IMPACT OF ANCHORING ON POSIDONIA
Impact of anchoring on Posidonia
Densities of five boats per hectare can sometimes be observed in crowded Mediterranean bays during the tourist season, a level clearly above the carrying capacity of some areas. While these densities relate to smaller vessels, the impacts of large yachts are even stronger. The most important environmental issue related to the sector is that it drives degradation of Posidonia meadows, with losses reaching an alarming 30% in some areas (French Riviera, etc.).
Depending on their type, size and shape, anchors can damage fragile Posidonia meadows by tearing or crushing the plants when dropped. The anchor bares the rhizomes, abrades the matte, generates large dead matte areas and facilitates the colonization of alien species. Localized regressions of Posidonia oceanica meadows will progressively increase erosion and chemical change, leading to more important impacts. In addition, if ships are not positioned well against the wave and wind conditions, anchors and chains may drag on the bottom, causing much greater damage.
A 50 m yacht can destroy up to 1500 m2 of Posidonia habitat (a quarter of a football field).
In some areas, the impact of anchoring has become one of the main threats to Posidonia oceanica