PHYTOPLANKTON COMMUNITY STRUCTURE IN THE CHANGJIANG ESTUARY AND ITS ADJACENT WATERS IN 2004

Data obtained in the Changjiang estuary and its adjacent waters during February, May, August, November in 2004 were analyzed for understanding the seasonal succession patterns of phytoplankton, and the relationship between the community structures and environmental factors. A total of 153 species were identified, among which 111 were diatom and 42 dinophytes. Compared with the data of 1985—1986, the abundance of dinophytes increased in spring, declined in summer, and slightly changed in fall and winter. The number of dinophytes species increased in spring, summer and fall. In 2004, the phytoplankton community was mainly comprised by temperate coastal species; tropic and widespread species appear more in frequency and abundance; Skeletonema costatum dominated in the estuary. The variation in phytoplankton abundance in 2004 stood out in spring with a single peak, different from 1985—1986. The diversity index of phytoplankton community in spring was slightly greater than that of 1986. Six assemblages of phytoplankton taxa were confined accord- ing to CCA ordination analysis, and were in possession of different responding styles to the environmental variables. In 2004, temperature, salinity, transparency, DO, TP, pH, NH+4 and PO ~(3-)4 were the main factors affecting the structure of phytoplankton community (P0.01). Since 1980’s, the environmental conditions had changed obviously: concentrations of SiO (~2)_3 , NO-3 and NO-2 nearly doubled that of 1985—1986, while NH4+ and DO decreased; and the temperature rose significantly. As a result, the structure of phytoplankton community changed too, and the factors driving the community variation were diverse during all seasons.