Contrasting macro- and meso-litter accumulation in managed and unmanaged beach sectors of the northwestern Adriatic Sea.

Beach management practices are widely implemented in coastal environments, yet their association with litter size structure remains poorly understood. We evaluated macro- and meso-litter across vegetated (unmanaged) and non-vegetated (managed) beach areas along the northwestern Adriatic coast (Italy) through seasonal stratified surveys comprising 448 plot-level sampling events across 112 plots. Meso-litter accounted for approximately 84% of all recorded items. Negative binomial generalized linear mixed models revealed a significant interaction between litter size class and area type (p < 0.001). Macro-litter abundance was 53% lower in non-vegetated areas (p < 0.001), whereas meso-litter abundance did not differ significantly between area types (p = 0.539). Binomial mixed models further indicated a higher predicted proportion of meso-litter within the combined meso- plus macro-litter total in non-vegetated areas (OR = 2.70, p < 0.001), revealing a compositional shift toward smaller debris fractions in managed beach sectors. These findings suggest that beach management is associated with changes in litter size structure and that monitoring approaches based exclusively on macro-litter may not fully capture variation in coastal litter composition. Incorporating meso-litter into monitoring programs could therefore improve assessments of coastal litter dynamics and support more comprehensive management strategies.