“The first alerts were reported between August 18 and 19, following violent stormy episodes that crossed the South-East of France”, details the natural park.
“Since then, observations made in different marine protected areas on the Mediterranean coast (Calanques National Park, Port-Cros National Park, Côte Bleu Marine Park, etc.) have converged to highlight a massive episode of gorgonian mortality” , continues the press release.
This “worrying” mortality marked “divers by its magnitude and intensity”, underlines the Calanques National Park, according to which “all the clues point to global warming, with the prolonged increase in water temperature, beyond the tolerance threshold of the species, which causes the necrosis of their tissues”.
Admittedly, the observation of this phenomenon just after the episodes of violent storms which occurred during the week of August 15 “questions”, according to Patrick Bonhomme, project manager within the Park: but “the geographical extent of the phenomenon does not invite to attribute the origin of the mortalities to isolated pollution” of terrestrial origin.
“We know that episodes of sea heat waves affect gorgonians. And we know that it has been very hot in the Mediterranean this summer, with temperatures around 26-28°C over long periods of up to 20 meters, even 30 meters deep,” added Mr. Bonhomme.
“The gorgonians grow very slowly and their vulnerability to climate change is very high,” said Pauline Vouriot, marine biodiversity project manager at the Park.
“In the Mediterranean, following the episodes of ocean heat waves in 1999, 2003 and 2006, many cases of massive mortality of species were observed”, in particular gorgonians or posidonia, indicated a CNRS report from October 2020.
Mediterranean gorgonians, most often purple, “form large colonies that settle on the rocky substrates of the seabed located between 7 and 110 meters deep”, explains the Calanques National Park, noting that they constitute “real animal forests which are home to 15 to 20% of known species in the Mediterranean”.
If the latter covers less than 1% of the ocean surface of the planet, it is home to “18% of all known marine species”, according to a report by the network of Mediterranean experts on climate change (Medecc), and already presents ” the highest proportion of threatened marine habitats in Europe”.