Allelopathy in aquatic ecosystems: mechanisms, ecological roles, and implications for harmful algal blooms

Allelopathy is increasingly recognized as a key driver of species interactions in aquatic ecosystems, yet its ecological scope and functional significance remain insufficiently integrated. This review synthesizes current knowledge on chemically mediated interactions, emphasizing their ecological importance and potential role in mitigating harmful algal blooms (HABs). Growing evidence suggests that allelochemicals may represent environmentally sustainable alternatives to synthetic algicides, while the influence of allelopathy extends far beyond bloom control to encompass complex interactions among vascular plants, algae, cyanobacteria, diatoms, macroalgae, and corals. Aquatic allelopathy remains far less explored than its terrestrial counterpart, revealing substantial knowledge gaps and the need for ecologically realistic research frameworks. Both abiotic factors (e.g., light, temperature, nutrient availability) and biotic interactions strongly modulate allelopathic outcomes, highlighting the context-dependent nature of these processes. Particular attention is given to bloom-forming taxa such as Microcystis aeruginosa and Prymnesium parvum, which serve as model systems for understanding the relationship between toxicity and allelopathy. Evidence from dinoflagellates, diatoms, and other microalgae further underscores the mechanistic diversity of allelopathic interactions. By integrating findings across taxa and environments, this review advances a comparative framework for interpreting chemically mediated interactions in aquatic systems and identifies key priorities for future research. Collectively, the evidence positions allelopathy as both a fundamental ecological process and a promising avenue for the development of sustainable HAB management strategies.