Evaluation of the potential interaction between microplastic distribution and biodiversity richness along the coast of the Western Ionian Sea

The presence of microplastic particles (MPs) in the Mediterranean Sea has been widely reported, but their ecological risk in the marine ecosystem have not been completely addressed. With this purpose, the MPs distribution in the coastline waters of the Western Ionian Sea were investigated for the first time. Considered a hot spot of biodiversity and important resting and nesting sites for birds, this area is heavily interested by anthropogenic pressure. Simultaneous visual census of several marine species and manta trawl sampling were performed during a cruise carried out in 2017, to provide an assessment of biodiversity richness and MPs presence. Species richness, Shannon index, and evenness were computed to determine the biodiversity of the studied area. MPs collected were isolated and characterized by shape, size, color, and chemical composition. All data from field surveys were analyzed in Quantum GIS platform. Kernel density estimation was overlapped with marine litter densities to obtain a preliminary risk assessment. In total, 380 sightings were recorded for a total of 17 species: five species of Odontocetes and twelve species belonged to different taxa such as birds and marine turtles. The highest values of biodiversity in terms of species richness and Shannon index were observed in the Gulf of Noto and the Gulf of Augusta, located in the southern part of the studied area. Taking into account the MPs distribution, the highest concentrations of MPs were found in the waters facing Syracuse and the Gulf of Augusta, with an average abundance of 0.10 ± 0.06 items/m2. The overlap between the hotspots of biodiversity and MPs occurrence represents a preliminary contribution to the risk assessment of marine organisms’ exposure to microplastics and may contribute to the identification of sensitive areas where mitigation actions to tackling the plastic pollution are needed.