Posidonia oceanica is an endemic seagrass of the Mediterranean Sea, forming extensive meadows and providing valuable ecosystem services underwater as well as on the shore. P. oceanica constantly generates new leaves while shedding the older ones. The latter may be deposited on the shoreline, forming “banquettes” that exhibit variable thickness, ranging from a few centimeters to several meters. These deposits act as natural barriers against coastal erosion, preventing sand loss and dissipating wave energy. Moreover, the degradation of the washed-up leaves releases large amounts of nutrients, relevant for the coastal food web. However, the presence of banquettes in touristic areas is often perceived as a nuisance, thus leading to their removal by local administrations. This study proposes a multidisciplinary approach for the assessment of P. oceanica banquettes along the coastline of the Campania region (Southern Italy), estimating their biomass and the associated concentrations of nutrients and other chemical elements, with the final aim to assess the potential loss of natural capital and ecosystem services due to their removal. Regional estimates show that approximately 40 tons of C are stored annually in the beached biomass, representing a potential carbon loss associated with their removal. The results highlight the crucial role that P. oceanica banquettes play in the blue carbon cycle and provide valuable insights to support their sustainable management.