One-Year Evolution of a Mediterranean Sandy Beach with Posidonia oceanica Banquettes (Arborea, Sardinia, Italy)

Sandy coasts, representing 40% of global shorelines, are essential for coastal defence and ecosystems. Natural solutions are increasingly studied to provide beach protection while enhancing ecosystem services, such as seagrass deposition on the coast. This study investigates the morphological evolution of a beach characterised by a low human impact, where Posidonia oceanica is present and forms banquettes. Fieldwork campaigns, including topographic surveys and drone mapping, were conducted over 1.5 years. A storm during one campaign led to the formation of extensive Posidonia banquettes, particularly in the southern part of the beach, a trend observed in all surveys. This distribution influenced erosion trends, with long medium-term analysis showing overall erosion, especially in northern areas with fewer banquettes and a dune retreat of around 3 meters. These findings highlight the critical role of Posidonia banquettes in protecting against dune erosion, at least locally, although significant erosion over 1.5 years occurred in the whole studied area, suggesting that further investigations are needed.