The Yellow Sea Cold Water Mass (YSCWM) is very important phenomena in the southern Yellow Sea, especially prominent in summer and autumn. It is renewal in winter every year and the boundary and temperaturesalinity structure remain almost unchanged one year comparing to another. The primary characters of YSCWM are low temperature with a remarkable variation (5～12℃) and a rather constant salinity (31.5～32.5). The particular physicochemical parameters of YSCWM represent a very attractive model system to study the impact of environmental changes on the biomass of bacterioplankton which is composed mainly of heterotrophic bacteria and two types of photosynthetic prokaryotes cyanobacteria, Prochlorococcus and Synechococcus. These prokaryotes are basic components of microbial loop, and play an important role in the marine food web.
In this paper, the author described the distribution of bacterioplankton and the preying pressure. At the same time, the author discussed the effect of Yellow Sea Cold Water Mass (YSCWM) on the distribution of bacterioplankton.
Four special surveys were carried out in Aug. 2001, and Aug., Sep., Oct. 2002 in the southern Yellow Sea, China. Bacterioplankton abundance and biomass were quantified along the transect from Qingdao of China to Jeju island of Korea. Samples for bacterioplankton were collected from a SeaBird CTD-General Oceanic Rosette assembly with 10 l Go-Flo bottles, and preserved with buffered glutaraldehyde at a concentration of 1%. Synechococcus cyanobacteria abundance was determined by directly counting cell numbers using epifluorescence microscopy method; and heterotrophic bacteria after acridine organge staining. The biomass of Synechococcus cyanobacteria and heterotrophic bacteria were calculated with a carbon conversion factor of 294 fg/cell and 20 fg/cell, respectively. Concentrations of Chl-a were measured on a Turner fluorometer. Phytoplankton biomass was calculated by a conversion factor of 50 mg C/mg chlorophyll.The results showed: the rang of Synechococcus biomass was 0.78～33.49 mg C/m³ (average was 6.26 mg C/m³), and heterotrophic bacteria biomass was 1.58～21.25 mg C/m³ (average was 5.79 mg C/m3, n=197). In the vertical direction, the distribution of Synechococcus biomass was shown as the mid-layer>surface>bottom, and heterotrophic bacteria biomass was surface>midlayer>bottom. The contribution of Synechococcus to the total phytoplankton biomass (CB/PB) was from 2% to 99% (average vaule was 42.5%), but the ratio of heterotrophic bacteria biomass to phytoplankton biomass was from 0.05 to 6.37 (average vaule was 0.85). Daily variations of bacterioplankton biomass at anchor stations showed the Synechococcus maximal biomass was 8.8 times of the minimum value, and 2.8 times of heterotrophic bacteria. All in a word, the distribution of bacterioplankton was accorded with temperature and salinity, the minimum value of bacterioplankton biomass occurred in YSCWM waters. At same time, the microzooplankton (20～200 μm) were the grazer who prey on Synechococcus in this waters, and the ingesting rate was about 0.20～0.42/d.