Broad-scale distribution of marine benthic litter in shallow waters along the Turkish Aegean coast: a SCUBA-based assessment

Abstract Purpose Marine litter, particularly benthic macro debris, poses persistent ecological and socio-economic threats to Mediterranean seafloor ecosystems. This study addresses critical knowledge gaps in the spatial distribution, composition, and accumulation characteristics of benthic litter along the understudied Turkish Aegean coastline. Methods We conducted the first large-scale, depth-stratified SCUBA-assisted assessment of benthic macro litter across 326 stations along approximately 1600 km of the Turkish Aegean coast. Surveys were performed at six discrete depth levels (5–30 m) following MSFD and UNEP/MAP protocols. Litter items were classified into nine standardized material categories, and both abundance (n km −2 ) and mass (kg km −2 ) metrics were quantified. Multivariate statistical analyses (PCA and PERMANOVA) were applied to examine spatial and depth-related patterns in litter distribution. Results A total of 822 litter items (4147 kg) were recorded, corresponding to mean values of 77.4 n km −2 and 383 kg km −2 . Plastics dominated numerical abundance but contributed relatively little to total mass, whereas metal and concrete debris accounted for a disproportionate share of mass. Shallow stations (5–10 m) were characterized by higher abundances of lightweight litter associated with nearshore activities, while deeper stations more frequently contained heavier debris linked to maritime and aquaculture-related operations. Spatial variability in litter accumulation was primarily associated with material composition and localized human activities rather than broad administrative divisions. Conclusion This study provides the first harmonized and policy-relevant baseline for benthic litter along the Turkish Aegean coast. The findings highlight the importance of integrating mass-based indicators alongside abundance metrics to better assess ecological risk and inform management strategies. SCUBA-assisted surveys are shown to be a robust and complementary approach for monitoring benthic litter in shallow, heterogeneous coastal environments within MSFD/UNEP-aligned frameworks.