated with red tree coral. Flatfish, walleye pollock and Pacific cod appear to be more commonly caught around soft corals. Dense schools of female redfish heavy with young have been observed on Lophelia reefs off Norway, suggesting the reefs are breeding or nursery areas for some species. Oculina reefs are important spawning habitat for several grouper species, as well as other fishes.
The primary human impact on deep-water corals is from deep-water trawling. Trawlers drag nets across the ocean floor, disturbing sediments, breaking and destroying deep-water corals. Another harmful method is long line fishing.
Oil and gas exploration also damage deep-water coral. A study conducted in 2015 found that injury observed in populations in the Mississippi Canyon in the Gulf of Mexico increased from 4 to 9 percent before the Deepwater Horizon oil spill to 38 to 50 percent after the spill (Etnoyer et al., 2015).
Deep-water corals grow slowly, so recovery takes much longer than in shallow waters where nutrients and food-providing zooxanthellae are far more abundant.
In a study during 2001 to 2003, a study of a reef of Lophelia pertusa in the Atlantic off Canada found that the corals were often broken in unnatural ways. And the ocean floor displayed scars and overturned boulders from trawling.
In addition to these managed pressures, deep water coral reefs are also vulnerable to unmanaged pressures (e.g. ocean acidification) and in order to protect these habitats in the long-term methods which assess the relative risks of different pressures are being promoted.
Bottom trawling and natural causes like bioerosion and episodic die-offs have reduced much of Florida's Oculina Banks to rubble, drastically reducing a once-substantial fishery by destroying spawning grounds.
In 1980, Harbor Branch Oceanographic Institution scientists called for protective measures. In 1984, the South Atlantic Fishery Management Council (SAFMC) designated a 315 square kilometres (122 sq mi) area as a Habitat Area of Particular Concern. In 1994, an area called the Experimental Oculina Research Reserve was completely closed to bottom fishing. In 1996, the SAFMC prohibited 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 1,029 square kilometres (397 sq mi). Scientists recently deployed concrete reef balls in an attempt to provide habitat for fish and coral.
Scientists estimate that trawling has damaged or destroyed 30 to 50 percent of the Norwegian shelf coral area. 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.
In 1999, the Norwegian Ministry of Fisheries closed an area of 1,000 square kilometres (390 sq mi) containing the large Sula Reef to bottom trawling. In 2000, an additional area closed, covering about 600 square kilometres (230 sq mi). An area of about 300 square kilometres (120 sq mi) enclosing the Røst Reef, closed in 2002.
Bamboo coral, family Isididae, is a family of mostly deep-sea coral of the phylum Cnidaria. It is a commonly recognized inhabitant of the deep sea, due to the clearly articulated skeletons of the species. Deep water coral species such as this are especially affected by the practice of bottom trawling. These organisms may be an important environmental indicator in the study of long term climate change, as some specimens of bamboo coral have been discovered that are 4,000 years old.Cerevisterol
Cerevisterol (5α-ergosta-7,22-diene-3β,5,6β-triol) is a sterol. Originally described in the 1930s from the yeast Saccharomyces cerevisiae, it has since been found in several other fungi and, recently, in deep water coral. Cerevisterol has some in vitro bioactive properties, including cytotoxicity to some mammalian cell lines.Coral dermatitis
Coral dermatitis is a cutaneous condition caused by injury from the exoskeleton of certain corals.Coral rag
Coral rag is a rubbly limestone composed of ancient coral reef material. The term also refers to the building blocks quarried from these strata, which are an important local building material in areas such as the coast of East Africa and the southeastern United States littoral (e.g. Florida, Bermuda).
It is also the name of a member — the Coral Rag Member — of the Upper Oxfordian Coralline Oolite Formation of North Yorkshire, England.Coral sand
Coral sand is a collection of sand of particles originating in tropical and sub-tropical marine environments from bioerosion of limestone skeletal material of marine organisms. One example of this process is that of parrot fishes which bite off pieces of coral, digest the living tissue, and excrete the inorganic component as silt and sand. However, the term "coral" in coral sand is used loosely in this sense to mean limestone of recent biological origin; corals are not the dominant contributors of sand particles to most such deposits. Rather, remnant skeletal fragments of foraminifera, calcareous algae, molluscs, and crustaceans can predominate. Because it is composed of limestone, coral sand is acid-soluble.Coralliophilinae
Coralliophilinae is a taxonomic group, a subfamily of about 200–250 sea snails, marine gastropod mollusks commonly known as the coral snails or coral shells. This is a subfamily within the very large family Muricidae, the murex or rock snails.
