During the warm seasons, quite low diatom concentrations occurred in the YSCWM area. During the August cruise, the average concentration and relative abundance of diatoms in the central area were only 0.05 mg m-3 and 30%, when the YSCWM prevailed. However, significantly higher concentrations of cyanobacteria were observed in August and south of the study area during the October cruise, associated with the higher temperature. Therefore, the dominance of diatoms was replaced by that of cyanobacteria (36 +- 16%, n = 7) in the central area. During October, when the YSCWM was decaying, the concentrations of chrysophytes and prasinophytes increased. And they contributed 38 and 18% of the Chl a biomass in the water column of the central yellow sea. In addition, the ratios of 19’-hexanoyloxfucoxanthin and zeaxanthin to Chl a during the warm seasons were relatively higher than those in the cold seasons.