Uncovering the hidden value of citizen beach clean-ups: a social media-based assessment in Spain.

Beach litter remains a persistent threat to coastal ecosystems, with far-reaching ecological, social, and economic consequences. Although official statistics provide essential information, they frequently overlook the numerous voluntary beach clean-up initiatives led by local associations, schools, companies, and informal groups. This study evaluates the potential of social media as a complementary data source for documenting such activities. Spain was selected as a case study due to its extensive coastline and strong reliance on tourism. Through keyword-based searches and geolocation techniques applied to posts on X and Instagram, we identified 487 beach-cleaning events in 2024, of which 458 (94%) were absent from official registries. These data reveal spatial and temporal patterns not captured by traditional monitoring systems, demonstrating the added value of user-generated content for coastal stewardship assessment. We also estimated the economic contribution of these initiatives from €1.13 to €2.86 million, depending on the approach, representing approximately 0.71-1.80% of Spain's annual public expenditure on beach litter removal. Beyond their measurable economic and ecological value, beach clean-ups promote social participation, environmental awareness, and engagement in marine conservation. Overall, our findings show that social media monitoring can effectively complement official statistics by providing a more comprehensive understanding of the scope and contribution of citizen-led efforts in coastal management and marine-litter mitigation.