Distribution and environmental impact factors of picoplankton in Changjiang River Estuary and its adjacent sea areas in autumn of 2006

In October 2006,an autumn cruise was conducted in the adjacent sea areas of Changjiang River Estuary to investigate the abundance,carbon biomass and distribution of picoplankton(Pico) and their relationship with environmental factors.Three groups of picoplankton,that is,Synechococcus(SYN),picoeukaryotes(PEUK) and heterotrophic bacteria(HBAC) were identified.The results show that the average abundance of SYN,PEUK and HBAC was(29.5±35.1)×103 cells/cm3,(0.9±0.6)×103 cells/cm3 and(7.6±4.3)×105 cells/cm3,and the mean carbon biomass was(5.2±6.1) mg/m3,(1.4±0.9) mg/m3 and(15.2±8.6) mg/m3 respectively.The cell abundance of each group showed different distribution characteristics.As for horizontal distribution,the abundance of SYN was low nearshore and high offshore with the high value at the east and southeast areas off the estuary,and that of PEUK was similar to SYN with the high value at the southern part of the study area.The high value of HBAC appeared in the northern area off the estuary.And for the vertical direction,they were evenly distributed in nearshore waters.Their subsurface abundance maximum occurred in offshore waters with that for SYN at the bottom of euphotic layer,while that for PEUK and HBAC at the surface or bottom of euphotic layer.The results of environmental factor correlation analysis showed that there was a distinct positive correlation between picoplankton carbon biomass and water temperature,and a close negative correlation between picoplankton and nutrients,total suspended materials and particle organic carbon.