Marine litter seen through the lens: photo-identification on beaches as a strategy for coastal monitoring and management

The lack of coastal management leads to economic, social, and environmental problems. In this study, beaches in two municipalities, Laguna and Passo de Torres, located in southern Brazil, were monitored for the presence of marine litter through photographic records. Both beaches experience tourism and fishing activities, with their intensity fluctuating seasonally. Data collection was carried out over the four seasons of the year to assess the density, categories, and spatiotemporal distribution of the debris. A total of 3239 photos were taken across all sampling periods, with the number of photographs per transect varying according to the amount of visible litter. In total, 1694 items were recorded in Passo de Torres and 3935 in Laguna, with an average density of 0.051 and 0.078 items/m², respectively. Frequency analysis identified six dominant categories of debris per municipality, with five in common: plastic fragments, packaging, plastic bags, cigarette butts, and fishing waste. The only difference was the presence of plastic bottle caps in Laguna and rigid packaging in Passo de Torres. Plastic fragments were the most abundant category, present in all recorded images, with frequencies of occurrence higher than 50 % for both municipalities. Despite seasonal and spatial variations, both beaches were classified as “very clean” throughout the year, according to the Clean Coast Index. These results highlight the need for specific management strategies for each municipality, aiming to mitigate local pollution sources and promote coastal conservation.