Macrolitter trapping in mangroves: Insights from forest structure and local community knowledge

Mangroves, globally recognized as critical coastal ecosystems, form fringe, basin, and riverine forests in tropical and subtropical coastal zones, where their aerial roots trap macrolitter carried by currents. This study provides the first large-scale integration of field surveys and community knowledge from 671 interviews to assess macrolitter sources, composition, and abundance in 29 mangrove sites in Colombia. We also examined relationships between macrolitter abundance and forest type (fringe, basin, riverine), species composition, tree density, basal area, and proximity to pollution sources. Residents emerged as the main contributors to mangrove macrolitter, largely because of poor waste management practices. Macrolitter abundance was significantly higher in fringe mangroves (2.5 ± 3.6 items m^-2) compared to basin (0.3 ± 0.3 items m^-2) and riverine (0.2 ± 0.1 items m^-2) mangroves. Forest structural variables showed no significant effect on macrolitter abundance, whereas the distance to the nearest population center had a moderately significant effect. Plastics dominated across all mangrove types (89.6 %-93.1 %); floating items prevailed in fringe and riverine mangroves, whereas heavier materials (glass, metals, pottery) were more common in basin mangroves. These findings demonstrate that mangroves act as natural traps for macrolitter, regardless of forest composition or structure, and are heavily impacted by waste from nearby communities. The socio-ecological approach of this study underscores the urgent need to reform packaging for high-consumption products, improve waste management, and deepen community education as public policy priorities. Strengthening these measures would enhance mangrove conservation and support global agendas on coastal management and pollution mitigation.