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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
Abyss may refer to:
* Abyss (religion), a bottomless pit, or a passage to the underworld
Film and television
* ''The Abyss'' (1910 film), a Danish silent film starring Asta Nielsen
* ''The Abyss'' (1988 film) (''L'Œuvre au noir''), a French- ...
, beyond where water temperatures may be as cold as . Deep-water corals belong to the
Phylum Cnidaria and are most often
stony corals
Scleractinia, also called stony corals or hard corals, are marine animals in the phylum Cnidaria that build themselves a hard skeleton. The individual animals are known as polyps and have a cylindrical body crowned by an oral disc in which a mo ...
, but also include
black and thorny 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
Zooxanthellae is a colloquial term for single-celled dinoflagellates that are able to live in symbiosis with diverse marine invertebrates including demosponges, corals, jellyfish, and nudibranchs. Most known zooxanthellae are in the genus ''Sy ...
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,
bioherm
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 ...
s, 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 cable
A submarine communications cable is a cable laid on the sea bed between land-based stations to carry telecommunication signals across stretches of ocean and sea. The first submarine communications cables laid beginning in the 1850s carried tel ...
s and fishing methods such as bottom trawling
Bottom trawling is trawling (towing a trawl, which is a fishing net) along the seafloor. It is also referred to as "dragging". The scientific community divides bottom trawling into benthic trawling and demersal trawling. Benthic trawling is towin ...
tend to break corals apart and destroy reefs. The deep-water habitat is designated as a United Kingdom Biodiversity Action Plan
The United Kingdom Biodiversity Action Plan or (UK BAP) was the UK government's response to the Convention on Biological Diversity, opened for signature at the Rio Earth Summit in 1992. The UK was the first country to produce a national Biodiversi ...
habitat.
Discovery and study
Deep-water corals are enigmatic because they construct their reefs in deep, dark, cool waters at high latitudes, such as Norway's Continental Shelf
A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an island ...
. 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
Porcupine Bank is an area of the Irish shelf, on the fringes of the Atlantic Ocean approximately west of Ireland. The relatively raised area of seabed, 200 m below sea level at its highest, lies between the deep-water Porcupine Seabight and Rock ...
, off Ireland. The first ever live video of a large deep-water coral reef was obtained in July, 1982, when Statoil
Equinor ASA (formerly Statoil and StatoilHydro) is a Norwegian state owned enterprise, state-owned multinational energy company headquartered in Stavanger. It is primarily a petroleum company, petroleum company, operating in 36 countries with ad ...
surveyed a tall and wide reef perched at water depth near Fugløy Island, north of the Polar Circle
A polar circle is a geographic term for a conditional circular line (arc) referring either to the Arctic Circle or the Antarctic Circle. These are two of the keynote circles of latitude (parallels). On Earth, the Arctic Circle is currently ...
, 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
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Eart ...
), several scientists hypothesize that there may be a link between the existence of the deep-water coral reefs and nutrients seepage (light hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ex ...
s, such as methane, ethane
Ethane ( , ) is an organic chemical compound with chemical formula . At standard temperature and pressure, ethane is a colorless, odorless gas. Like many hydrocarbons, ethane is isolated on an industrial scale from natural gas and as a petr ...
, and propane
Propane () is a three-carbon alkane with the molecular formula . It is a gas at standard temperature and pressure, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used a ...
) through the seafloor. This hypothesis is called the 'hydraulic theory' for deep-water coral reefs.
Lophelia communities support diverse marine life, such as sponge
Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through t ...
s, polychaete worm
Polychaeta () is a paraphyletic class of generally marine annelid worms, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are mad ...
s, mollusk
Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is e ...
s, crustacean
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...
s, brittle star
Brittle stars, serpent stars, or ophiuroids (; ; referring to the serpent-like arms of the brittle star) are echinoderms in the class Ophiuroidea, closely related to starfish. They crawl across the sea floor using their flexible arms for locomo ...
s, starfish
Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea (). Common usage frequently finds these names being also applied to ophiuroids, which are correctly referred to as brittle stars or basket stars. Starfish ...
