Assessing the Limits: Citizen Science Data Accuracy in Underwater Monitoring

Citizen science has become a powerful tool for generating extensive ecological data and fostering public engagement in environmental monitoring and conservation initiatives. In marine environments, where monitoring is challenging due to logistical demands and financial constraints, engagement of recreational divers to citizen science projects offers a promising avenue for expanding data collection efforts over large spatial and time scales. Here, we evaluate the accuracy of ecological data collected by volunteer divers in the Mediterranean region by comparing their observations with those of expert scientists. Using standardized monitoring protocols across multiple sites, we assessed volunteers’ abilities to identify marine species, threats and impacts, estimate abundances, and correctly report species’ absence. Our results reveal considerable variability in the performance of volunteer divers, who frequently misidentified sessile taxa and fish species and failed to detect critical environmental stressors, such as tissue necrosis associated with mass mortality events. Diving experience and site familiarity were found to significantly influence the quality of information reported by non-experts, with experienced and site-acquainted divers demonstrating higher data accuracy. While citizen science has the potential to enrich ecological research and inform management and conservation initiatives, our results demonstrate that, without a prior training and proper data validation procedures, generated records often fail to reliably capture the complexity of variables required.