• 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 are useful even dead, washed up on beaches, where they are a bulwark against erosion.
  • But when summer comes, and it is necessary to clear the way for tourists, they are evacuated and sent back to sea, especially in Cannes.
  • Thus, "these flowering plants decompose in their natural environment instead of being exported to a landfill," notes a specialist.

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 enter the algae family) are useful even dead, washed up on beaches. At least in winter. Agglomerated in a vegetal carpet, they then offer a bulwark against erosion that benefits seaside resorts. But when summer comes, and it is necessary to clear the way for tourists, they are evacuated.

In recent years, instead of landfilling, the town hall of Cannes, like other localities on the Côte d'Azur, has been taking them to discharge them offshore. Organized a few days ago near the Croisette, this operation, called "clapage", is part of an approach in favor of the environment but especially legal. Because "even dead, posidonia are protected". 20 Minutes explains.

A "major ecological role" even after his lifetime

In Cannes, it is especially on the beach of Gazanière, at one end of the boulevard de la Croisette, that these small pieces of leaves washed of all their chlorophyll arrive en masse every year. "Especially when there is a wind from the east," explains Thierry Gaudineau, the director of urban cleanliness at the town hall. "A lot of people call us and ask us to take them off, because 'it doesn't look clean'. But it is not a waste, it is even a very good marker of water quality if there is any, "says the manager. Useful to "stabilize the sand band", they are removed only after the Easter holidays. "Before, to get rid of them, we used a provider who valued them. But, regulatory, we were not in the nails, "admits Thierry Gaudineau.


Endemic to the Mediterranean, Posidonia oceanica is indeed protected, even after its lifetime. According to the city of Hyères, in the Var, these "posidonia banks" washed up on the coast are "the basis of food for many animals", "a particular fauna" composed of "amphipod crustaceans, decapods and isopods". So there is no question of doing anything with it. If they are displaced, 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.

The same text stresses that "the discharge at sea of volumes removed or collected [...] must be systematically privileged." He also specifies that this option, chosen for more than three years by the city of Cannes, but also those Beaulieu-sur-Mer and Golfe-Juan to declutter their beaches, must be organized "after recovery of macrowaste and study of the dispersion of leaves according to currentology, 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-clapet", a barge whose whole or part of the hull opens in two to dump its contents, has been carried out in recent days 7 km south of the island Saint-Honorat. A site chosen with the services of the State "because the bottom is located between 500 and 700 m and that avoids seeing them return to the Coast," notes Frédéric Poydenot, the director of the Permanent Center for Environmental Initiatives (CPIE) of the Lérins Islands and Pays d'Azur.

"In this pit, at this depth, the fauna present is not particularly adept at posidonia leaves [which grow up to -40 m], but we reproduce 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, a little more than 200,000 euros, but which is part of a complete program of preservation of this "green lung". Orders in force since 2020 have been signed to prohibit the anchoring of yachts in these fields of underwater plants. At the risk of tearing them off.

  • Planet
  • Nice
  • Alpes-Maritimes
  • Provence-Alpes-Côte d'Azur
  • PACA
  • Cannes
  • Sea
  • Mediterranean