, sea urchin
Sea urchins () are spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin live on the seabed of every ocean and inhabit every depth zone from the intertidal seashore down to . The spherical, hard shells (tests) of ...
s, bryozoans, sea spider
Sea spiders are marine arthropods of the order Pantopoda ( ‘all feet’), belonging to the class Pycnogonida, hence they are also called pycnogonids (; named after ''Pycnogonum'', the type genus; with the suffix '). They are cosmopolitan, fou ...
s, fish, and many other vertebrate and invertebrate species.[
The first international symposium for deep-water corals took place in ]Halifax, Canada
Halifax is the capital and largest municipality of the Canadian province of Nova Scotia, and the largest municipality in Atlantic Canada. As of the 2021 Census, the municipal population was 439,819, with 348,634 people in its urban area. The ...
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 and saw giant coral forests, darting schools of fish, and a seafloor carpeted in brittle star
Brittle stars, serpent stars, or ophiuroids (; ; referring to the serpent-like arms of the brittle star) are echinoderms in the class Ophiuroidea, closely related to starfish. They crawl across the sea floor using their flexible arms for locomo ...
s. During this expedition, scientists identified 16 species of corals. This research 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.
Taxonomy
Corals are animal
Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...
s in the phylum
In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature f ...
Cnidaria
Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter.
Their distinguishing feature is cnidocytes, specialized cells that th ...
and the class Anthozoa
Anthozoa is a subphylum of marine invertebrates which includes the sea anemones, Scleractinia, stony corals and Alcyonacea, soft corals. Adult anthozoans are almost all attached to the seabed, while their larvae can disperse as part of the plank ...
. Anthozoa is broken down into two subclasses Octocorals
Octocorallia (also known as Alcyonaria) is a class of Anthozoa comprising around 3,000 species of water-based organisms formed of colonial polyps with 8-fold symmetry. It includes the blue coral, soft corals, sea pens, and gorgonians (sea fans ...
(Alcyonaria) and Hexacorals (Zoantharia). Octocorals are soft corals such as sea pen
Sea pens are colonial marine cnidarians belonging to the order Pennatulacea. There are 14 families within the order; 35 extant genera, and it is estimated that of 450 described species, around 200 are valid. Sea pens have a cosmo ...
s. Hexacorals include sea anemones and hard bodied corals. Octocorals contain eight body extensions while Hexacorals have six. Most deep-water corals are stony corals.
Distribution
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 areas with warmer water such as along the Florida coast. In the north Atlantic, the principal coral species that contribute to reef formation are ''Lophelia pertusa
''Lophelia pertusa'', the only species in the genus ''Lophelia'', is a cold-water coral that grows in the deep waters throughout the North Atlantic ocean, as well as parts of the Caribbean Sea and Alboran Sea. Although ''L. pertusa'' reefs are ...
'', ''Oculina varicosa
''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 ...
'', ''Madrepora oculata
''Madrepora oculata'', also called zigzag coral, is a Scleractinia, stony coral that is found worldwide outside of the polar regions, growing in deep water coral, deep water at depths of 80–1500 meters. It was first described by Carl Linnaeus i ...
'', ''Desmophyllum
''Desmophyllum'' is a genus of cnidarians belonging to the family Caryophylliidae
The Caryophylliidae are a family of stony corals found from the tropics to temperate seas, and from shallow to very deep water.
Genera
*'' Africana'' Ocana & ...
cristagalli'', ''Enallopsammia
''Enallopsammia'' is a genus of cnidarians belonging to the family Dendrophylliidae.
The genus has cosmopolitan distribution.
