Importance of integrating mixoplankton into marine ecosystem policy and management-Examples from the Marine Strategy Framework Directive

Marine plankton capable of photosynthesis and predation ("mixoplankton") comprise up to 50% of protist plankton and include many harmful species. However, marine environmental management policies, including the European Union Marine Strategy Framework Directive (MSFD) and the USEPA, assume a strict dichotomy between autotrophic phytoplankton and heterotrophic zooplankton. Mixoplankton often differ significantly from these two categories in their response to environmental pressures and affect the marine environment in ways we are only beginning to understand. While the management policies may conceptually provide scope for incorporating mixoplankton, such action is rarely implemented. We suggest that the effectiveness of monitoring and management programs could benefit from explicit implementations regarding the ecological roles and impact of mixoplankton. Taking the MSFD as an example of marine management guidelines, we propose appropriate methods to explicitly include mixoplankton in monitoring and marine management. Integr Environ Assess Manag 2024;00:1-18. (c) 2024 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC). Mixoplankton (capable of photo- and heterotrophy) are a broad trophic group that is currently not considered by marine environmental management, while they often display different responses to environmental changes than strict phytoplankton or zooplankton due to their unique physiology. Many harmful algal species that are currently being monitored due to their impact on public health and the economy are mixoplankton, and effective forecasting systems may be challenging to establish by not considering their unique trophic mode. We showcase where the current omission of mixoplankton from marine management can misinform on the environmental status of marine ecosystems and how existing management and monitoring programs can benefit from including mixoplankton. Using the European Marine Strategy Framework Directive as an example, we show how mixoplankton can be integrated into existing management programs and where research gaps still exist.