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Anchoring damage on Posidonia oceanica meadow cover: A case study in Prelo cove (Ligurian Sea, NW Mediterranean)

Among the various types of human activities, the mechanical damages resulting from uncontrolled pleasure boats anchoring in shallow coastal waters would appear to be responsible for localized regressions of Posidonia oceanica meadows. This paper aims to describe and quantify the impacts of a large anchoring chains system on the structure of the P. oceanica meadow of Prelo cove (Ligurian Sea, NW Mediterranean). In this study, we provide evidence that this chains system had a negative effect on the meadow cover, generating dead ‘matte’ areas within the meadow. Meadow structure mapping, combined with the use of an environmental index (Conservation Index), which is linked to the proportional abundance of dead matte relative to living P. oceanica, underpins significant differences in the cover and in the conservation status of the meadow between areas characterized by the presence of the chains and areas without the chains. We also show that the chains affected the meadow in different ways according to P. oceanica cover. The approach proposed here, based on thematic mapping and a simple environmental index, provides relevant information for management actions on the conservation of Posidonia oceanica meadows.