According to the taxonomy of the Gastropoda (Bouchet & Rocroi, 2005), this group is considered to be a subfamily, the Coralliophilinae, of the family Muricidae. Prior to the taxonomy of the Gastropoda (Bouchet & Rocroi, 2005), the Coralliophilinae was recognized as a distinct family the Coralliophilidae. The subfamily Coralliophilinae is monophyletic, as confirmed by genetic research with molecular markers.Darwin Mounds
Darwin Mounds is a large field of undersea sand mounds situated off the north west coast of Scotland that were first discovered in May 1998. They provide a unique habitat for ancient deep water coral reefs and were found using remote sensing techniques during surveys funded by the oil industry and steered by the joint industry and United Kingdom government group the Atlantic Frontier Environment Network (AFEN) (Masson and Jacobs 1998). The mounds were named after the research vessel, itself named for the eminent naturalist and evolutionary theorist Charles Darwin.
The mounds are about 1,000 metres (3,300 ft) below the surface of the North Atlantic ocean, approximately 100 nautical miles (190 km) north-west of Cape Wrath, the north-west tip of mainland Scotland. There are hundreds of mounds in the field, which in total cover approximately 100 square kilometres (39 sq mi). Individual mounds are typically circular, up to 5 metres (16 ft) high and 100 metres (330 ft) wide. Most of the mounds are also distinguished by the presence of an additional feature referred to as a 'tail'. The tails are of a variable extent and may merge with others, but are generally a teardrop shape and are orientated south-west of the mound. The mound-tail feature of the Darwin Mounds is apparently unique globally.Eumunida picta
Eumunida picta is a species of squat lobster found in the deep sea. The species is strongly associated with reefs of Lophelia pertusa, a deep-water coral, and with methane seeps. It is abundant in the western Atlantic Ocean, where it is found from Massachusetts to Colombia.Gulf of Alaska
The Gulf of Alaska (French: Golfe d'Alaska) is an arm of the Pacific Ocean defined by the curve of the southern coast of Alaska, stretching from the Alaska Peninsula and Kodiak Island in the west to the Alexander Archipelago in the east, where Glacier Bay and the Inside Passage are found.
The Gulf shoreline is a rugged combination of forest, mountain and a number of tidewater glaciers. Alaska's largest glaciers, the Malaspina Glacier and Bering Glacier, spill out onto the coastal line along the Gulf of Alaska. The coast is heavily indented with Cook Inlet and Prince William Sound, the two largest connected bodies of water. It includes Yakutat Bay and Cross Sound. Lituya Bay (a fijord north of Cross Sound, and south of Mount Fairweather) is the site of the largest recorded tsunami in history. It serves as a sheltered anchorage for fishing boats.Ivory bush coral
Oculina varicosa, or the ivory bush coral, is a scleractinian deep-water coral primarily found at depths of 70-100m, and ranges from Bermuda and Cape Hatteras to the Gulf of Mexico and the Caribbean. Oculina varicosa flourishes at the Oculina Bank off the east coast of Florida, where coral thickets house a variety of marine organisms. The U.S. National Marine Fisheries Service considers Oculina a genus of concern, due to the threat of rapid ocean warming. Species of concern are those species about which the U.S. Government’s National Oceanic and Atmospheric Administration (NOAA), National Marine Fisheries Service, has some concerns regarding status and threats, but for which insufficient information is available to indicate a need to list the species under the U.S. Endangered Species Act (ESA). While Oculina is considered a more robust genus in comparison to tropical corals, rising ocean temperatures continue to threaten coral health across the planet.List of reefs
This is an incomplete list of notable reefs.Mesophotic coral reef
A Mesophotic coral reef, from meso meaning middle and photic meaning light, is characterised by the presence of both light dependent coral and algae, and organisms that can be found in water with low light penetration. They normally grow between 30 to 40 metres (130 ft) and up to 150 metres (490 ft) in tropical and subtropical water. The most common species at the mesophotic level are corals, sponges and algae. The corals ranges can overlap with Deep-water coral but are distinguished by the presence of zooxanthellae and their requirement for light. They can also be thought of as part of shallow water coral ecosystems, and a crossover of coral species between the two is common. It is thought that these corals could be used as sources for reseeding shallow water coral species. The oldest known mesophotic coral ecosystems have been described from the Silurian of Sweden, such ecosystems are also known from Devonian . Oldest scleractinian-dominated mesophotic ecosystems are known from the TriassicMichael C. Barnette
