BLACK CORALS ARE PROBABLY BEST KNOWN AS SHINY, JET BLACK JEWELRY, but in their underwater habitats as living coral they’re more likely to be found in shades of soft reds, greens, yellows and other colors. They’re not stony corals – they grow in complex linear structures resembling trees, bushes or sea fans.
The “black” part is the protein-based chitin that comprises the skeletons on which dense colonies of identical, individual polyps reside. In other words, living black corals show off the hues of their polyp communities and aren’t obviously black.
IN ALL OCEANS, AT ALL DEPTHS
Some 280 species of black corals are found worldwide in waters as varied as arctic seas and tropical reefs, at depths shallow (say, 20 feet/6 meters) and deep. The deepest ever spotted is at some 5 miles/8,600 meters, but the corals are more typically located between 100 feet and 1,000 feet.
Like most variations of corals, they can provide shelter and habitat for other marine denizens, like crabs, shrimps and brittlestars, a particularly significant service in the deeps where suitable substrates may be rarer.
Because of their value as “gems” – and, historically, for purported curative powers – black corals have been harvested from wherever divers could get to them – meaning that today flourishing black coral stands are more likely to be found in deeper waters. And because over-harvesting has placed them at risk, they’re protected by international law.
NOT YOUR AVERAGE CORALS
Black corals are members of Order Antipatharia. As tiny sac-shaped animals that send tentacles out into the current to capture passing plankton, they share six-tentacle architecture with reef-building stony corals (Order Scleractinia) but live their lives on the surfaces of their chitinous stems rather than within the protective calcium corallites Scleractins build.
They somewhat resemble familiar sea fans, rods and plumes, but differ from those members of Order Gorgonia, who live embedded within their chitin-based skeletons and extend eight tentacles into the current through apertures.
And Antipatarian polyps themselves are different in shape from other corals – not cylindrical but sometimes compressed, sometimes star-shaped or sometimes stretched out along the branches the live on.
Unlike most coral polyps they lack the flattened oral discs surrounded by tentacles; non-retractable black coral tentacles extend from differing levels on the polyps’ sides.
SHAPES AND MORE SHAPES
Black coral shapes are frequently compared to trees, with convoluted branching that seems to take sudden sharp turns. Black coral stems, rather than continuously lengthening, may stop growing and start new branches off the side. Some variations may take the shape of bushes, whip or wire “bottle brushes” – central stemmed structures with intricate branches.
The can grow in large clusters or solitary specimens, ranging in size from 10 cm to 3 meters. Taxonomically, they’re currently placed in seven families that tend to specialize in differing depths – two shallow, two intermediate and three in deep waters. According to one source, the best quality for creating jewelry is found at depths of 50 meters or more.
THE WISDOM OF AGES
Black corals are phenomenally slow-growing and also phenomenally long-lived – their skeletons grow with concentric circles that can be counted like a lumber tree’s growth rings. Based on a sample collected near Hawaii, the oldest known black coral is a stand of Leiopathes annosa identified as more than 4,000 years old.
Unlike its stony coral cousins, black corals are not invested with photosynthetic algae that jump-start stony coral growth. This aligns with both the slow rate of Antipatarian growth and its penchant for deep sea living.
THE SILLINESS OF THE AGES
Along with their allure as jewelry, historically some cultures have regarded black corals as possessing medical and magical powers – the term “Antipatarian” comes from the Greek for “against disease. Traditional non-decorative uses ranged from treatments for scorpion stings to charms for fending off evil spells.
Generally, today all black coral is protected under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) adopted by more than 80 nations in the 1970s. Black coral jewelry can still be purchased in locations like Hawaii and the Caribbean but its collection and trade is closely controlled.
PRINCIPAL SOURCES: Reef Coral Identification, Florida, Caribbean, Bahamas, Paul Humann, Ned DeLoach; Marine Biology, Fourth Edition, Peter Castro, Michael Huber; Indo-Pacific Coral Reef Field Guide, Gerald Allen, Roger Steene; Coral Reef Animals of the Indo-Pacific, Terrence Gosliner, David Behrens, Gary Williams; Spotlight on Antipatharians (Black Corals), Dennis Opresko, Smithsonian National Museum of Natural History; Black coral (Leiopathes glaberrima), Wildscreen Arkive; Yellow Cup Black Coral, Oceana; Black Corals of Hawaii, NOAA Ocean Explorer; Newly Identified Black Coral Can Live for Over 4,000 Years, CBS News; Black Coral, Nature.
Black coral (Leiopathes glaberrima)