Quels rôles joue la banquette ?

The banquettes that form on the beaches from dead Posidonia leaves deposited by the sea support biodiversity and play a major role in limiting beach erosion.

This protection is done thanks to the way in which Posidonia leaves entangle themselves very tightly,  which reduces the  impact of the waves.  The elasticity of Posidonia banquettes lessens the strength of the waves and protects the sand that remains trapped below.  The same occurs in the water, thanks to Posidonia meadows, which dissipate the wave energy  when they are sufficiently developed (in particular as a reef) and limit the effects of swells and currents.

On the other hand, in sandy areas, dead leaves are dragged towards the dunes, which stabilizes them and provides nutrients to endemic plants that develop nowhere else than there.

Photo : Lucas Stofa – Chercheurs en Herbe

Banquettes must not be displaced and the natural cycles of accumulation and recovery by the sea of these banquettes must be preserved.  The removal of dead Posidonia leaves from beaches has indeed been illegal in France since the introduction of the law of 10 July 1976, relative to the protection of nature, implies the protection of the plant both alive and dead.

However, justified removal is sometimes necessary and must make it possible to reconcile the preservation of fragile environments, erosion limitation and welcome beach users.

Compared to algae, marine flowering plants are not abundant.  Only roughly 60 species exist in the world’s seas and oceans, compared to the more than 10,000 species of algae. Despite this, marine flowering plants are dominant species, constructors of seabeds and landscapes and builders of ecosystems with fundamental roles. Posidonia banquettes represent unique formations of our Mediterranean landscapes and are a complex ecosystem on their own that we are just beginning to unveil. 

29% of Mediterranean beach habitats in Europe have been lost in the last 50 years…