Black coral

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Black coral
Black coral colony
Black coral colony
CITES Appendix II (CITES)
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Cnidaria
Subphylum: Anthozoa
Class: Hexacorallia
Order: Antipatharia
Milne-Edwards & Haime, 1857
Families[1]

Antipatharians, also known as black corals or thorn corals,

continental slopes under 50 m (164 ft) deep. A black coral reproduces both sexually and asexually
throughout its lifetime. Many black corals provide housing, shelter, food, and protection for other animals.

Black corals were originally classified in the order

Pacific Islanders for medical treatment and in rituals, its only modern use is making jewelry. Black corals have been declining in numbers and are expected to continue declining due to the effects of poaching, ocean acidification and climate change
.

Etymology

Despite its name, a black coral is rarely black, and depending on the species can be white, red, green, yellow, or brown. The corals derive their name from their black skeletons, which are composed of protein and chitin.[3] Black corals are also known as thorn corals due to the microscopic spines lining their skeletons.[4]

The name Antipatharia comes from the Ancient Greek word antipathes ("against disease"). In the Hawaiian language, a black coral is called ʻēkaha kū moana ("hard bush growing in the sea"); it is the official state gem of Hawaii.[5] In Malay, the corals are called akah bahar ("root of the sea"), likely named for their tendency to grow at low-light depths.[6]

Taxonomy and classification

Black corals have historically been difficult to classify due to poor-quality

phylogenetic study confirmed the new taxonomic system.[7]

Blacks corals are classified in the

Leiopathidae, Myriopathidae, Schizopathidae, and Stylopathidae.[8] Black corals can be distinguished from other corals by their black, flexible skeletons and near-total lack of any kind of protection from sediment. All black corals have small or medium-sized polyps and a chitin skeleton, lined with small spines.[9]

Genera

Leiopathidae
Myriopathes ulex
Myriopathidae
Bathypathes Coral
Schizopathidae
Families of black corals

List of genera according to the World Register of Marine Species:[10]

Physical characteristics

A sample of coral next to its skeleton, showing the minuscule spines all along it

The skeletons of these corals grow in many patterns unique to this order, such as whips, trees, fans, or coils. These range in size from 10 to 300 cm (3.94 to 118 in), though polyps can be as small as 1 mm (0.0394 in) in size.

hermaphroditic.[14]

Unlike the vast majority of other corals, black corals have no protection against abrasive materials such as sand and rocks and lack muscular development which can help the corals to hide. These factors can lead to sediment tearing the soft tissue, resulting in death. In response, corals live near crevices, which allows much of their body to be protected.[9]

Ecology

Habitat

A Cirrhipathes coral, sometimes known as wire coral

Black corals occur throughout all the oceans from the surface down to the deep-sea, though nearly 75% of species are only found at depths below 50 m (164 ft). The sole oceanic area in which black corals have not been found are

continental slopes, cliffs, caves, or undersea plateaus.[9] Species distributions of black corals are poorly understood, and while many deep sea black corals have large distributions, more recent work has indicated that shallow black coral species—such as Antipathes grandis—can be found spanning from the Indian to the Pacific Ocean.[16]

Diet

Black corals are carnivorous, with the coral's polyps allowing it to feed mostly on meiofauna such as

cnidarians have an oral disk in their center which serves as the mouth for the coral. The disk is surrounded by the tentacles, which stings and digests food.[9] The reason many corals are fan-shaped is to catch meiofauna. Many corals only have polyps on the downstream side of the coral,[17] allowing them to catch nearly the same number of animals without wasting energy keeping unnecessary polyps alive.[17]

A princess parrotfish, one of the few predators of black coral

Predators

Vertebrate predation is not a major threat to black corals.[15] There are rare reports of parrotfish and butterflyfish gnawing and eating at the polyps of black corals, but even if a polyp is gnawed off, it will not affect the coral as a whole. The skeleton of a black coral is hard and inert, due to its composition of protein and chitin, making it nearly inedible. Though black coral skeletons have been found in the stomachs of green sea turtles and sharks, these incidents are rare; it has thus been suggested that black corals are not a major part of any vertebrate diets.[9]

