Phytoplankton community in the northern area of South China Sea in summer of 2009

In this paper,phytoplankton samples were taken from the northern area of South China Sea(18°~22°N,110°~117°E) in August 2009,and the phytoplankton species composition,community structure,diversity and its spatial distribution were reported.A total of 5 phyla 60 genera and 109 taxa were identified according the Uterm hl method in the survey area.And the major groups were diatom and dinoflagellate.Most of the phytoplankton ecotypes were temperate coastal species,while the warm-water species and oceanic species were rarely presented.The dominant species in the survey area were Pseudo-nitzschia delicatissma,Thalassionema nitzschioides,Melosira grannulata,Pseudo-nitzschia pungens,Detonula pumila,Protoperidinium sp.,and Asterionopsis glacialis.The cell abundance of phytoplankton ranged from 0.009×103 to 249.930×103cell/L,with an average of 8.197×103cell/L.The highest cell abundance in surface layer was found in the Pearl River Estuary and southern part of the survey area.The high cell abundance of dinoflagellates was found in the coastal seawater of Guangdong Province.Vertically,the phytoplankton cell abundance were concentrated in surface water and decreased rapidly down to the bottom.The low values of Shannon-Wiener index and Pielou’s evenness index were found in the southern Pearl River Estuary and the coastal water of Guangdong Province,indicating the rapid development of phytoplankton community.