Dive 02: The Mighty Black Coral

by Tina N. Molodtsova, Shirshov Institute of Oceanology

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Black corals seen during Dive 02 of the expedition. Video courtesy of the NOAA Office of Ocean Exploration and Research, Windows to the Deep 2019.

When we hear the word “coral,” generally we have in mind the stony corals, white coral sand, or the Great Barrier Reef with its colorful fishes. But these are not the only corals in the world. In the deep sea, we encounter many other corals: lace corals, soft corals, gold corals, and black corals. All of them play important roles in deep-sea ecosystems by serving as shelters, breeding grounds, and food for many other animals, fish, or invertebrates. The black corals, or antipatharians, that we saw during the second dive of the Windows to the Deep 2019 expedition are fascinating. They belong to the genus Leiopathes, and the species of this genus have proved to be extremely long living.

When scientists aged a colony of Leiopathes annosa from Hawaii, they discovered that it was more than 4,000 years old, and the samples they aged were not even the biggest nor oldest coral in the area. You have to admit that 4,000 years is a tremendous age. It’s very hard to imagine that this number is real – that 2,000 years ago, at the very beginning of our era, this coral already existed, was perhaps flourishing, and was already very, very old.

When the tissue of the coral in this video was damaged – either by fishing gear or suspended sand – the dark inner bark of the colony was exposed. Other animals began to settle on the surface and grow, and little by little, they took up more and more space. You can see there is not much healthy tissue left on this particular colony, and that the bark is overgrown by sea anemones, barnacles, hydroids, and feather stars.

All species of Leiopathes are extremely vulnerable deep-sea corals which break easily and are almost impossible to restore. Perhaps this fragility is easier to understand when you keep in mind just how many years it took these corals to grow into their current form. But even in death, the coral structures can persist, for a time, as a home and shelter for other animals.

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