The Spatial And Temporal Distribution Of Picophytoplankton In Bohai Sea

Picophytoplankton is defined as the phytoplankton ranging from0.22to2μm,including Prochlorococcus （Pro）, Synechococcus （Syn） and picoeukaryotes （Euk）.They are abundant and widespread in the ocean all over the world and playing animportant role in the organic material cycling. The Bohai Sea, one of the inland seasin China, is connected with the Yellow Sea through the Bohai Strait. It is one of theimportant areas for marine ecological research. The characteristics of the abundanceand distribution of picophytoplankton in four transects including Bohai Strait transect,Liaodong Bay transect, Bohai Bay transect, Laizhou Bay transect were investigatedby flow cytometry in four seasons. The samples were gathered from April2010toNovember2011from70stations in the Bohai Sea.Syn and Euk had rich quantities, while Pro was not detected. In the Bohai Straittransect, the value of picophytoplankton abundance was low in summer and autumn,and high in spring and autumn. In the Liaodong Bay transect, the value of Syn andEuk abundance of the westen area （the Qinhuangdao offshore） were higher in summerand lower in other three seasons. In the Baihai Bay transect, the abundance of Synwas higher in summer and lower in other three seasons in the southern area （near theYellow River Estuary）, in which the abundance of Euk was lower in four seasons. Inthe Laizhou Bay transect, the abundance of Syn in the eastern area （the Longkou Portoffshore） was higher in summer and autumn, while it was lower in winter. Theabundance of Euk was similar as the distribution of Syn in autumn and in winter, andit was lower in the eastern area in summer.The average value of Syn abundance was6.45×10²cells mL^-1in spring,5.31×10⁴cells mL^-1in summer,1.38×10⁴cells mL^-1in autumn, and7.61×10²cells mL^-1inwinter. The abundance value of Syn showed no obvious difference between springand winter, but significant difference among other seasons. It decreased with seasonsin sequence of autumn, summer, spring/winter. In winter, the diel variation trend of Syn abundance in the continuous stations was much the same in surface and bottomlayer of water, and showed two peaks in4:00and13:00, respectively.The average value of Euk abundance was2.80×103cells mL^-1in spring,5.17×103cells mL^-1in summer,7.20×103cells mL^-1in autumn, and3.95×10²cells mL^-1inwinter. The abundance of Euk showed no obvious difference between summer andautumn, but significant difference among other seasons. It decreased with seasons insequence of summer/autumn, spring, winter. In winter, the diel variation trend of Eukabundance in the continuous stations was much the same in surface and bottom layerof water, and showed two peaks at4:00and13:00, respectively.The abundance of Syn was positively correlated with salinity in spring andpositively correlated with temperature in summer by correlation analysis. It showedobviously positive correlation with Euk, heterotrophic bacteria and virioplankton inautumn. The abundance of Euk was positively correlated with temperature andsalinity in four seasons, and had obviously positive correlation with heterotrophicbacteria and virioplankton in summer and autumn.