An international team of experts, co-led by NOAA’s National Centers for Coastal Ocean Science (NCCOS) published a new review in Harmful Algae examining the limited number of marine Harmful Algal Bloom (HAB) control strategies that have been tested in mesocosms—large water enclosures used for controlled experiments—or in field trials. The review describes several reasons why progress in developing marine HAB control tools has lagged behind efforts focused on controlling blooms in freshwater systems.
As marine HABs increasingly threaten human health, seafood safety, tourism, and coastal ecosystems globally, there is a growing need for effective and scalable marine HAB control methods. The authors outline key challenges that have slowed progress and offer recommendations for the regulatory support, targeted research, investments, and public outreach needed to accelerate the availability of viable marine HAB control solutions. These improvements are essential for protecting marine resources and helping communities maintain safe access to seafood, beaches, and coastal waters.
Bottom: Method for HAB control using MC. At the surface, the clay/PAC mixture is sprayed as a slurry over the water surface, where flocs form between positively charged clay particles and negatively charged HAB cells. As these flocs settle, polymer chains linking floc particles act as a net and sweep capture additional HAB cells lower in the water column. The flocculated materials are then deposited on the sediment surface. (Figure 6 & 12 in Anderson et al., 2025).
The review presents a framework for evaluating whether a HAB control method is ready for real-world testing by weighing scientific, practical, and societal considerations against the risk of inaction. It also describes a phased, precautionary process that advances only the most promising control strategies from laboratory studies to controlled outdoor testing and ultimately, to full-scale deployments. The paper outlines the categories of HAB control—biological, chemical, and physical—and highlights several illustrative case studies. These include two promising NOAA NCCOS-supported approaches being tested for Karenia brevis control applications: DinoSHIELD, a naturally derived bacteria-based method (biological), and modified clay flocculation (physical).
The team presents actionable recommendations to speed progress in marine HAB control and help make solutions readily available to communities, businesses, and governments. They emphasize the importance of focusing on situations where the costs of inaction are high and mitigation efforts are most likely to be effective. This review highlights the importance of supporting social and economic research to better describe HAB impacts, evaluate the costs and benefits of different interventions, and strengthen public and stakeholder engagement in HAB control projects.
The review outlines several strategies to help develop and test promising HAB marine control approaches. These include expanding national and international testing and data sharing among the marine and freshwater HAB communities, partnering with engineers, encouraging private sector participation, streamlining regulations for field testing, and supporting programs such as the US HAB-Control Technologies Incubator to identify and rapidly test new ideas. The researchers emphasize the need for increased investment in HAB control research at national and regional levels.
Impacts of marine HABs are increasingly affecting coastal communities and marine ecosystems throughout the world, particularly where blooms disrupt seafood, tourism, recreation and other important marine resources. As these impacts continue to grow, so too will the demand for effective and scalable marine HAB control solutions. The review provides a roadmap to help nations develop and explore a range of viable marine HAB control approaches to better protect public health, support coastal economies, and sustain marine ecosystems worldwide.
The paper was presented on behalf of all co-authors by Dr. Vera Trainer, University of Washington at the 21st International Conference on Harmful Algae in Punta Arenas, Chile in October 2025.
NOAA is authorized to advance scientific understanding and assessment of HAB events through the Harmful Algal Bloom and Hypoxia Research and Control Act (33 U.S.C. §§ 4001 et seq.).
Citation: Anderson, D. M., Wells, M. L., Trainer, V. L., Suddleson, M., Claridge, K., Coyne, K. J., Dortch, Q., Gobler, C. J., Heil, C. A., Inaba, N., Laughinghouse, H. D., Mardones, J. I., Nakayama, N., Park, T., Peacock, M. B., Pokrzywinski, K., Raymond, H., Toyoda, J. H., Trethewey, D., Visser, P. M., Wang, Y., & Yuan, Y. (2025). Controlling harmful algal blooms (HABs) in marine waters: Review of current status and future prospects. Harmful Algae, 150, Article 102989. https://doi.org/10.1016/j.hal.2025.102989