Black coral

Antipatharians, also known as black corals or thorn corals, are an order of soft deep-water corals. These corals can be recognized by their jet-black or dark brown chitin skeletons, surrounded by the polyps (the part of coral that is alive).[2] Antipatharians are a cosmopolitan species, existing at nearly every location and depth. However, they are most frequently found on continental slopes under 50 m (164.0 ft) deep.[3] Similar to other corals, it reproduces both sexually and asexually throughout its lifetime. It also provides a miniature ecosystem for other animals to live in.

Black coral
Black coral colony
Scientific classification
Kingdom: Animalia
Phylum: Cnidaria
Class: Anthozoa
Subclass: Hexacorallia
Order: Antipatharia
Milne-Edwards & Haime, 1857

Black corals were originally classified in the subclass Ceriantipatharia along with the ceriantharians,[4] but were later reclassified under Hexacorallia.[5] Though it has historically been used by Pacific Islanders as a medical treatment and in rituals, its only current use is making jewelry.[2][6] Black corals have been declining in numbers and are expected to continue due to the effects of poaching, ocean acidification and climate change.[7]

Classification and taxonomy

Black corals have historically been difficult to classify due to poor-quality specimens. Similar to other corals, they also have few distinguishing morphological characteristics, and the few that there are vary across species. When black corals were first documented by Henri Milne-Edwards and Jules Haime, two French zoologists, they placed all species of antipatharia in the family Antipathidae.[8] In 2015, Dennis Opresko and Tina Molodtsova helped to implement the current taxonomic system.[8]

Blacks corals are classified in the order antipatharia with 7 families, 44 genera, and 280 distinct species.[5] The families are Antipathidae, Aphanipathidae, Cladopathidae, Leiopathidae, Myriopathidae, Schizopathidae, and Stylopathidae.[3] 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 a chitin skeleton, small or medium-sized polyps, and small spines along the skeleton.[9]

The root of the word antipatharia, antipathes, is the Ancient Greek word for "against disease" (named for their use in medicine). In the Hawaiian language, black coral is called ʻēkaha kū moana ("hard bush growing in the sea") and is the official state gem of Hawaii.[10]


List of genera according to the World Register of Marine Species:[11]

  • Family Antipathidae Ehrenberg, 1834
  • Family Aphanipathidae Opresko, 2004
    • subfamily Acanthopathinae Opresko, 2004
    • subfamily Aphanipathinae Opresko, 2004
      • Aphanipathes Brook, 1889
      • Asteriopathes Opresko, 2004
      • Phanopathes Opresko, 2004
      • Pteridopathes Opresko, 2004
      • Tetrapathes Opresko, 2004
  • Family Cladopathidae Kinoshita, 1910
    • subfamily Cladopathinae Kinoshita, 1910
      • Chrysopathes Opresko, 2003
      • Cladopathes Brook, 1889
      • Trissopathes Opresko, 2003
    • subfamily Hexapathinae Opresko, 2003
      • Heteropathes Opresko, 2011
      • Hexapathes Kinoshita, 1910
    • subfamily Sibopathinae Opresko, 2003
      • Sibopathes Van Pesch, 1914
  • Family Leiopathidae Haeckel, 1896
  • Family Myriopathidae Opresko, 2001
    • Antipathella Brook, 1889
    • Cupressopathes Opresko, 2001
    • Myriopathes Opresko, 2001
    • Plumapathes Opresko, 2001
    • Tanacetipathes Opresko, 2001
  • Family Schizopathidae Brook, 1889
    • Abyssopathes Opresko, 2002
    • Alternatipathes Molodtsova & Opresko, 2017
    • Bathypathes Brook, 1889
    • Dendrobathypathes Opresko, 2002
    • Dendropathes Opresko, 2005
    • Lillipathes Opresko, 2002
    • Parantipathes Brook, 1889
    • Saropathes Opresko, 2002
    • Schizopathes Brook, 1889
    • Stauropathes Opresko, 2002
    • Taxipathes Brook, 1889
    • Telopathes MacIsaac & Best, 2013
    • Umbellapathes Opresko, 2005
  • Family Stylopathidae Opresko, 2006
    • Stylopathes Opresko, 2006
    • Triadopathes Opresko, 2006
    • Tylopathes Brook, 1889


Despite its name, black coral is rarely black, and depending on the species it can be white, red, green, yellow, or brown. Black corals get their name from their black skeletons, which are composed primarily of protein and chitin.[12] The corals grow in many unique tree-like patterns, including fan, feather, and whip shapes ranging in height from 10 centimeters to 3 meters, though polyps can be as small as 1 millimeter in size.[8][13] The name 'thorn coral' comes from the tiny spikes that are visible on the skeletons of most black corals.[8] These spikes are roughly 0.5 mm in size, with a triangular shape that can vary widely.[5] A layer of "bark" will form around the coral skeleton as it grows. The polyps that live inside of this bark are small and gelatinous and have six tentacles (unlike most other corals which have eight).[14]

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



Black corals are found in all oceans and across all depth gradients, though they are most prevalent in tropical and subtropical climates. The sole oceanic area in which antiptharians have not been found are brackish waters, though they can inhabit areas with decreased salinity.[9] Despite this wide habitation zone, over 75% of black corals are only capable of survival in depths below 50 meters. Black corals will sometimes help to build reefs, but will more often choose to live alone.[9] Most black corals require a hard surface to attach to, though some can grow in soft mud or sediment. They will also frequently grow where undersea currents flow, which allows them to feed on the meiofauna (organisms smaller than macrofauna but smaller than microfauna) that is swept by. Since undersea currents benefit the corals, they will often grow on or by geographic structures that cause currents, such as continental slopes, cliffs, of undersea plateaus.[9] Black corals are found mostly in low-light waters, due to a lack of free-floating sediment. Corals are frequently found both deep in the water and under geologic formations that block light, such as caves and crevices.[9]


