Posidonia oceanica wrack intercepts plastic debris: First evaluated evidence on Maltese beaches

Plastic debris constitutes a major solid waste pollutant, endangering the marine ecosystem and contributing to sediment accumulation. The presence of plastics in Posidonia oceanica banquettes poses risks for organisms that rely on this habitat type for shelter and food. P. oceanica meadows offer vital ecosystem services, including habitat provision for marine organisms, oxygen production, CO 2 absorption, climate change mitigation, and seawater filtration. At the end of their life cycle, leaves from this seagrass dislodge and accumulate on shorelines as seagrass ‘banquettes’, i.e. wrack. Inasmuch, P. oceanica banquettes on Mediterranean beaches may serve as indicators for plastic debris pollution in the coastal ecosystem. This study for the first time quantified and evaluated the abundance of plastic debris intercepted by the deposits of P. oceanica banquettes on three Maltese beaches at Qalet Marku, Xemxija, and Ramla tal-Qortin. The highest volume of beached P. oceanica wrack was recorded at Qalet Marku (730.71 m 3 ), which included a mean content of plastic items at 24.75 items/m 2 . At Xemxija, the mean content of plastic items was 102.42 items/m 2 , while the mean content at Ramla tal-Qortin was 32.25 items/m 2 . Therefore, the most polluted beach in terms of plastic pollution was Xemxija, where a high level of anthropogenic activities was noted in the vicinity of the beach. The present study provides a baseline for macro (>25 mm)-, meso (5 -25 mm)-, and micro (<5 mm)-plastics trapped within the banquette of P. oceanica on Maltese beaches. • Qalet Marku beach had the highest amount of P. oceanica banquette material (730.71 m 3 ) • A total of 1913 plastic items were recorded from three Maltese beaches • Plastic items were categorised into macroplastics, mesoplastics, and microplastics • Xemxija was the most polluted beach, in terms of plastic pollution, at 102.42 plastic items/m 2 • Mesoplastics were the most abundant plastics across the three beaches