It is not for nothing that Posidonia are so pampered. Considered during their lifetime as the “green lung of the Mediterranean”, where they bring oxygen and serve as a “nursery” for many species, these flowering plants (and yes, they do not belong to the algae family) are useful even dead, washed up on the beaches. Anyway, winter. Agglomerated in a vegetable carpet, they then offer a rampart against the erosion which benefits the seaside resorts. But when summer comes, and it is necessary to clear the way for tourists, they are evacuated.
For a few years now, instead of putting them in landfills, the town hall of Cannes, like other localities on the Côte d’Azur, has been collecting them to reject them offshore. Organized a few days ago near the Croisette, this operation, known as “clapping”, is part of an approach in favor of the environment but above all legal. Because “even dead, Posidonia are protected”. 20 minutes explains to you.
A “major ecological role” even after his lifetime
In Cannes, it is especially on the Gazanière beach, at one end of the Boulevard de la Croisette, that these little bits of leaves washed with all their chlorophyll arrive en masse each year. “Especially when there is an easterly wind”, explains Thierry Gaudineau, the director of urban cleanliness at the town hall. “A lot of people call us to ask us to take them off, because ‘it doesn’t look clean’. But it is not waste, it is even a very good marker of the quality of the water if there is any, ”recalls the manager. Useful for “stabilizing the strip of sand”, they are only removed after the Easter holidays. “Before, to get rid of them, we used a service provider who valued them. But, by regulation, we weren’t in the nails, ”admits Thierry Gaudineau.
Mediterranean endemic species, Posidonia oceanica is indeed protected, even after his lifetime. According to the city of Hyères, in the Var, these “posidonia benches” stranded on the coast are “the basis of food for many animals”, “a particular fauna” composed of “amphipod, decapod and isopod crustaceans”. . So no question of making anything out of it. If they are moved, it must not be for nothing. Since 2021, a joint decree of the ministers of ecological transition, the sea and agriculture, which underlines their “major ecological role”, sets “the conditions and limits under which derogations from the prohibitions of destruction can be granted by the prefects” when they accumulate in particular in shipping lanes.
This same text emphasizes that “the discharge into the sea of the volumes removed or collected […] should always be preferred. It also specifies that this option, chosen for more than three years by the city of Cannes, but also those of Beaulieu-sur-Mer and Golfe-Juan to declutter their beaches, must be organized “after recovery of macro-waste and study of the dispersion of sheets according to the current, for the choice of the site of the new immersion. »
“We reproduce a natural phenomenon”
Off the city of festivals, the “clapage”, whose name comes from the “boat-valve”, a barge in which all or part of the hull opens in two to dump its contents, has taken place in recent days. 7 km south of Saint-Honorat Island. A site chosen with the State services “because the bottom is located between 500 and 700 m and that makes it possible to avoid seeing them return to the Coast”, notes Frédéric Poydenot, the director of the Permanent Center for Initiatives for the environment (CPIE) of the Iles de Lérins and Pays d’Azur.
“In this pit, at this depth, the fauna present is not particularly adept at Posidonia leaves. [qui poussent jusqu’à -40 m], but we are reproducing a natural phenomenon”, notes the specialist. These flowering plants decompose in their environment instead of being exported to a landfill.
In total, as every year now, nearly 3,000 m3 of these seagrass “have been returned to the sea” in recent weeks, welcomes the city of Cannes. An operation that has a blow, just over 200,000 euros, but which is part of a complete program to preserve this “green lung”. Orders in force since 2020 have been signed in particular to prohibit the anchoring of yachts in these fields of underwater plants. At the risk of tearing them off.