However,

mollusks mimic the polyps that the coral typically feeds on and is taken inside of the coral. They will then consume the polyps from the inside out.[9] Various mollusks, such as Coralliophila kaofitorum and Phenacovolva carneptica live solely where various species of black corals are found, suggesting that they prey exclusively on the species.[15]

Interactions

Black corals around the world provide a unique environment for

bivalves, and fish. Some species, such as Dascyllus albisella and Centropyge potteri inhabit specific coral trees. Due to this abundance of species, nighttime predation around the coral beds has been observed.[18][19][20]

Life cycle and reproduction

Due to the slow life cycle and deep-water habitats of black coral, little is known about their life cycle and reproduction.

growth rings" which can be used to estimate the age of a colony.[21] Asexual reproduction can also occur if a branch breaks off and a replacement is needed.[17] Though light is not required for growth or development, mature colonies will grow towards light. Why they do so is unknown.[22]

Antipathes dendrochristos growing several hundred meters down in the ocean

Sexual reproduction in these corals remains largely unstudied. It occurs after the coral colony is established; a colony will produce eggs and sperm, which meet in the water to create larvae that use currents to disperse and settle in new areas.[17] The larval stage of the coral, called a planula, will drift along until it finds a surface on which it can grow. Once it settles, it metamorphoses into its polyp form and creates skeletal material to attach itself to the seafloor. It will then begin to bud, which will create new polyps and eventually form a colony.[17] In areas with ideal conditions, black coral colonies can grow to be extremely dense, creating beds.[9] In some black corals that have been closely examined, colonies will grow roughly 6.4 cm (2.52 in) every year. Sexual reproduction occurs after 10 to 12 years of growth; the colony will then reproduce annually for the rest of its life. The male to female polyp ratio is 1:1, with females producing anywhere from 1.2 million to 16.9 million oocytes.[23] A large 1.8 m (5.91 ft) tall coral tree is somewhere between 30 and 40 years old.[17]

The estimated natural lifespan of a black coral colony in the

epipelagic zone is 70 years. However, in March 2009 around 4,265 years old specimens of Leiopathes glaberrima were found at depths of nearly 300 to 3,000 m (984 to 9,840 ft), making them some of the oldest living organisms on earth. The researchers showed that the "individual colony longevities are on the order of thousands of years."[24][25] Rarely, black corals will grow too large to support their own weight, and collapse.[9]

Human use and harvesting

Black coral bracelet

Black corals have historically been associated with mystical and

stony,[4] causing jewelry made with it to dry out and break.[4] If a real black coral is boiled in milk, it will smell of myrrh; this test can be used to determine if a sample is genuine.[28]

The best studied and regulated black coral fisheries are in Hawaii, where they have been harvested since the 1960s.

boom-and-bust cycle, where new coral populations are discovered and overexploited leading to rapid declines.[26] For example, Cozumel, Mexico, was famed for dense black coral beds that have been harvested since the 1960s[30] leading to widespread black coral population declines.[31] Despite improvements in management in Cozumel, including no harvesting permits issued since the mid-1990s, the black coral population had failed to recover when assessed in 2016.[32] Though it is illegal to move black corals across international borders without authorization, as they are listed in Appendix II of the Convention on International Trade in Endangered Species (CITES), it is still possible to buy them.[33]

Though various methods have been proposed for quicker and more efficient rejuvenation of black coral colonies, none have worked to the point where these corals could be commercially farmed.[34]

Threats

A Bathypathes species growing in a brush shape

Though black corals are not listed on the IUCN Red List, a number of factors threaten them today. The largest single threat is poaching— though the majority of black coral fisheries are heavily regulated, there is still a black market for the corals.[35] Particularly on tropical islands and Madagascar, the market for illegally-harvested black corals is large.[35][36] Due to overfishing of mature corals, in some areas nearly 90% of corals are juveniles (less than 50 cm (19.7 in) tall.)[37]

Global warming is the primary threat to black corals worldwide, as well as all other corals.[38] Though black corals rarely builds reefs (the most threatened areas), threats caused by climate change such as coral bleaching, rising sea temperatures, changing underwater currents, and changing salinity and pH also affect deep-sea corals.[39] Invasive species such as Carijoa riisei, which were introduced to Hawaiian waters by humans, may pose a significant threat to black corals.[36]

