In Situ Enclosure Experiments Evaluating Clay–Bacillus Ba3 Broth for Dinoflagellate Control in Coastal Aquaculture Waters

We evaluated the algicidal properties of Bacillus Ba3 fermentation broth combined with clay for harmful algae bloom (HAB) control through in situ enclosure experiments in Suao Bay, China. It was indicated by the results that the combination significantly reduced HAB abundance, turbidity and phosphorous in water without affecting zooplankton and small fish. The treatment achieved 99.8% (Phase 1) and 100% (Phase 2, with sediment) removal rates for harmful dinoflagellates, primarily Prorocentrum donghaiense and Karenia mikimotoi, while demonstrating high taxonomic selectivity, allowing beneficial diatom populations such as Chaetoceros spp. to remain resilient. This synergy is attributed to clay acting as a physical carrier that brings adsorbed algicidal metabolites into direct, prolonged contact with algal membranes. This method shows promise for prolonged dinoflagellate control and may offer an economical and environmentally sound approach to HABs. More research is needed to establish its action on a wider scale in marine environments.