Corals

Red Coral (Corallium rubrum) is an octocoral of the Coralliidae family, common in the Mediterranean Sea and the Eastern Atlantic Ocean.

Some claim that the word “coral” comes from the Greek korallion, meaning “hard skeleton”, while others suggest it derives from kura-halos, the Greek for “human form”.

This is the only species of the Corallium genus that lives in the Mediterranean Sea, from Greece and Tunisia to the Strait of Gibraltar, Corsica, Sardinia, Sicily and the Balearic Islands. It is also present in the Eastern Atlantic Ocean, off Portugal, the Canary Islands, Morocco and the Cape Verde Islands.

Its appearance and colour vary depending on its location and the depth of the sea where it lives.

It needs particular conditions for life, such as constant salinity of the sea, only slightly moving waters, and light that is not too intense. Excessive amounts of suspended deposits in the water also affect its survival.

It lives preferably in dark and sheltered places like caverns, crevices or underwater cliffs, at depths between 20–30 and 200 metres.

This coral is usually bright red in colour, but sometimes white, brown or black varieties can be observed. It often forms branched colonies that can grow as high as 20–30 cm. Corals have a skeleton made from calcium carbonate, which is very hard and prized as a material for the production of jewellery, and this skeleton is covered by a layer of soft tissue called the “coenosarc”.

Corals feed on plankton and suspended organic substances captured by the tentacles of the polyps, which in turn are covered by thousands of ectodermic cells called “cnidocytes” that contain a stinging substance to paralyze prey. The polyps are white and transparent, only a few millimetres longs, and with eight tentacles edged with side-branches called “pinnules”, which can be seen when extended to catch prey.

Corals reproduce both asexually and sexually, releasing larvae that - after an embryonic stage of about one month - attach themselves to a hard surface. They then grow about 3-4 cm in height and 0.50-0.80 mm in diameter every year.

Even though coral harvesting has been halved over the last ten years, the situation of the Red Coral in the Mediterranean Sea is still at risk. An appeal for greater attention to this problem was made by a group of United Nations Environment Programme (UNEP) researchers meeting in Tabarka, in Tunisia, to discuss how to best protect this species of marine life, which in Italy can be found in the marine reserves of Cape Caccia in Sardinia, in the Tuscan Archipelago and at Portofino in Liguria.

Every year some 70 tonnes of Red Coral are harvested in the Mediterranean, a quantity that is still too high. This excessive and uncontrolled harvest has been curbed to a certain degree by national and international laws and also by a network of protected marine reserves. Coral populations are still however threatened primarily by illegal harvesting, often carried out with destructive devices like the “St Andrew’s cross”, a cross-like instrument once made in wood, but more recently from steel, which “ploughs” the seabed, or directly by divers. Other threats come from pollution and climate change, which raise seawater temperature.

The best known and most exploited coral populations are those that live near coasts, as experts have explained. “Corals are not on the conservation list,” explains Abdel Rahmen Gannoun, the head of the UNEP/Mediterranean Action Plan biodiversity centre in Tunis. “But their high economic value or the charm they have over collector divers have resulted in over-exploitation of the deepest parts of the ocean floor. In some parts, coral reefs have completely disappeared,” as for example in the area of Tabarka and along the adjacent coasts of Algeria.

Coral colonies grow very slowly: to reach a diameter of one centimetre, a coral branch needs about 40-50 years, and an average of 20 years to grow in height by four centimetres.