Communitystructure of net-phytoplankton in the northwest South China Sea in the summer of 2012

Net-phytoplankton community structure and abundance were preliminary studied on the basis of investigation in the northwest South China Sea from August to September,2012.A total of 206 species were identified,belonging to 4phyla with 55 genera,of which 55.3% were Bacillariophyta(40genera and 114species)and 41.7% were Pyrrophyta(10 genera and 86 species).The average cell abundance of phytoplankton was 66.67×104cells·m-3,which was mainly contributed by diatom with mean value of 65.79×104cells·m-3.The mean value of dinoflagellates was only 0.88×104cells·m-3.The dominant species were diatom such as Thalassionema franenfeldii,Rhizosolenia alata and Thalassionema nizschioide.The average Shannon-Wiener diversity index of phytoplankton community was 2.67,and the high value occurred in the Xisha Islands and the east part of surveyed area.Distributive pattern of phytoplankton was much related with environmental condition.The water column with high phytoplankton abundance and species diversity often coincided with a high nutrient level particularly in upwelling zone.It suggests that nutrient may play important role in impacting the distribution of phytoplankton abundance and the community structure in this region.