Species:
*''Enallopsammia profunda''
*''Enallopsammia pusilla''
*''Enallopsammia reflexa''
*''Enallopsammia rostrat ...
rostrata'', '' Solenosmilia variabilis'', and ''Goniocorella
''Goniocorella'' is a genus of cnidarians belonging to the family Caryophylliidae
The Caryophylliidae are a family of stony corals found from the tropics to temperate seas, and from shallow to very deep water.
Genera
*'' Africana'' Ocana & ...
dumosa''. Four genera (''Lophelia'', ''Desmophyllum'', ''Solenosmilia'', and ''Goniocorella'') constitute most deep-water coral banks at depths of .
''Madrepora oculata'' occurs as deep as 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 in the Straits of Florida (Cairns and Stanley, 1982).
''Lophelia pertusa'' distribution
One of the most common species, ''Lophelia pertusa
''Lophelia pertusa'', the only species in the genus ''Lophelia'', is a cold-water coral that grows in the deep waters throughout the North Atlantic ocean, as well as parts of the Caribbean Sea and Alboran Sea. Although ''L. pertusa'' reefs are ...
'', lives in the Northeast and Northwest Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...
, Brazil
Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
and off Africa
Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
’s west coast.
In addition to ocean bottoms, scientists find ''Lophelia'' colonies on North Sea oil
North Sea oil is a mixture of hydrocarbons, comprising liquid petroleum and natural gas, produced from petroleum reservoirs beneath the North Sea.
In the petroleum industry, the term "North Sea" often includes areas such as the Norwegian Sea and ...
installations, although oil and gas production may introduce noxious substances into the local environment.
The world's largest known deep-water ''Lophelia'' coral complex is the Røst Reef
The Rost Reef ( no, 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 west of the island of Røstlandet. It extends over a length of about , and has a wi ...
. It lies between deep, west of Røst
Røst is a small island municipality in Nordland county, Norway. It is part of the traditional district of Lofoten. The administrative centre of the municipality is the village of Røstlandet on the island of Røstlandet.
The island municipa ...
island in the Lofoten
Lofoten () is an archipelago and a traditional district in the county of Nordland, Norway. Lofoten has distinctive scenery with dramatic mountains and peaks, open sea and sheltered bays, beaches and untouched lands. There are two towns, Svolvær ...
archipelago, in Norway, inside the Arctic Circle. Discovered during a routine survey in May 2002, the reef is still largely intact. It is approximately long by wide.
Some further south is the Sula Reef, located on the Sula Ridge, west of Trondheim
Trondheim ( , , ; sma, Tråante), historically Kaupangen, Nidaros and Trondhjem (), is a city and municipality in Trøndelag county, Norway. As of 2020, it had a population of 205,332, was the third most populous municipality in Norway, and ...
on the mid-Norwegian Shelf, at . It is long, wide, and up to high, an area one-tenth the size of the Røst Reef.
Discovered and mapped in 2002, Norway's Tisler Reef lies in the Skagerrak
The Skagerrak (, , ) is a strait running between the Jutland peninsula of Denmark, the southeast coast of Norway and the west coast of Sweden, connecting the North Sea and the Kattegat sea area through the Danish Straits to the Baltic Sea.
The ...
on the submarine border between Norway and Sweden
Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic country located on ...
at a depth of and covers an area of . 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
The Faroe Islands ( ), or simply the Faroes ( fo, Føroyar ; da, Færøerne ), are a North Atlantic island group and an autonomous territory of the Kingdom of Denmark.
They are located north-northwest of Scotland, and about halfway bet ...
, an island group between the Norwegian Sea
The Norwegian Sea ( no, Norskehavet; is, Noregshaf; fo, Norskahavið) is a marginal sea, grouped with either the Atlantic Ocean or the Arctic Ocean, northwest of Norway between the North Sea and the Greenland Sea, adjoining the Barents Sea to ...
and the Northeast Atlantic Ocean. At depths from , ''L. pertusa'' is chiefly on the Rockall Bank
Rockall () is an uninhabitable granite islet situated in the North Atlantic Ocean. The United Kingdom claims that Rockall lies within its exclusive economic zone (EEZ) and is part of its territory, but this claim is not recognised by Ireland. ...
and on the shelf break north and west of Scotland.