Michael C. Barnette is an accomplished diver, author, photographer and founder of the Association of Underwater Explorers.Paromola cuvieri
Paromola cuvieri is a species of crab in the family Homolidae, the carrier crabs. It occurs in the eastern Atlantic Ocean and the Mediterranean Sea, from Angola to Norway, the Northern Isles and Iceland. It is demersal, occurring at depths of 10–1,212 metres (33–3,976 ft), but it is primarily found deeper than 80 m (260 ft). It prefers areas with mud and emerging rocks, and has been observed in deep-water coral gardens and sponge aggregations. It is locally common.This reddish crab is sexually dimorphic; the males have larger claws and are overall larger than the females. The carapace of the largest males can reach 21.5 cm (8.5 in), while their claws can span 1.2 m (4 ft). Like other members of the family, most P. cuvieri in their natural habitat carry an object, typically a living sessile invertebrate such as a sponge or deep-water coral, over the carapace in the small hindlegs. This may be used as camouflage, but is also used actively in defense by positioning the object between the crab and a would-be attacker. P. cuvieri is a scavenger of a wide range of animal matters, and a predator of animals such as decapods, but only rarely takes small benthic species (glycerids, cumaceans and amphipods).Particle (ecology)
In marine and freshwater ecology, a particle is a small object. Particles can remain in suspension in the ocean or freshwater. However, they eventually settle (rate determined by Stokes' law) and accumulate as sediment. Some can enter the atmosphere through wave action where they can act as cloud condensation nuclei (CCN). Many organisms filter particles out of the water with unique filtration mechanisms (filter feeders). Particles are often associated with high loads of toxins which attach to the surface. As these toxins are passed up the food chain they accumulate in fatty tissue and become increasingly concentrated in predators (see bioaccumulation). Very little is known about the dynamics of particles, especially when they are re-suspended by dredging. They can remain floating in the water and drift over long distances. The decomposition of some particles by bacteria consumes a lot of oxygen and can cause the water to become hypoxic.Project AWARE
Project AWARE is a registered nonprofit organization working with volunteer scuba divers. With offices in UK, US, and Australia, Project AWARE supports divers acting in their own communities to protect the ocean, with a focus on implementing lasting change in two core areas: shark conservation and marine litter.Reef knoll
A reef knoll is a land-based landform that comprises an immense pile of calcareous material that accumulated on a previously existing ancient sea floor. At the time of its accumulation it may have had enough structure from organisms such as sponges to have been free-standing and to withstand the sea currents as material accumulated, and was likely an atoll. Another possibility is the remains of deep water coral. Such structures are thus often fossil-rich.Røst Reef
The Røst Reef (Norwegian: Røstrevet) is a deep-water coral reef off the coast of the Lofoten islands in Nordland county, Norway. The reef was discovered in 2002, about 100 kilometres (62 mi) west of the island of Røstlandet. It extends over a length of about 43 kilometers (27 mi), and has a width of up to 6.9 kilometers (4.3 mi). The reef is generated by the coral Lophelia pertusa, and is the world's largest known Lophelia reef. It is also the world's largest known deep-water coral reef. The authorities have introduced regulations to protect the reef against trawling. The temperature of the waters near the bottom of the Rost coral reef is 2 °C. WWF recognises the Røst Reef as a global natural heritage that merits protection through Marine Protected Area (MPA) status.Sula Reef
The Sula Reef (Norwegian: Sularevet) is a deep-water coral reef off the coast of Trøndelag, Norway. It is located on the Sula Ridge, named after the island of Sula. The reef is generated by the coral Lophelia pertusa. It has a length of about 13 kilometers (8.1 mi), and is 700 meters (2,300 ft) wide. The thickness of the reef is up to 35 meters (115 ft). Until the discovery of the Røst Reef in 2002, the Sula Reef was the world's largest known Lophelia reef. The Sula Reef is closed to trawling.