GlobalHAB’s research indicates that the potential positive and negative interactions among HAB species mediated by different allelochemicals play important roles in the biological adaptations of HAB species (GlobalHAB, 2017). As the dominant class of coastal algal blooms, diatoms respond to biotic and abiotic unfavorable factors by producing allelopathic oxylipins including polyunsaturated aldehydes (PUA), which are the enzyme-catalyzed oxidation products of membrane lipids. Many oxylipins are known to affect marine microorganisms over various trophic levels, from zooplankton grazers to phytoplankton competitors and bacteria decomposers, which strengthens their potential importance in natural bloom environments (Wu et al., 2016, 2021). 
    Coastal eutrophication drives the intense algal blooms outside the Pearl River Estuary (PRE) with the predominant species being oxylipin-rich diatoms. We conducted field research to investigate the roles of oxylipins produced by diatom along with algal bloom dynamics in coastal waters of the PRE. Allelochemical oxylipins produced by diatoms might extend the coastal algal blooms, which could potentially affect the marine food web health and the coastal carbon cycle. We also found elevated concentrations of biogenic PUA associated with the hypoxic waters in the nearshore of the PRE. The biogenic particle-adsorbed PUA (micromolar level) retrieved from hypoxic waters has been demonstrated to have the potential to affect the abundance, metabolic activity, and community composition of particle-attached bacteria. The changes in bacteria structure and metabolism could lead to an increase in oxygen consumption during the process of particulate organic matter degradation and may contribute to the formation of coastal hypoxia. The underlying molecular mechanism of PUA-dependent allelopathic function of algae-bacteria interactions is becoming an important hotspot for future HAB studies.