Marine litter pollution impacts the sustainability of coastal mangrove ecosystems; an assessment via index-based approach

Globally, the detrimental effects of anthropogenic marine debris on mangrove ecosystems have drawn considerable scientific and public concern. Yet, in Sri Lanka, where mangroves represent a vital component of coastal resilience and blue carbon storage, the in-depth research on litter contamination in mangrove ecosystems and its ecological consequences remains poorly studied. With that motivation, this present study examined the abundance, composition and pollution status of marine macro litter (>2.5 cm) and impacts on mangrove vegetations at four mangrove sites in Sri Lanka (Kallady, Negombo, Kandakuliya, and Balapitiya), located along the coastline of the northern Indian Ocean. Clean Coast Index (CCI), Plastic Abundance Index (PAI), Hazardous Item Index (HII), and Environmental Status Index (ESI) were used to evaluate the mangrove floor pollution levels. A total of 6,527 litter items were collected from four beaches representing 8 typologies. The average density of the litter collected was 0.47 to 0.87 items/m 2 . Plastic items constituted the majority of litter found, accounting for 60%. According to the CCI, four mangrove areas were classified as 'moderate' and 'dirty.' All locations fell under category 'II' on the III, indicating the presence of some hazardous marine debris scattered across sites. The PAI indicated 'low' to 'moderate' plastic contamination, while the ESI classified all sites as having a 'bad' environmental status. Correlation analysis revealed a strong positive relationship between total litter density and physical damage impact categories, including damaged roots, leaves, and branches. To conserve these valuable habitats, the study recommends taking remedial measures to reduce incoming litter loads and to remove existing litter from the mangroves, despite ongoing awareness and cleanup efforts.