The black or thorny corals (Antipatharia) make up an order of about 230 recognized species, many found in deep water. The colonies often grow in whiplike or branching tree-like formations up to 6 meters tall, supported by a skeletons are made of a hard protein called antipatharin. The skeletons of many species contain dark pigments, and most produce spine-like structures on the surface of the skeleton. Usually the polyps have six nonretractable tentacles, but they can have multiples of six up to 24, arranged in an irregular branching pattern; this is key to distinguishing these corals from the gorgonian corals (octocorals, having eight tentacles), which they otherwise resemble (Kozloff 1990).
Conservation and Management
These corals are heavily impacted by overharvesting for the jewelry trade, and are threatened by activities associated with commercial fishing, such as bottom trawling which damages coral beds. Like other corals they are also susceptible to death and disease due to increased water temperatures and ocean acidification resulting from increased atmospheric carbon dioxide levels. All Antipatharian black corals are listed under Appendix II of the CITES list of endangered species (http://www.cites.org/eng/app/index.shtml). Antipatharian corals support complex fish and invertebrate communities and there is a call for further research on their importance in marine ecosystems (Ospresko and Sanches 2005).
Unlike most corals, it is thought that Antipatharia polyps do not have zooxanthellae (symbiotic algae) dependent on photosynthesis, and thus often live in deep and dark waters (Ospresko and Sanchez 2005)
Most Antipatharian corals inhabit tropical and subtropical regions, although they have been found world-wide, including species in Antarctica.
One genus in the Antipatharia shows extreme longevity. Researchers have recently carbon-14 dated tissue from Hawaiian specimens of the species Leiopathes glaberrima, finding it to be one of the oldest known marine organisms, at more than 4200 years old. In addition, Leiopathes shows very slow growth; radiocarbon testing estimates radial growth rates at about 15 microns per year (Roark et al. 2009)
The name Antipatharia “against disease” derives from an old belief that their skeletons were thought to repel sickness, and were commonly made into healing amulets. Many species of Antipatharia are prized for their beautiful look especially when polished and are commercially valuable. The structure of the skeleton is such that if it is heated, it can be bent (for example, into the shape of bracelets).
(Ospresko and Sanches 2005)