Ecological status of Posidonia oceanica (L.) Delile meadows in relation to light and noise pollution in the northwestern Mediterranean Sea

Terrestrial and marine ecosystems are increasingly threatened by anthropogenic stressors, often interacting and covarying both in space and time. Understanding their combined impacts is crucial, especially in urban and coastal areas where human activities are particularly intense. Artificial Light at Night (ALAN) and Noise Pollution (NP) are sensory pollutants that affect biological processes at various levels, from organisms to ecosystems. Despite the rapid increase of ALAN and NP over recent decades, few studies have investigated their effects on seagrasses and macroalgae and, to date, none have explored their combined effects. In this thesis I investigated the ecological status of shallow Posidonia oceanica meadows and the associated leaf epiphyte communities under different combinations of ALAN and NP, including the characterization of the level of these pollutants. Monitoring activities on P. oceanica meadows were conducted during summer 2024 at five sites, ranging from urbanized coastlines to MPAs in the Ligurian Sea: four sites were located around Capraia Island and one within Secche della Meloria MPA. NP was measured via underwater recordings, while discrete ALAN measurements were captured with a flatLAN. P. oceanica meadows were characterised for their cover and density. Samples of shoots were then collected for evaluating leaf morphology and the composition of the epiphyte community, in the laboratory. The results revealed the presence of NP, occurring for 50 up to 90% of the recording time at all sites, including the sites within the no-take zone of the MPA. However, no clear trends were found when comparing sites. Univariate analyses identified differences at plant and meadow levels, and multivariate analyses revealed significant variations in the composition of primary producers and invertebrate epiphyte assemblages. This preliminary and exploratory study highlights the importance of monitoring activities and the need for further research to fully characterize and understand ALAN and NP combined effects on P. oceanica meadows.