Effect of the Yellow Sea Cold Water Mass (YSCWM) on distribution of bacterioplankton

Four surveys were carried out in August 2001, and in August, September and October 2002 in the southern Yellow Sea, China. Bacterioplankton abundance and biomass were quantified along the transects from Qingdao, China to the Korean island of Jeju. In this paper, the author describes the distribution of bacterioplankton and predatory pressures, and also discusses the impact of Yellow Sea Cold Water Mass (YSCWM) on the distribution of bacterioplankton. The range of Synechococcus biomass was 0.78–33.49 mg C/m3 (on average 6.26 mg C/m3), and heterotrophic bacteria biomass was 1.58–21.25 mg C/m3 (on average 5.79 mg C/m3, n=197). In the vertical direction, the distribution order of Synechococcus biomass was mid-layer>surface>bottom, and the one of heterotrophic bacteria biomass was surface>mid-layer>bottom. The contribution of Synechococcus to the total phytoplankton biomass (SB/PB) ranged from 2% to 99% (on average 42.5%), and the ratio of heterotrophic bacterial biomass to phytoplankton biomass (HBB/PB) was from 5% to 637% (on average 85%). Daily variations of bacterioplankton biomass at anchor stations showed that the maximal Synechococcus biomass was 8.8 times the minimum, and it was 2.8 times in heterotrophic bacterial biomass. The distribution of bacterioplankton accorded with temperature and salinity, and the minimum of bacterioplankton biomass occurred in the YSCWM waters. At the same time, the microzooplankton (20–200 μm) preyed on Synechococcus in these waters, with the ingestion rate of about 0.20–0.42/d.