The outer, growing portion is actually brightly colored. The inner skeleton of the black coral gives it its name. Unlike the hard skeletons of shallow-water reef-building coral, the black coral have flexible skeletons made of proteins and chitin, the same material as insect shells.
As they grow they lay down new layers, which helps scientists determine their age.
Over the centuries the growth layers of those skeletons record interactions between the surface and the deep sea. Chemicals trapped in the layers give scientists clues about the conditions in the oceans over the years.
"Despite living at 300 meters and deeper, these animals are sensitive to what is going on in the surface ocean because they are feeding on organic matter that rapidly sinks to the sea floor," Prouty said.
"Deep-sea black corals are a perfect example of ecosystems linked between the surface and the deep ocean. They can potentially record this link in their skeleton for hundreds to thousands of years," Prouty said.
But growing for 2000 years has it's disadvantages.
"Since longevity is a key factor for population maintenance, recovery from a disturbance to these ecosystems, natural or man made, may take decades to centuries," Prouty said.
Coral can be damaged easily by certain oil exploration and fishing practices. It is also a valuable commodity for jewelry makers. It's even Hawaii's state gem.
"The flexibility and shiny luster of black coral have made it a precious commodity in the coral jewelry trade and international trade is regulated by the Convention on International Trade in Endangered Species of Wild Fauna and Flora," said Prouty.
"In fact, black corals have been harvested for centuries to create charms; the scientific name of the order to which black corals belong, ‘Antipatharia,' comes from Greek roots meaning ‘against suffering,'" said Prouty.
IMAGE 1: Cirripathes sp. Spiral wire coral – Black coral (Wikimedia Commons)
IMAGE 2: A black coral colony showing its namesake black skeleton (Wikimedia Commons)
IMAGE 3: Begleri made of Black Coral and red coral with sterling beads. (Wikimedia Commons)