Deep Sea Corals: Black Corals

 
Squat Lobsters on Black Coral. Image credit: NOAA's National Ocean Service

Black corals, contrary to their name, do not appear black but instead come in a range of colors including red, orange, white and green. The name comes from their skeleton, which is indeed black. Black corals belong to the order Antipatharia, a hexacoral, and occur all over the world at a variety of depths. Black corals differ from stony corals, another order of hexacoral, by having a flexible skeletons made of protein and chitin, a fibrous substance that makes up a majority of exoskeletons of arthropods and fungi cell walls. This compound allows them to move in the current, unlike stony skeletons with their rigid frames. The compound of black coral skeleton serves another function, as a record keeper. Their skeletons grow, similar to tree rings, cataloguing changes in their environments and allowing us to see how oceans of the past may have been composed. 
 
Black corals are very long lived. An individual discovered off the coast of Maine is about 4,600 years old, with the oldest Gulf specimen around 2,000 years old.

Some species of black corals face unique threats  compared to other species of deep water coral. Historically, these species have been harvested for making jewelry, as the skeleton can be polished to reveal high luster pieces. Most of this activity has historically taken place in Hawaii, where the species are common in shallower water. 
 
Black whip corals
Black whip corals (left) are, as their name suggests, whip-like. This type of black coral has many other names including black wire coral, and less commonly spiral or coil coral. They have very thin and spiraling central skeleton and do not branch as other black corals do. While they need to attach to a hard substrate, it often looks like they are growing out of sediment as it piles around the base of their thin stalk.

In the Gulf, black whip corals can be found from the shelf edge at 250 feet, down to the deep sea, to at least 3,000 feet.

 

 

Sources: http://oceanexplorer.noaa.gov/explorations/03mountains/background/octoco... http://ocean.si.edu/deep-sea-corals; http://ocean.si.edu/corals-and-coral-reefs; http://oceanexplorer.noaa.gov/explorations/06laserline/background/blackc...http://lophelia.org/case-studies/the-gulf-of-mexico/the-gulf-of-mexico/2...http://www.whatsthatfish.com/fish/giant-black-coral-whip/1296; http://oceanexplorer.noaa.gov/explorations/02hawaii/background/corals/corals.html; http://www.marinespecies.org/aphia.php?p=taxdetails&id=283903

Hannah Leis is GRN's Fisheries Associate.

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