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Colours under the sea: corals and gorgonians
Did you know that there were reefs in the Mediterranean?
29/10/2021
When we think about corals, probably tropical waters come to our mind and we imagine the Australian reefs, but did you know that a few years ago there were also reefs in the Mediterranean? Yes, it was a more colourful sea than nowadays and you could enjoy many corals and gorgonians.
Many impacts have caused the decline of these species; climate change and overfishing - especially of red coral for its commercial interest - could be among the most important. Since 1999, massive mortality events of corals and gorgonians have been more frecuent, since they are species that suffer a lot of heat stress, that is, they are greatly affected by heat waves, increasingly hot summers and the general water temperature rise due to climate change.
In any case, there are still spaces to enjoy them. In the Columbretes Islands we can see a small coral reef about 15 meters deep. In Mallorca it is also possible to find reefs, although at twice the depth and with a very localized distribution, especially in the north of the island. Without any doubt, this colour gives a tropical touch to the Mediterranean, where we can find more than 150 species; some of them more accessible to see at a depth of 5, 10 or 15 meters, others are already cold-water coralline species at about 800-1000 meters.
Some may wonder what exactly corals and gorgonians are, as well as the difference between them. Both are invertebrate animals. More specifically, they are cnidarians, like jellyfish - yes! Like jellyfish - and they form colonies of various individuals. Corals are rigid and form reefs, whereas gorgonians create underwater forests. They reproduction is one of the most curious things about its biology. They are dioecious species, that is, they form colonies that are male and other colonies that are female, but cannot be distinguished with the naked eye, but using a microscope. When the water heats up - between May and June -, they begin to reproduce releasing eggs and sperm into the sea; although some species, such as red coral or white gorgonian, are internally fertilized within polyps and then expelled to the sea. Its growth also has differences; for example, the white gorgonian grows faster than the red gorgonian.
Colour is another of the characteristic aspects of these species and something very unique. A curious case is that of the red gorgonian. Although its name indicates the colour red, we can find the same species in tones from purple to yellow, a very curious fact that is still unknown.
As we said, mortality has increased a lot in recent years and, therefore, it is very important to monitor living individuals. If you see any, you can notify it in the project “Warning corals!” specifying, if you can, its affectation level (you will find the protocol on how to do it in the project page). Mortality can be identified because the skeleton of the coral is visible and, in some species, the coloration turns white. Sometimes, in addition, it can be covered with filamentous algae.
To finish, we will give a positive data: corals and gorgonians also have their survival skills and, specifically in Cladocora caespitosa, it has been seen that individuals that seemed dead have recovered - a process called rejuvenation - but they need time and improvement of their external conditions. For this reason, and for so many other things, it is extremely important to reverse the rise in temperatures caused by climate change.
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Want to know more? Listen to the PODCAST episode nº09 "Corales y Gorgonias".
This article was originaly posted at the Mallorca Daily Bulletin.
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Photo:Paramuricea clavata (red gorgonian) by Xavier Mas. Source: Observadores del Mar.