The allelopathic efficacy of aqueous extracts derived from Pyropia haitanensis on five species of bloom-forming microalgae: An environmentally viable approach to control harmful microalgal blooms.

Various methods have been used to control harmful algal blooms (HAB), including chemical and physical strategies, but their long-term ecological harm remains. As key ecosystem components, macroalgae like Pyropia haitanensis offer potential; we explore the antialgal effects of its water-soluble extracts on microalgal blooms. Initially, the inhibitory effects of water-soluble extracts from the residual biomass following methanol and ethanol extraction of dried P. haitanensis were evaluated against five bloom-forming microalgal species for 120 h. In comparison with methanol, the powder residue subsequent to ethanol extraction demonstrated greater effectiveness, indicating that numerous water-soluble compounds were extracted by methanol (ME), which was further fractionated for testing on microalgae. The pure water-soluble fraction obtained from the ME significantly impacted these strains; however, microalgal cells survived at lower densities even after 96 h of exposure. A GC-MS analysis identified 36 confirmed compounds in the aqueous extract phase. Notably, the water-soluble extracts effectively regulate microalgal growth without fully lysing cells, offering an eco-friendly strategy for managing HAB.