Named for the black or dark brown color of its skeleton, rather than for the often bright colors of its living tissue, black coral is a type of deep water organism closely related to sea anemones. New research has revealed that some of the black corals living in the Caribbean Sea are approximately 2,000 years old. White, red, yellow, green, and brown when encountered while alive, these corals are an important part of the ocean’s ecosystem.
Black Coral Basics
Also known as Atipatharians, Black Corals are a group which comprises about 230 known species. Most live in deep, warm water, although some black coral colonies have been found in shallow water areas where there is enough darkness for the corals to thrive. One such place is New Zealand’s Milford Sound, where divers and visitors to the sound’s underwater observatory can get a look at a rare species which normally occurs at depths of 500 meters and beyond, at a depth of just 10 meters.
Among corals, Antipaharians are unique. They are covered in tiny spines that have earned them the nickname of “Little Thorn Coral”, and they prefer to live in dark spaces, one reason they can often be found clinging to the insides of caves and in other areas which are fairly devoid of light, such as around shipwrecks. The black corals you may encounter while diving are a rarity, as the largest black coral forests are found at depths as great as two miles beneath the surface. It is some of these deep water corals which the US Geological Survey Pacific Coastal and Marine Science Center have analyzed to determine its age. When you stop to consider that corals are marine animals and not a form of plant life, the fact that some individuals have managed to survive for thousands of years might amaze you.
Much of the research which has been conducted to date was done using a manned submersible equipped with manipulator arms that collected the samples used for testing. While some of the species found in shallower water can be a few meters tall, most black coral species, including the oldest discovered to date, are only a little over a meter tall, with younger trees being much smaller.
Researchers have determined that these ancient corals grow only 8 to 22 micrometers per year, which translates to between .0003 and .0008 inches annually. Most reef building coral species grow at a still slow average rate of about 10 millimeters each year, but that is lightning fast compared with black corals, which take about 600 times as long as other species to grow. As a comparison, our hair grows about 15 centimeters each year, about 6,000 to 10,000 times as quickly as the slowest growing black coral does. While the fastest growing black coral species discovered grow at an average rate of about two inches per year, that slow growth rate means it can take centuries to reach a significant size.
Scientists have been able to determine the corals’ age by using its skeleton, which is composed of proteins and chitin, and which is flexible, unlike the hard skeletons of reef building corals. As the corals grow, they lay down new layers in a way which has been compared to the manner in which trees age, leaving telltale rings behind them as they become larger. Like trees, the corals’ bodies contain chemicals trapped inside the layers, which provide important clues about the health of the oceans they are found in.
Any type of disturbance, such as deep sea dredging and oil exploration, bottom trawling, and intentional harvest can cause damage which can take decades or centuries to recover from. Many of these practices have caused serious damage to black corals, particularly in areas where it is harvested to be made into jewelry. In Hawaii, black coral is the state “gem” and have been fished heavily since the 1950’s. A dominant feature of the state’s deep coral reef environment, black corals are common to the Au’au channel, which is situated between Maui and Lanai. Surveys conducted after 1998 show that Hawaii’s black coral population is declining due to both fishing pressure and the invasion of snowflake coral, which is taking over in areas where the largest colonies have been impacted by human destruction.
Where to Observe Black Coral
There are many wonderful dive sites throughout the world where you can view healthy black coral. One such site is the Black Coral Wall in Belize, which is also known as the Terrace. Located on northwest Turneffe, this stepped wall begins at a depth of 35 feet, falling to a ledge at 124 feet and then dropping away to third and fourth terraces located at 160 and 190 feet, respectively. The black coral here is lush and can be seen even along the first section of the wall, where a massive indentation forms a large grotto which is dark enough for the coral to thrive.
There are several sites in the Galapagos where black coral thrives; one of the best is Cousin’s Rock, which features a wall covered in black coral at depths no greater than 90 feet. In Hawaii, a cave near the LST wreck on the east side of Oahu holds a rare shallow water black coral forest at a depth of about 70 feet, and Malaysia’s Black Coral Garden, which is just off Mantabuan Island, is located at depths between 65 and 100 feet. The Virgin Islands, Bali, Grenada, the Bahamas, and Grand Cayman are a few of the other places where you can find black coral living on walls and wrecks, and inside caves and grottoes.
If you ever have the opportunity to view a black coral forest while diving, be sure to take it. The corals have an iridescent appearance which makes them appear almost luminescent, and they are nearly always found in environments where gorgonians and other less often encountered species thrive. Remember never to touch it, and if your buoyancy control leaves something to be desired, keep your distance from it and all corals. With careful conservation on the part of divers and others, these amazing creatures can continue to thrive, outlasting us for perhaps thousands of years more.