Canarias: Black Coral

The prolonged volcanic eruptions occurring through eras gave birth to the Canary Islands. The most eastward islands, Lanzarote and Fuerteventura, are the oldest among them. They emerged between 16 and 22 million years ago in the epoch of Miocene, followed by Gran Canaria, Tenerife and La Gomera that elevated above the sea surface about 14,5 to 8,5 million years ago. The remaining two surfaced in the Pleistocene epoch; La Palma came to the surface around 2 million years ago and El Hierro, being the youngest, appeared 1,1 Mya. Located in the Central Eastern Atlantic, these islands belong within the subtropical fascia.

Tenerife in particular, is surrounded by coral formations, which differ compared to the coral reefs found on the Australian coasts, in the Indian Ocean and the Carribean, because they are formed by the black coral (Antipathella wollastoni). It belongs to the class of Anthozoa and is characterised by a black and flexible skeleton. Unlike the corals of the Great Barrier Reef, the black coral does not live in symbiosis with zooxanthellae that are microalgae which support the corals’ metabolism thanks to photosynthesis. In fact, you cannot find black coral formations in the most enlightened waters as they live between 20 and 1000 m depths. Although it is quite difficult to see them around 20 m depth, they are very common from around 40 m depth on and they have been observed up to 1400 m depth!

The black coral grows irregularly and branches out in all directions, appearing like a real underwater forest. When one thinks of corals, the question whether they are plants or animals pops into the mind. Indeed these forests are constructed by numerous polyps (kingdom Animalia, phylum Cnidaria) of up to 1,5 mm and their colony reaches as high as 1,5 m. The blackish colour is given by the protein-based chitin that constructs the skeleton, encircled by polyps. The different hues of what is considered black are actually shades of red, green, yellow and brown. Additionally, the forest represents an oasis for aquatic life; it is possible to observe diverse schools of fish, rays, angel sharks, turtles and many others.

Credit: Franco Banfi

These colonies are attached to the rocky grounds and feed on plankton that is brought to them by the surrounding currents. As the sea water temperature rises during the summer months, these polyps undertake reproduction called spawning. The entire colony starts to release sperm and eggs at the same time, which rise towards the surface. As the sperm and egg cells join together, they form the embryo that develops into a coral larva known by the name planula. The planula floats in the water column for several days before dropping down to the seafloor. If the substrate for the planula is decent, it attaches to the bottom and grows into a new colony, reaching only a few inches per year.

Although the following video does not show the spawning of this specific species and neither the Canary region, it can help you understand how does it occur.

Antipathella wollastoni is not only found in the Canary waters, but it grows also on the Cape Verde, Ascension, Madeira, the Azores and, finally, in the Mediterranean Sea. In the latter case, it is possible to encounter its colonies in the Ceuta littoral on the southwest of the Mediterranean in the proximity of the strait of Gibraltar.

In the past, black coral was exploited for jewelry purposes. Luckily, it is now under strict government protection. Below you can find a short video on how it was exploited in the past:

Another endangering factor for this particular marine community is certainly the diving activity. There are many scuba diving spots where you can encounter the black coral and divers should be more prudent, as the corals’ growth is slow. Excitement before diving often leads people with little experience to simply go down. However, it is necessary to pay attention, keep the buoyancy and watch the pending gear.

In conclusion, the black coral is certainly a formation worth seeing once in our lives. Its spawning might be one of the most spectacular events occurring below the surface and it is on us to take good care of it.

Hasta luego!

Rakka, M., Orejas, C., Sampaio, I., Monteiro, J., Parra, H. and Carreiro-Silva, M., 2017. Reproductive biology of the black coral Antipathella wollastoni (Cnidaria: Antipatharia) in the Azores (NE Atlantic). Deep Sea Research Part II: Topical Studies in Oceanography, 145, pp.131-141.

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