WHAT ARE BLACK CORALS?

They are marine invertebrates creating colonies of hundreds of identical individuals, called polyps, similar to small sea anemones, which are physically connected and function as a single unit. Black corals can grow following different, often tree-like, patterns, where polyps usually measure only a few millimetres in diameter. They are radially symmetrical with six tentacles surrounding a central mouth, the only opening to the stomach, or coelenteron, through which both food is ingested, and waste expelled. Black corals colonies can reach heights up to 3 m, or even more, in some species, whereas other species are no more than 10 cm.

Black corals species are typical of deep waters, although many species can live in a wide range of depths (nearly 75% of them can only survive at depths below 50 m). With similar morphologies to real trees, coral communities may form dense three-dimensional habitats over large areas of the Canary Islands, from 30-40 metres deep, creating real "underwater forests", which modify the landscape and influence the presence of other fauna and flora, thus functioning as true "bioengineers" of marine ecosystems.

Unlike other corals, such as those from the Great Barrier Reef in Australia, whose skeleton are mainly built of calcium carbonate, black corals have a skeleton composed by proteins (around 50%) and chitin, a flexible and resistant compound, which also make up part of the cell walls of fungi or the skeletons of many insects and crustaceans. Despite having different appearances and striking colours due to the polyps, the skeleton of these animals is usually black (hence their name), and may be covered by a series of microscopic skeleton spines which, in addition to reinforcing the skeleton's resistance to torsion, are also used to differentiate species. This is why black corals are also known as "thorn corals".