Seasonality influences microplastic occurrence in cultured European flat oyster

Oyster farming is one of the most sustainable aquaculture products in terms of ecological footprint and carbon sequestration, returning high-value seafood largely appreciated by consumers worldwide. As oysters feed phytoplankton and other organic matter filtered from large volumes of water, they are highly exposed to microplastics (MPs). Consequently, they may be considered good bioindicators of water-column contamination and, contemporaneously, a potential risk for human consumption. In this scenario, this study aimed to analyze MP concentration and their characteristics in the European flat oyster (Ostrea edulis) during the different seasons of the year. Two different-sized classes (subadults and adults) of European flat oysters (n=240) reared in a productive plant located in the western Mediterranean Sea, were sampled during four seasons. Changes were monitored in terms of MP quantity (n. of items/individual), concentration (n. of items/gr dry weight), size, and shape (fragments, spheres, and fibers). Results show no significant differences between oyster sizes in the same season, but significant differences emerged when comparing oysters among different seasons. In fact, oysters sampled in summer showed significantly higher MP concentrations compared to the winter one's. Furthermore, the distribution of the MP shapes evidenced significant changes between seasons with spheres decreasing in summer, when fragments increased, while fibers were stable over time. These preliminary results are discussed considering the seasonal variation in local marine hydrodynamism and the flat oyster trophic ecology. Also see: https://micro2024.sciencesconf.org/559699/document