A multi-compartment monitoring approach to assess the impact of marine litter in a Mediterranean coastal area.

Marine litter, particularly microplastics, is a growing threat to the Mediterranean Sea, impacting biodiversity and ecosystem health. However, most studies conducted in the Mediterranean Sea have focused on monitoring of only specific environmental compartments, and rarely have highlighted the overall impacts affecting an area. Therefore, using a new multi-compartment monitoring approach and a standardized methodology, this study investigates the abundance, distribution, composition and impact of marine litter on beaches, surface waters, fish and mussels in a coastal area of Tuscany (Italy). Concerning beach macro litter values, significant differences were found among the three beaches analysed, with the highest amount in the Feniglia beach (mean value = 1245 items/100 m). The top items found are cotton bud sticks (32.3 %), which in the winter survey at Feniglia beach, reached a remarkable density of 1983 items/100 m. Microlitter (1-5 mm), was detected in the beach sediments with a mean abundance of 130 items/m. Regarding floating macrolitter, the transect with the highest values was the Feniglia site at 3 nautical miles in autumn (1083 items/km) while for floating microlitter the highest concentration (832,683 MPs/km) was found in front of Scarlino. Of the 234 fish analysed from 5 different species, 67 contained microplastics in the gastrointestinal tract (28 %) with a mean value of 0.4 items per individual. The species with the highest occurrence was the European anchovy (Engraulis encrasicolus) (53 %) followed by the bogue (Boops boops) (40 %). Through the application of the Marine Litter Impact Index (MLII), considering all the compartments analysed, the Feniglia area emerges as the ecosystem most impacted by marine litter (mean MLII = 3.5, high). This study highlights how a multi-compartment monitoring approach is crucial for understanding the complex interactions between land, sea, and biota.