Contribution of Marine Citizen Science Initiatives (MCSIs) in Coastal Environmental Monitoring

The coastal oceans, particularly in developing countries, remain largely unexplored, as most global efforts focus on open seas, resulting in significant data gaps in shelf and coastal waters. Citizen Science (CS) approaches, coupled with increasingly affordable technologies, offer a promising way to monitor the coasts by collecting extensive spatial and temporal data over shorter periods. This study reviewed 1127 marine citizen science initiatives (MCSIs) worldwide, emphasising their contributions to environmental monitoring and coastal observing. Results revealed that only 9% of the reviewed initiatives addressed environmental monitoring (physics, biogeochemistry, cross-disciplinary), with a noticeable global decline in newly formed MCSIs since 2020 across all topics. Environmental monitoring MCSIs were predominantly based in the United States and in global-scale initiatives, whereas resource-limited regions had minimal representation. Temperature, Depth, Salinity, and dissolved oxygen were the most monitored oceanographic variables, and showed strong co-occurrences with other variables. The study highlighted key technologies applied in environmental monitoring, with photography, low-cost sensors, and other oceanographic technologies emerging as the primary tools applied in MCS environmental monitoring. Mobile apps and websites were identified as key tools in facilitating stakeholder engagement, enabling data upload and access. However, data quality control methods were often poorly documented by most MCSIs, affecting the trust in CS-generated data. The study recommends supporting under-resourced regions in adopting CS approaches for coastal observing to bridge the data sparse gap, as well as improving data quality documentation and adopting best practices. MCS has demonstrated a significant potential to complement existing coastal observing systems, as evidenced by examples from New Zealand, Tanzania, and the North-east Atlantic.