Can citizen science contribute to the evidence-base that underpins marine policy?

Marine legislation is becoming ever more complex, so new cost-effective ways of obtaining and processing increasingly large data sets are required to support evidence-based policy making. Citizen science is one solution, but the uptake of the evidence generated by citizens among policy makers is often limited. Here, the importance of citizen science in delivery of the evidence-base that underpins marine policy was assessed using a series of case-studies. There was no consistent rationale for developing policy-relevant citizen science, but drivers included: lack of existing data, difficulty in collecting data by other means, the use of citizen science data by other organisations, and the capabilities of volunteers. Challenges to the uptake of marine citizen science were identified from policy-maker, scientist and citizen perspectives, and these related to data quality, data access, motivation of volunteers, and physical location. Citizen science has good potential to contribute to the evidence-base alongside traditional monitoring, remote sensing, and modelling, but only if outputs from citizen science projects are judged individually on quality. If this is the case, citizen science has an important role in delivery and understanding of future marine policy, but is only one part of an integrated solution.