Mitigation of harmful algal bloom (Margalefidinium polykrikoides) intensity and toxicity via aeration processes

Given the significant ecological and economic threats harmful algal blooms (HABs) pose to coastal ecosystems and aquaculture, particularly those caused by the fish-killing dinoflagellate, Margalefidinium polykrikoides, effective mitigation strategies are urgently needed. HAB mitigation approaches can be chemical, biological, or physical, with the latter category including mechanical mixing and bubble injection. In this study, we systematically evaluated the effects of four physical treatment approaches-orbital shaking, nanobubble injection (with and without ozone impregnation), and macrobubble injection-on the growth, photosynthetic efficiency, and toxicity of wild and cultured populations of M. polykrikoides. Among the mitigation treatments tested, macrobubble injection was highly effective, significantly and consistently suppressing growth, reducing cell densities and photosynthetic efficiency, and reducing and, in some cases, completely eliminating fish mortality, even in cases where fish exposed to M. polykrikoides without bubbling experienced 100% mortality. During studies with bloom populations, macrobubble treatments consistently caused growth inhibition of M. polykrikoides while promoting the growth of co-occurring phytoplankton including Prorocentrum cordatum, highlighting the potential for macrobubbles to induce genus-level shifts in community composition. Collectively, these findings indicate that macrobubble injection is a promising non-chemical method for selectively mitigating M. polykrikoides blooms, offering a potential tool for integrated HAB management, especially in an aquaculture-setting.