Abstract: Apparent global increase of harmful algal blooms (HABs) has been observed recently. Coastal eutrophication, longterm change of hydrological and meteorological parameters, as well as the adaptive and competitive strategies of HAB causative species, can affect the occurrence of HABs. Through producing toxins or high biomass, the HAB causative species pose potent threats on the health of humanbeings, mariculture industry and natural ecosystems. It's necessary to develop HAB prevention and control measures to mitigate the impacts of HABs. In China, an increasing trend of both scale and impacts of HABs has been found over the last two decades. More and more toxic algal blooms are recorded. The succession pattern of major HAB causative species, and the potential impacts, should be given more attention.

Key words: harmful algal bloom, eutrophication, mechanism, impact