References

  1. ^ a b Tina Molodtsova, Dennis Opresko (2020). "Antipatharia". WoRMS. World Register of Marine Species. Retrieved 13 May 2020.
  2. ^ a b c Opresko, Dennis. "Spotlight on Antipatharians (Black Corals)". NMNH. Retrieved 4 May 2020.
  3. ^
    PMID 22546360
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  4. ^ a b c d e f g "Spotlight on antipatharians". NMNH. 18 April 2016. Retrieved 4 September 2019.
  5. ^ Grigg, Richard W. (1993). "Precious Coral Fisheries of Hawaii and the U.S. Pacific Islands" (PDF). Marine Fisheries Review. 55 (2): 54. Retrieved 29 September 2010.
  6. ISBN 1149951974
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  7. PMID 17049278. Retrieved 4 May 2020.{{cite journal}}: CS1 maint: multiple names: authors list (link
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  8. ^ a b NOAA. "Black Corals of Hawaii". oceanexplorer.noaa.gov.
  9. ^ a b c d e f g h i j Wagner, Daniel (December 2011). The biology and ecology of Hawaiian black corals (Cnidaria : Anthozoa: Hexacorallia: Antipatharia) (PhD). University of Hawaii at Manoa.
  10. ^ Dennis Opresko (2019). "Antipatharia". WoRMS. World Register of Marine Species. Retrieved 25 November 2019.
  11. ^ "Black Coral: Hawaii State Gem". State Symbols USA. 21 September 2014. Retrieved 13 September 2019.
  12. ^
    PMID 29314907
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  13. ^ Milne-Edwards and Haine. "Antipatharia sp (Milne-Edwards & Haime, 1857): "Black Coral"". EdwardsLabs. Archived from the original on 30 October 2019. Retrieved 30 October 2019.
  14. ^ Bo, Marzia; Wijgerde, Tim (19 November 2014). "Black corals". Reefs. Retrieved 4 May 2020.
  15. ^
    PMID 22877611
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  16. ISSN 1755-2672
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  17. ^ a b c d e f g h "Black Coral". Waikiki Aquarium. 2013-11-21.
  18. S2CID 41135750
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  19. ISBN 978-0-87850-138-0
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  20. doi:10.3354/meps09228
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  21. ISBN 978-94-010-5428-7. {{cite book}}: |journal= ignored (help
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  22. hdl:10125/4416
    . Retrieved 12 November 2019.
  23. S2CID 85999468
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  24. PMID 19307564
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  25. ^ Graczyk, Michael (25 March 2009). "Scientists ID living coral as 4,265 years old". The Associated Press.
  26. ^
    ISBN 9783319313030
  27. PMID 22877611. {{cite book}}: |journal= ignored (help
    )
  28. doi:10.1038/110217a0
    . Retrieved 28 October 2019.
  29. S2CID 38992352
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  30. ^ Kenyon, J. (1984). "Black coral off Cozumel". Sea Frontiers. 30: 267–272.
  31. ^ Padilla, C., & Lara, M. (2003). Banco Chinchorro: the last shelter for black coral in the Mexican Caribbean. Bulletin of Marine Science, 73(1), 197–202.
  32. PMID 30013832
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  33. ^ "Appendices". CITES. Retrieved 29 October 2019.
  34. S2CID 12598714
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  35. ^ a b Terrana, Lucas; Todinanahary, Gildas Georges Boleslas; Eeckhaut, Igor (24 June 2016). Illegal harvesting and trading of black corals (Antipatharia) in Madagascar: the necessity of field studies. 13th International Coral Reef Symposium.
  36. ^ a b "Case Study for Black Coral from Hawaii" (PDF). CITES. Retrieved 4 November 2019.
  37. doi:10.1080/00288330.1985.9516111
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  38. ^ "How does Climate Change Affect Coral Reefs?". NOAA. Retrieved 28 October 2019.
  39. ^ Guinotte, John (2005). "Climate Change and Deep-sea Corals" (PDF). The Journal of Marine Education. 21 (4). Retrieved 4 November 2019.
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