Antipatharians are carnivorous, with the coral's polyps allowing it to feed mostly on meiofauna such as zooplankton.[2][8] The polyps of cnidarians have an oral disk in their center surrounded by the tentacles, which stings and digests food.[9] The reason many corals are fan-shaped is to catch meiofauna. Many corals have also adapted to have polyps on only the downstream side of the coral,[2] allowing them to catch nearly the same amount of animals without wasting energy keeping unnecessary polyps alive.


Vertebrate predation is not a major threat to black corals. Though there are occasional reports of fish such as the parrotfish and butterflyfish gnawing and eating at the polyps of black corals, these reports are rare and even if a single polyp is gnawed off, it will not affect the coral. The skeleton of black coral is hard and inert, due to its composition of protein and chitin, making it nearly inedible. Though there have been reports of black coral skeletons being removed from the stomachs of green sea turtles and sharks, the infrequent nature of these reports leads to the conclusion that black coral is not eaten by any vertebrates.[9]

Invertebrates, such as muricids and ovulids feed on black corals and similar corals regularly. These molluscs may mimic the polyps that the coral typically feeds on, and the eat the tissue. Various molluscs, such as Corraliophila kaofitorum and Phenacovolva carneptica live solely where various species of antipatharia are found, suggesting that they prey on the species.

Life cycle and reproduction

Due to the slow life cycle and deep-water habitats of black coral, little is known about its life cycle and reproduction.[3] Similar to other cnidarians, the life cycle of these corals involves asexual as well as sexual reproduction. Asexual reproduction (also known as budding), is the first method of reproduction used by a black coral during its lifespan.[2] Once a polyp is anchored, it builds a colony by creating a skeleton, growing new branches and making it thicker, similar to the growth of a tree. This method of growing creates "growth rings" which can be used to estimate the age of a colony. Asexual reproduction will also occur if a branch breaks off and a replacement is needed.[2] Though light is not required for growth or development, mature colonies will grow towards light.[15]

Compared to what we know about asexual reproduction, we know little about sexual reproduction in these corals. What we do know is that sexual reproduction 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.[2] 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, which will eventually form a colony.[2] In areas with ideal conditions, antipatharia colonies can grow to be quite dense, creating beds.[9] In some black corals that have been closely examined, colonies will grow roughly 6.4 centimeters (2.5 in) every year. Sexual reproduction occurs after 10 to 12 years; the colony will then reproduce annually for the rest of its life. A large 1.8 meter (6 ft) tall coral tree is somewhere between 30 and 40 years old. The estimated natural lifespan of a antipatharia colony in the epipelagic zone is 70 years. However, in March 2009, scientists released the results of their research on deep-sea (depths of ~300 to 3,000 m) corals throughout the world. They discovered specimens of Leiopathes glaberrima to be among the oldest living organisms on the planet: around 4,265 years old. They show that the "that individual colony longevities are on the order of thousands of years".[16][17] They will also occasionally grow too large to support their own weight, and collapse.[9]

Black corals around the world provide a unique environment for crustaceans, bivalves, and fish. When forty taxa living around black coral beds were surveyed, nearly 60% passed through the bed at some time. 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 was also observed to be common.[18][19][20]

Human use and harvesting

Antipatharians have historically been associated with mystical powers and medicinal properties in Indonesian, Chinese, an Hawaiian culture.[9][21] More recent harvesting has been for use as jewelry.[21][22] Many Indo-Pacific people believed that black coral has curative and anti-evil powers. However, black coral is not ideal for jewelry-making due to it being a soft coral as opposed to a stony coral.[8] This causes jewelry made with it to dry out and break.[8] It can be determined if a sample is true black coral or not by boiling it in milk. This will cause true black coral to emit a faint smell of myrrh.[6]

The best studied and regulated black coral fisheries are in Hawaii, where harvesting has been conducted since the 1960s.[21][23] In the Caribbean harvesting is typically conducted to produce jewelry for sale to tourists, and has followed a boom-and-bust cycle, where new antipatharian populations are discovered and overexploited leading to rapid declines.[21] For example, Cozumel, Mexico, was famed for dense anipatharia beds that have been harvested since the 1960s[24] leading to widespread black coral population declines.[25] Despite better management in Cozumel, including no harvesting permits issued since the mid-1990s, the black coral population had failed to recover when assessed in 2016.[26] Though it is still possible to buy it, black coral is listed in Appendix II of the Convention on International Trade in Endangered Species (CITES).[27][28]


Though Antipatharians are not listed on the IUCN endangered species scale, 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.[29] Particularly on tropical islands and Madagascar, the market for illegally-harvested black corals is large.[29][30] Due to overfishing of mature corals, in some areas nearly 90% of corals are juveniles (under 50 cm (19.7 in) tall.)[31]

Global warming is the primary global threat to antipatharians, as well as all other corals.[7] Though black coral 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.[32] Invasive species such as Carijoa riisei, which were introduced to Hawaiian waters by humans, also pose a significant threat to black corals.[30]


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