Geospatial distribution and anthropogenic litter impact on coastal mangrove ecosystems from the Saudi Arabia coast of the Gulf

Mangrove ecosystems are significantly impacted by marine litter pollution, an increasingly important environmental problem. These ecosystems, situated at the interface between sea and land, serve as critical habitats and act as traps for plastic pollution. This study investigated the concentration, source, and composition of marine litter on both the mangrove bottom and canopy along the Saudi Arabia coast in the Gulf. The observed concentration of surface litter ranged from 0.98 ± 0.05 to 2.96 ± 0.25 items/m², with a mean concentration of 1.4 ± 0.61 items/m² (SD; N = 9). The mean trapped litter was 0.79 ± 0.45 items/tree, ranging from 0 to 7 items/tree. Plastic litter dominates the mangrove environment, accounting for 80% of debris items on the floor and 43% of those entangled in the canopy. Single-use plastics were the most prevalent type of litter detected across all surveyed locations. The sediments within the mangrove ecosystem serve as long-term repositories for plastic litter, evaluated through various indices, such as General Index, Clean Coast Index, Pollution Load Index, and Hazardous Litter Index, to assess the cleanliness of the mangrove floor. The Pollution Load Index shows a "Hazard level I," indicating that the mangrove floor is less contaminated. A higher concentration of litter was observed in urban areas with greater population density, likely originating from terrestrial activities like urban runoff and marine activities, particularly fishing.