Abstract Ecosystem-based management and conservation approaches such as marine protected areas (MPAs) require large amounts of ecological data to be implemented and adaptively managed. Recently, many citizen science programs have endeavored to help provide these much-needed data. Implementation of MPAs under the Marine Life Protection Act (MLPA) Initiative in Southern California was followed by a monitoring program to establish a comprehensive baseline of the ecological conditions of several marine ecosystems at the time of MPA implementation. This baseline monitoring consortium involved several citizen science monitoring programs alongside more traditional academic monitoring programs, creating an opportunity to evaluate the potential for citizen scientists to become more involved in future long-term monitoring efforts. We investigated different citizen science models, their program goals, and contributions to MPA baseline monitoring, including their respective monitoring protocols and data quality assurance measures, in the context of the goals of the MLPA baseline monitoring program. We focused on three very different case studies: (i) commercial fishermen and other volunteers collaborating with researchers to study the California spiny lobster, (ii) volunteer divers monitoring rocky reefs with the Reef Check California (RCCA) program and (iii) middle and high school students monitoring the inter-tidal life of rocky shore and sandy beach ecosystems with the National Marine Sanctuaries’ Long-term Monitoring Program and Experiential Training for Students (LiMPETS) program. We elucidate capacities and potential of citizen science approaches for MPA baseline monitoring and for building capacity towards sustainable long-term monitoring of MPAs. Results from this study will be relevant and timely as the monitoring of California's MPAs transitions from baseline to long-term monitoring, and as citizen science continues to become more prevalent in California and elsewhere.