Marine litter in Sardegna: valutazione dello stato dei rifiuti bentonici come contributo alla Marine Strategy Framework Directory
Anthropogenic debris are known to be present in all marine habitats, from coasts to the most remote points of the planet like deep sea floors and poles. In spite of the growing interest from the political and scientific community regarding this spreading threat, the knowledges on marine litter status still remain fragmentary. Most of studies have been carried out on the sea surface and on coastal habitats, whereas there are few information available about the assessment of anthropogenic debris on the sea bottoms. This PhD thesis aims to evaluate the state of benthic marine litter in terms of composition, density and abundance along the continental shelf and continental slope of FAO Geographical Sub Area 11: Sardinia Island (NW Mediterranean Sea) according to Marine Strategy Framework Directive. Soft bottoms and rocky habitats have been investigated separately by mean of two different sampling methods (trawling and ROV video transect). Trawl surveys are defined as the most appropriate way to collect litter on sandy and muddy seafloors. Within the MEDITS (International Mediterranean Trawls Survey) framework, three years repeated survey permitted the acquisition of a marine debris data in a wide bathymetric range. Uni and multivariate analyses were used to test differences between \inshore and offshore habitats and between geographical zones in terms of litter amount. Results highlighted that, among the 302 investigated stations, plastic resulted by far the main component in terms of occurrence, density and abundance. Concentration of debris derived from land- 2 based activities tends to decrease as we move farther from the coastline. Anthropogenic Marine-based activities are supposed to be the main cause of the sudden increased values of debris observed in the deep habitats, which was investigated through the Deep Sea Cruise PSP15 on a bathymetric range comprise between 800-1600 m. The behaviour of fishermen observed and recorded emphasizes the necessity of a change in the management policy for the conservation of the environment. Investigation on rocky habitats have been carried out through the non-invasive technique of ROV footage. All canyons and pinnacles surveyed, showed the presence of anthropic pressure in terms of marine litter. Discarded fishing gears are the main components of all litter observed. Distance from coastline do not cause significant difference of the variation of debris density. In the rocky bottom investigated 26.5% of marine litter damaged the benthonic coral community, indeed urgently needing special protection measures. Our results constitute an important and needed set of information regarding the treat of marine litter in an high ecological value area such as the Mediterranean basin. As a result these information are useful for future spatio-temporal comparisons, as well for a collaboration to create a unique dataset as required by the MSFD, considered a fundamental tool for the development of proper conservation measures.