The Porcupine Seabight
The Porcupine Seabight or Porcupine Basin is a deep-water oceanic basin located on the continental margin in the northeastern portion of the Atlantic Ocean. It can be found in the southwestern offshore portion of Ireland and is part of a series o ...
, the southern end of the Rockall Bank
Rockall () is an uninhabitable granite islet situated in the North Atlantic Ocean. The United Kingdom claims that Rockall lies within its exclusive economic zone (EEZ) and is part of its territory, but this claim is not recognised by Ireland. ...
, and the shelf to the northwest of Donegal Donegal may refer to:
County Donegal, Ireland
* County Donegal, a county in the Republic of Ireland, part of the province of Ulster
* Donegal (town), a town in County Donegal in Ulster, Ireland
* Donegal Bay, an inlet in the northwest of Ireland b ...
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 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 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.[
]
Darwin Mounds
Among the most researched deep-water coral areas in the United Kingdom
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
are the 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 tech ...
. Atlantic Frontier Environmental Network (AFEN) discovered them in 1998 while conducting large-scale regional sea floor surveys north of Scotland
Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to the ...
. They discovered two areas of hundreds of sand and deep-water coral mounds at depths of about in the northeast corner of the Rockall Trough
The Rockall Trough ( gd, Clais Sgeir Rocail) is a deep-water bathymetric feature to the northwest of Scotland and Ireland, running roughly from southwest to northeast, flanked on the north by the Rockall Plateau and to the south by the Porcupi ...
, approximately 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 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 in diameter and 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
Xenophyophorea is a clade of foraminiferans. Members of this class are multinucleate unicellular organisms found on the ocean floor throughout the world's oceans, at depths of . They are a kind of foraminiferan that extract minerals from their s ...
(''Syringammina fragilissima
''Syringammina'' is a xenophyophore found off the coast of Scotland, near Rockall. It is one of the largest single-celled organisms known, at up to across. It was first described in 1882 by the oceanographer John Murray, after being discovere ...
'') which are giant unicellular organisms that can grow up to 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'' distribution
''Oculina varicosa
''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 ...
'' is a branching ivory coral that forms giant but slow-growing, bushy thickets on pinnacles up to in height. The ''Oculina'' Banks, so named because they consist mostly of ''Oculina varicosa'', exist in 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
Fort Pierce is a city in and the county seat of St. Lucie County, Florida, United States. The city is part of the Treasure Coast region of Atlantic Coast Florida. It is also known as the Sunrise City, sister to San Francisco, California, the Suns ...
to Daytona, Florida
Daytona Beach, or simply Daytona, is a coastal Resort town, resort-city in east-central Florida. Located on the eastern edge of Volusia County, Florida, Volusia County near the East Coast of the United States, Atlantic coastline, its population ...
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
A gag is usually an item or device designed to prevent speech, often as a restraint device to stop the subject from calling for help and keep its wearer silent. This is usually done by blocking the mouth, partially or completely, or attempting ...
, scamp, red grouper
The red grouper (''Epinephelus morio'') is a species of marine ray-finned fish, a grouper from the subfamily Epinephelinae which is part of the Family (biology), family Serranidae, which also includes the Anthiinae, anthias and sea basses. It is ...
, speckled hind, black sea bass
The black sea bass (''Centropristis striata'') is a species of marine ray-finned fish, a sea bass from the subfamily Serraninae which is part of the family Serranidae, which also includes the groupers and anthias. It is found in the western Atl ...
, red porgy
The red porgy (''Pagrus pagrus''), or common seabream, is a species of marine ray-finned fish in the family Sparidae. It is found in shallow waters on either side of the Atlantic Ocean, being present on the western coast of Europe and the Mediter ...
