Mangrove forests as traps for marine litter.

To verify weather mangroves act as sinks for marine litter, we surveyed through visual census 20 forests along the Red Sea and the Arabian Gulf, both in inhabited and remote locations. Anthropogenic debris items were counted and classified along transects, and the influence of main drivers of distribution were considered (i.e. land-based and ocean-based sources, density of the forest and properties of the object). We confirmed that distance to major maritime traffic routes significantly affects the density of anthropogenic debris in Red Sea mangrove forests, while this was independent of land-based activities. This suggests ocean-based activities combined with surface currents as major drivers of litter in this basin. Additionally, litter was more abundant where the mangrove density was higher, and object distribution through the mangrove stand often depended on their shape and dimension. We particularly show that pneumatophores act as a sieve retaining large plastic objects, leading to higher plastic mass estimates in mangroves compared to those of beaches previously surveyed in the Red Sea.