SUMMER PHYTOPLANKTON COMMUNITY IN THE BEIBU GULF

Phytoplankton samples were taken from the Beibu Gulf(18°N~22°N,107°E~110°E) in August,2009.The phytoplankton species composition,community structure,and its spatial distribution were reported.A total of 4 phyla 60 genera and 90 taxa were identified according the Uterm hl method in the survey area.The major groups were diatom and dinoflagellate.Most of the phytoplankton ecotype was temperate coastal species,while the warm-water species and oceanic species were rarely presented.The dominant species in the survey area were Thalassionema nitzschioides,Chaetoceros sp.,Pseudo-nitzschia pungens,Guinardia flaccida,and Trichodesmium thiebaultii.The cell abundance of phytoplankton ranged from 0.330 to 19.765×103cell/L,with an average of 4.677×103 cell/L.The phytoplankton cell abundance reduced from coastal area to the center.Vertically,the phytoplankton cell abundances were concentrated in surface water and decreased rapidly down to the bottom.The Shannon-Wiener index and Pielou's evenness index were low in the coastal area of the survey area,which indicated the community structure of phytoplankton was unstable.