Pseudo-nitzschia bloom and its ecological role in the biological community in the Daya Bay, the South China Sea

Population densities of genus Pseudo-nitzschia,phytop lankton and zoop lankton were investigated daily from Apirl to May,2000,in the Daya Bay,the South China Sea,and relationships among these characteristics were also analyzed.The results show that at the beg inning of survery,species composition and densities of planktonic community were both rare followed by a rapidly increasing growth of Pseudo-nitzschia with a highest density of 2.93×10⁵ cells/dm³ which have reachecd the bloom density.P.pseudodelicatissmia and P.pungens were the joint-causative species as well as species composition and densities of diatom and dinoflag llate enriched during the bloom.It was found that Pseudo-nitzschia became the most miportant component in the spirng diatom bloom due to its advantage in the competition among the different species.The effect of zoop lankton's (especially copepods) down-control on Pseudo-nitzschia was't obviously mostly because of the less grazing pressure.The reasons mentioned above made Pseudo-nitzschia abundant and it a potential bloom-causing species in the study area.