Vegetated habitats as natural macrolitter traps in an Apulian site along the Southeastern Adriatic Coast: Insights from the Ericaria crinita macroalgal canopy

Marine algal forests are highly productive and biodiverse ecosystems yet increasingly threatened by habitat loss and fragmentation. To mitigate these pressures, identifying the drivers of macroalgal canopy decline is essential. This study examines seasonal variations in abundance and size structure of Ericaria crinita (Phaeophyta) and assesses its role in retaining marine litter. Along the Apulian coastline (Italy, Adriatic Sea), litter abundance and composition were analyzed across four habitats: vegetated low-shore rocky habitats with and without macroalgal canopies, and vegetated and unvegetated emerged beaches. E. crinita abundance remained stable across seasons, while size structure showed significant seasonal variation, with spring as the main growth period and summer as a dormancy phase. The vegetated beach exhibited the highest litter abundance (9.54 ± 0.59 items m−2), mainly originating from land-based sources, whereas the rocky shore without canopy was the least affected habitat. Sea-based litter was significantly more abundant in the rocky shore with canopy and the vegetated beach (2.62 ± 0.32 and 2.50 ± 0.37 items m−2, respectively), compared with the unvegetated beach (0.46 ± 0.14 items m−2) and the rocky shore without canopy (0.17 ± 0.08 items m−2). Recreational land-based activities are the primary source of litter on the beach, while fishing activities mainly impact macroalgal canopies. Dense canopies enhance the retention of larger litter items, as indicated by the positive correlation between large-size litter items and thallus length. The findings highlight the pervasive presence of marine litter and the need for targeted management strategies to mitigate its impacts on macroalgal forests.