, rock shrimp, and calico scallop
Calico (; in British usage since 1505) is a heavy plain weave, plain-woven textile made from unbleached, and often not fully processed, cotton. It may also contain unseparated husk parts. The fabric is far coarser than muslin, but less coarse an ...
.
Growth and reproduction
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
Bathymetry (; ) is the study of underwater depth of ocean floors (''seabed topography''), lake floors, or river floors. In other words, bathymetry is the underwater equivalent to hypsometry or topography. The first recorded evidence of water de ...
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
Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...
and rely on ocean currents
An ocean current is a continuous, directed movement of sea water generated by a number of forces acting upon the water, including wind, the Coriolis effect, breaking waves, cabbeling, and temperature and salinity differences. Depth contours, s ...
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 per year. By contrast, branching shallow-water corals, such as ''Acropora
''Acropora'' is a genus of small polyp stony coral in the phylum Cnidaria. Some of its species are known as table coral, elkhorn coral, and staghorn coral. Over 149 species are described. ''Acropora'' species are some of the major reef corals r ...
'', may exceed 10–20 cm/yr. Reef structure growth estimates are about 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.
Deep-water corals use ]nematocysts
A cnidocyte (also known as a cnidoblast or nematocyte) is an explosive cell containing one large secretory organelle called a cnidocyst (also known as a cnida () or nematocyst) that can deliver a sting to other organisms. The presence of this c ...
on their tentacles to stun prey. Deep-water corals feed on zooplankton
Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...
, crustaceans
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...
and even krill
Krill are small crustaceans of the order Euphausiacea, and are found in all the world's oceans. The name "krill" comes from the Norwegian
Norwegian, Norwayan, or Norsk may refer to:
*Something of, from, or related to Norway, a country in n ...
.
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
''Lophelia pertusa'', the only species in the genus ''Lophelia'', is a cold-water coral that grows in the deep waters throughout the North Atlantic ocean, as well as parts of the Caribbean Sea and Alboran Sea. Although ''L. pertusa'' reefs are ...
'' 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.
Importance
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.
Human impact
The primary human impact on deep-water corals is from deep-water trawling. Trawlers Trawler may refer to:
Boats
* Fishing trawler, used for commercial fishing
* Naval trawler, a converted trawler, or a boat built in that style, used for naval purposes
** Trawlers of the Royal Navy
* Recreational trawler, a pleasure boat built tra ...
drag nets across the ocean floor, disturbing sediments, breaking and destroying deep-water corals. Another harmful method is long line fishing
Longline fishing, or longlining, is a commercial fishing angling technique that uses a long ''main line'' with baited hooks attached at intervals via short branch lines called ''snoods'' or ''gangions''.[Mississippi Canyon
The Mississippi Canyon is an undersea canyon, part of the Mississippi Submarine Valley in the North-central Gulf of Mexico, south of Louisiana. According to the U.S. Geological Survey GLORIA Mapping Program, it is the dominant feature of the nor ...]
in the Gulf of Mexico increased from 4 to 9 percent before the Deepwater Horizon oil spill
The ''Deepwater Horizon'' oil spill (also referred to as the "BP oil spill") was an industrial disaster that began on 20 April 2010 off of the coast of the United States in the Gulf of Mexico on the BP-operated Macondo Prospect, considered ...
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
Ocean acidification is the reduction in the pH value of the Earth’s ocean. Between 1751 and 2021, the average pH value of the ocean surface has decreased from approximately 8.25 to 8.14. The root cause of ocean acidification is carbon dioxid ...
) and in order to protect these habitats in the long-term methods which assess the relative risks of different pressures are being promoted.
