Assessing shoreline dynamics and beach use in a tropical beach: a citizen science-based approach using CoastSnap

Coastal monitoring is a key to understanding the natural and human impacts on the coastal environment. This work investigates the capabilities and limitations of a citizen science-based approach to assess shoreline changes and beach usage on a tropical beach. The CoastSnap platform enables coastline monitoring based on the participation of coastal communities using smartphones. In May 2024, two CoastSnap stations were installed in a small coastal community (Sisal) located on a barrier island in the northern Yucatan Peninsula (Mexico). Image analysis for the 2024-2025 period shows strong participation, with an average of 1.46 snapshots per day. The images acquired by beachgoers allow for the analysis of shoreline changes, public perception, and beach use. Shoreline positions estimated from CoastSnap-derived images were validated with 23 beach surveys conducted fortnightly using a differential global positioning system. The analysis of images collected by beachgoers allowed for the characterization of shoreline changes (subseasonal and Hurricane Milton), with a high spatial and temporal resolution, on beaches located in the vicinity of a pier. Furthermore, image-derived data show that maximum beach occupancy occurs during the weekends of the holiday periods, regardless the season. A sentiment analysis of the user comments suggests an overall positive perception of this coastal site but also reveals concerns about beach litter pollution and increasing coastal development. These results demonstrate the great potential of this citizen science tool for the low-cost high-resolution (local scale) monitoring of coastal environments in tropical regions.