Posidonia, an underwater treasure that forms forests under the sea

Mataró seabed with posidonia meadows

Its name comes from the Greek god of the sea, Poseidon. It is green and forms underwater forests as beneficial to the future of the planet as tropical forests. Its name?: is Posidonia or "Posidonia oceanica" to scientists.

It is an endemic plant of the Mediterranean, composed of a bunch of leaves, roots and rhizomes frequently hidden under the ground. It covers more than one million hectares, from Cyprus to Spain, according to the Mediterranean Network for Posidonia.A minimum figure however, because data from some countries are lacking, especially on the east and south banks of the Mediterranean, according to this network that brings together scientists, authorities and environmental defenders, among others.

Functions

They serve as a shelter, egg-laying area and nursery for fish species.

Although some only see in it an insignificant herb at the bottom of the water, posidonia has crucial benefits for humans, according to these experts."They serve as a shelter, egg-laying area and nursery for the species of fish that frequent our coasts," they add. A large number of animals, including small invertebrates that serve as food for the fish sought by fishermen, live on posidonia.

It is also "a precious ally in the fight against global warming," says Arnaud Gauffier, program director for the World Wide Fund for Nature (WWF) in France. Thanks to rhizomes, posidonia herbariums function as carbon storage wells.

Aj. Killed

They also contribute to breaking the waves by preserving the coastline from erosion. And even on the beaches they improve the protection of the coasts. "Unfortunately it's a very unknown ecosystem and sometimes people think it's dead grasses that cover the beach and prevent bathing," Gauffier says.

In the Mediterranean, they are increasingly threatened. On the French coastline used by large yachts, more than 7,500 hectares were degraded, according to official figures. "The first cause of such damage is caused by vessels "when a ship launches the anchor that will then hit the bottom with devastating effect and also when it is removed," says Thibault Lavernhe, spokesman for the Mediterranean maritime prefecture.

Posidonia only recovers slowly, a few centimeters per year at most. Faced with this problem, France has banned mooring boats larger than 24 meters in some sensitive areas. The Balearic Islands have done so since 2018 and carry out regular checks.

In this sense, the Balearic Islands are "an example" of preservation, with awareness sessions in schools, says WWF, and even a posidonia festival in Formentera.