Oculina Banks
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
Harbor Branch Oceanographic Institute (HBOI, FAU Harbor Branch) is a non-profit oceanographic institution operated by Florida Atlantic University in Fort Pierce, Florida, United States. Founded in 1971 as non-profit research organization, the i ...
scientists called for protective measures. In 1984, the South Atlantic Fishery Management Council (SAFMC) designated a area as a Habitat Area of Particular Concern. In 1994, an area called the Experimental Oculina Research Reserve
The Experimental Oculina Research Reserve preserves the Oculina Banks, a reef of ivory bush coral (''Oculina varicosa'') off the coast of Fort Pierce, Florida. ''Oculina varicosa'' is a U.S. National Marine Fisheries Service species of concern. Sp ...
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 . Scientists recently deployed concrete reef balls
Reef Ball Foundation, Inc. is a 501(c)(3) non-profit organization that functions as an international environmental non-governmental organization. The foundation uses reef ball artificial reef technology, combined with coral propagation, transpla ...
in an attempt to provide habitat for fish and coral.
Sula and Røst
Scientists estimate that trawling has damaged or destroyed 30 to 50 percent of the Norwegian shelf
The Norwegian continental shelf ( no, Den norske kontinentalsokkelen) (abbreviated as NCS) is the continental shelf over which Norway exercises sovereign rights as defined by the United Nations Convention on the Law of the Sea.
The area of the ...
coral area. The International Council for the Exploration of the Sea
The International Council for the Exploration of the Sea (ICES; french: Conseil International de l'Exploration de la Mer, ''CIEM'') is a regional fishery advisory body and the world's oldest intergovernmental science organization. ICES is headqu ...
, the European Commission
The European Commission (EC) is the executive of the European Union (EU). It operates as a cabinet government, with 27 members of the Commission (informally known as "Commissioners") headed by a President. It includes an administrative body o ...
’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
The Royal Norwegian Ministry of Fisheries and Coastal Affairs ( no, Fiskeri- og kystdepartementet) was a Norwegian ministry responsible for fisheries industry, aquaculture industry, seafood safety, fish health and welfare, harbours, water transport ...
closed an area of containing the large Sula Reef to bottom trawling. In 2000, an additional area closed, covering about . An area of about enclosing the Røst Reef
The Rost Reef ( no, 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 west of the island of Røstlandet. It extends over a length of about , and has a wi ...
, closed in 2002.[
]
Darwin mounds
The European Commission
The European Commission (EC) is the executive of the European Union (EU). It operates as a cabinet government, with 27 members of the Commission (informally known as "Commissioners") headed by a President. It includes an administrative body o ...
introduced an interim trawling ban in the 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 tech ...
area, in August 2003, followed by a permanent closure to bottom trawling in March 2004. The European Commission designated the area as a Site of Community Importance in December 2009, and was designated a Special Area of Conservation by the UK Government in December 2015.
See also
* Coral reef
A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups.
Co ...
* Mesophotic coral reef
A Mesophotic coral reef or mesophotic coral ecosystem (MCE), originally from the Latin word ''meso'' (meaning middle) and ''photic'' (meaning light), is characterised by the presence of both light-dependent coral and algae, and organisms that can b ...
References
*Etnoyer, P. J., Wickes, L. N., Silva, M., Dubick, J. D., Balthis, L., Salgado, E., & Macdonald, I. R. (2015). Decline in condition of gorgonian octocorals on mesophotic reefs in the northern Gulf of Mexico: Before and after the Deepwater Horizon oil spill. Coral Reefs, 35(1), 77-90.
External links
Deep-sea Corals
overview on the Smithsonian Ocean Portal
Lophelia.org, a website devoted to the cold-water coral habitats from Heriot-Watt University in Edinburgh, Scotland
Deep Sea Corals: Out of Sight, But No Longer Out of Mind
report on deep sea corals around the world from Oceana
Deep-sea Corals at the Woods Hole Oceanographic Institution
{{corals, state=expanded
Coral reefs
Anthozoa