Distribution and composition patterns of plastic pollution in small islands subjected to different human pressures along the highly connected waters of the NW Mediterranean Sea.

One of the tools to protect Mediterranean biodiversity was the creation of an extensive network of Marine Protected Areas. That those areas are not exempt from plastic pollution has extensively been demonstrated whether they are characterized by a specific plastic composition if compared to not protected areas is currently a topic of discussion. This research aims to evaluate plastic spatial distribution and composition patterns along the surface waters of small islands of the Western Mediterranean Basin subjected to different human pressures and protection status. We studied the spatial distribution of floating plastics by performing 65 surface trawls, carried out using a Hydro-bios manta net coupled with a 335-μm mesh, along the coastal waters of a remote protected archipelago, Columbretes Islands (NW Mediterranean Sea), a protected archipelago located in a high anthropized environment, Cabrera MPA (Balearic Sea), and protected and unprotected areas of two touristic Islands, Mallorca and Menorca in the Balearic Sea. 10637 plastics were identified along the study area and a subset was categorized according to shape, size and polymer. Plastics were found at each sampling site and in all samples. No microscale nor mesoscale variability in plastics abundance was encountered throughout the study area where similar values were found in remote protected areas with no local land-based contamination sources [0.04 (±0.03) items/m2] and in anthropized areas [0.04 (±0.07) items/m2]. Results suggest that floating plastics, in a region such as the NW Mediterranean Sea, strongly exposed to human stressors and highly connected waters, are homogeneously distributed regardless of land uses. Differences were found in plastic size, shape, and polymer composition. Remote islands showed the highest number of fragments reaching percentages higher than 90%, the lowest percentage of film summing up to less than 3%, a lower microscale variability, and the presence of small items with sizes ranging from 2900 μm to 163000 μm not detected in the more anthropized areas. The percentage of film and plastic size increase according to the level of human pressure. Small fragments are the product of fragmentation processes, driven by photooxidation, of larger plastics to smaller ones. Films, due to their volume/surface ratio are suitable for biofouling favoring their faster removal from the sea surface to the seafloor. The lower abundance of film observed in the studied remote protected areas combined with a consistent abundance of small fragments suggest that plastics detected within these waters could be more aged and be arriving from distant sources when compared to plastics detected in more anthropized areas, such as of the Balearic Archipelago, closer to potential marine debris sources and previously described as plastics “retention area”. Remote areas showed a different polymer composition, with a higher percentage of polystyrene, extensively used in the fishing industry that could represent an important contamination source for those areas. Finally, data from this research can contribute to consolidating scientific evidence available for the elaboration and monitoring of future management plans focused on the mitigation and prevention of plastic pollution in marine protected areas