Plastic accumulation on a marine protected area: the case study of the Giannutri Island in Tuscan Archipelago.

Following the report of an accumulation of waste on the seabed of the island of Giannutri by divers working in Tuscan Archipelago zone, a multidisciplinary project to study this peculiar accumulation was born, involving institutes of the CNR, ENEA, INGV, University of Pisa and Toulon. The accumulation, noted for several years, is in a circumscribed area at a depth of 15 meters, in front of the island of Giannutri, Tuscan Archipelago. In August 2022, the conspicuous presence of anthropogenic material, mostly of polymeric type (bottles, vials, etc.), was verified. In November 2022, in collaboration with the CNeS (Nautical and Diving Center of the State Police of La Spezia), an underwater photographic mapping and geophysical characterization were performed, video/photographic footage taken and samples retained for subsequent laboratory analysis. In July 2023, the intervention of CASTALIA fleet allow the removal and disposal of all the material, except for a number of retained samples. On all the November and July samples we identified different species of bryozoans and benthic foraminifera, and we analyzed the degradation and aging of the polymeric matrix, in collaboration with Pisa PolyGreenLab group of CNR-IPFC, involved since years in these kind of studies (De Monte et al., 2022). The first results did not reveal the presence of NIS species among those found in the bottles, and instead confirm that all detected species belong to the ones living in Posidonia prairies, suggesting the local origin of these concretions. This would lead to the assumption of an arrival of the material by sea from other areas, their subsequent sinking there (probably due to fouling resulting in a change in the density of the object) and then colonization by local species (Zettler et al., 2013). Interestingly, there was a low taxonomic homogeneity and the presence of a dominating species shown by each of the analyzed bottles; this introduces potential danger, as if bottles leave the Gulf of Spalmatoio of Giannutri and join a larger current to be transported far from the accumulation area, this could lead to some species being carried into uncolonized areas, inducing competition with other species and leading to what is known as a bio-invasion phenomenon (Kiessling et al., 2015). To test this hypothesis, in parallel with the chemical/physical state of the recovered objects, a study of the dynamics of the currents in the area is being conducted through Lagrangian models to understand what forcing factors led to the presence of such an accumulation. In the next few days (April 6 - 10) a campaign will be conducted to check, about 10 months after removal, whether any finds are present in the area again, and quantify them, and at the same time dispersal experiments will be carried out using specially made drifters that have already been tested for the study of surface movements of marine litter in coastal areas (Merlino et al., 2023).