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Citizen science initiatives and outcomes in plastic pollution monitoring and control in the southern Bay of Biscay.
Summary
Researchers compiled seven years of citizen science marine litter data from the southern Bay of Biscay across beaches, floating zones, and seafloor surveys, finding plastics comprised 77–98% of recorded items and that small plastic pieces (0–2.5 cm) were the single most abundant object type across all three environments.
Marine litter constitutes a significant global environmental challenge that needs to be addressed through international regulatory frameworks and conventions such as the International Convention for the Prevention of Pollution from Ships (MARPOL), the EU Marine Strategy Framework Directive (MSFD) and the Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR) among others; all of which depend on reliable data to assess progress and guide mitigation efforts. Without the involvement of citizen science monitoring, the acquisition of such comprehensive datasets would be practically unfeasible. The South of the Bay of Biscay, where multiple monitoring efforts -both scientific and citizen science- have been conducted, is characterized by distinctive oceanographic conditions and intense anthropogenic activity. This study aims to contribute to addressing plastic pollution by compiling information on marine litter monitored by citizen science programmes across the South of the Bay of Biscay and identifying the main policy instruments, initiatives, and their key outcomes across three domains: beaches, floating marine litter, and seafloor. Beaches were the most frequently surveyed environment, with 1697 monitoring events reported between 2018 and 2024 in the study area. These surveys collected 441,682 litter items, which plastic pieces (0-2.5 cm), being the most abundant object (79,480 items) and plastics accounted for 77.50% of all recorded items. Additionally, the area has been identified as a potential accumulation zone for floating marine litter, with long residence times in its eastern sector; an observation supported by citizen science records which reported 180,474 items across 212 surveys, 97.98% of which were plastics. Plastic pieces (0-2.5 cm) totalling 151,531 items and emerging again as the most abundant objects. Regarding seafloor litter, citizen science monitoring relies on two monitoring approaches: scuba diving and trawling. However, in the study area, trawling is carried out only in Galicia and Asturias, and scuba diving surveys are limited. A total of 31scuba diving surveys collected 65,119 items, with plastics representing a more modest share (36.77%) and glass bottles and jars (19,249 items) surpassing plastic pieces.