Citizen science data reliability enhancing scientific research: insights from an 11-year study in the Mediterranean Sea

The present study aimed to investigate the effectiveness of recreational citizen science in biodiversity monitoring. The goal was to evaluate whether a minimal training protocol can maintain data quality while engaging large numbers of volunteers. Data from two projects were used (SPA, 2002-2005 and DUE, 2017-2023), and seven parameters were analyzed: Accuracy, Consistency, Percent Identified, Correct Identification, Correctness of Abundance Ratings, Similarity Index and Reliability. All parameters achieved an average score between 40 and 80%. The lowest-scoring parameters were Similarity Index and Consistency, and those with the highest scores were Percent Identified and Correctness of Abundance Ratings. Results showed that recreational citizen science projects can produce generally reliable data for biodiversity monitoring, with room for improvement in overall data consistency. This supports the notion that the recreational citizen science approach can support scientific research when carefully tailored to the volunteer skills required for the specific project. While more extensive training for volunteers could increase the consistency of the data collected, it may reduce volunteer participation. This could limit project reach. Hence, a balance must be achieved between volunteer engagement and data quality to further improve the effectiveness of recreational citizen science projects.