Antipatharians, also known as Black corals or thorn corals, are an order of soft deep-water corals. Black corals are easily recognized by their shiny, jet-black skeletons, surrounded by the living coral polyps. Black Corals are a cosmopolitan species. They also exist at nearly every depth location. However, they are most common on continental slopes at roughly 30 meters (100 ft) depth. 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 colony|
Milne-Edwards & Haime, 1857
Black corals were originally classified in the taxon Ceriantipatharia along with the ceriantharians, but were later reclassified under Hexacorallia. Though it has historically been used in rituals, its only current use is making jewelry.
Black corals have historically been difficult to classify, due to poor-quality specimens and a lack of clear classification for different genera and species. Also, like many other colonial organisms, they have few morphological characteristics, and the few that there are variable across species. For a time, all species of black coral were placed in the Antipathes family. That, however, changed in 2015, when the current taxonomic system was implemented.
Black corals are a group of 280 species of corals. Those 280 species are divided into seven known families, which are further divided into 45 known genera. The seven distinct families of antipatharians are: Antipathidae, Aphanipathidae, Cladopathidae, Leiopathidae, Myriopathidae, Schizopathidae, and Stylopathidae. These seven families are separated both by their bathypelagic distribution and their morphological characteristics. The families are distinguished by physical characteristics, the most prominent of which are the shape and size of the polyps, the structure of the chitin skeleton, and morphology of the coral's spines. Within the families, the individual genera and species are separated by the growth patterns of the skeleton, the size and shape of the polyps, and the morphology of the spines. In recent years, genetic data has also been used.
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 instead from their black skeletons, which are made of protein and chitin. The corals grow in many unique, tree-like patterns, some of which are 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. The name 'thorn coral' comes from the tiny spikes that are visible on the chitin skeletons of most antipatharians. These spikes are usually .5 mm in size, with a widely varied triangular shape.
A layer of "bark" will have formed around the coral skeleton. The polyps that live inside of this bark are small and gelatinous, have six tentacles (unlike most other corals which have eight). These polyps will sting any small animals that float by. The polyps of cnidarians have an oral disk in their center surrounded by six tentacles. Black corals are carnivorous, with the coral polyps allowing it to feed mostly on meiofauna.
Their skeletons are firmly attached to the seafloor. They will frequently grow where currents flow, which allows them to feed on the plankton that is swept by. The reason that they are fan-shaped is to catch this plankton. Many corals also have an adaptation where they have polyps only on the downstream side of the coral, allowing them to feed on more animals without wasting energy on unnecessary polyps.
Life Cycle & ReproductionEdit
Due to the slow life cycle and deep-water habitats of black coral, little is known about its life cycle and reproduction. 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. It builds a colony by directly creating more 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.
Sexual reproduction happens later in life, after the coral colony is established. A colony will produce both eggs and sperm, which meet in the water to create larvae that use currents to disperse and settle in new areas. 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 that attaches it to the seafloor. The coral will then begin to bud, which will create new polyps, which will eventually form a colony. In some black corals that have been closely examined, colonies will grow roughly 6.4 centimeters (2.5 in.) every year. Sexual reproduction will first occur after some 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 black coral 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 "radial growth rates are as low as 4 to 35 micrometers per year and that individual colony longevities are on the order of thousands of years".
Black corals around the world provide a unique environment for crustaceans, bivalves, and fish. Whip coral (Cirrhipathes species), for example, host as many as six other species. Whip coral gobies and barnacles will permanently inhabit the skeleton. The goby and shrimp can quickly hide on the skeleton's opposite side when a threat approaches. Other fishes, such as gobies and damselfishes, lay their eggs on the skeleton. The damselfish will then bites off the polyps to expose the nesting site.
Human use and HarvestingEdit
Black corals have historically been associated with mystical powers and medicinal properties, though more recent harvesting has been for use as jewellery. Many Indo-Pacific people believe that black coral has curative and anti-evil powers. Black coral, however, is not the best substance for jewelry because it is a soft coral as opposed to a stony coral. This causes jewelry made with it to dry out and break.
The best studied and regulated black coral fisheries are in Hawaii, where harvesting has been conducted since the 1960s. In the Caribbean harvesting is typically conducted to produce jewellery for sale to tourists, and has followed a boom-and-bust cycle, where new black coral populations are discovered and overexploited leading to rapid declines. For example, Cozumel, Mexico, was famed for dense black coral beds that have been harvested since the 1960s leading to widespread black coral population declines. Despite better black coral management in Cozumel, including no harvesting permits issued since the mid-1990s, the black coral population had failed to recover when assessed in 2016. 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), species that are not necessarily threatened with extinction, but may become so unless trade in specimens of such species is subject to strict regulation in order to avoid utilization incompatible with the survival of the species in the wild.
List of families according to the World Register of Marine Species:
- Family Antipathidae Ehrenberg, 1834
- Family Aphanipathidae Opresko, 2004
- sub-family Acanthopathinae Opresko, 2004
- sub-family Aphanipathinae Opresko, 2004
- Family Cladopathidae Kinoshita, 1910
- Family Leiopathidae Haeckel, 1896
- Leiopathes Haime, 1849
- Family Myriopathidae Opresko, 2001
- Family Schizopathidae Brook, 1889
- Abyssopathes Opresko, 2002
- 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
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