Ecological Study On Phytoplankton Assemblage In Changjiang River Estuary And Its Adjacent Waters

The characteristics of phytoplankton assemblage in Changjiang River estuary and its adjacent waters from summer 2004 to spring 2005 are studied in this paper including species composition, dominant species, cell abundance, community diversity, spatial and temporal distribution, seasonal variation and their relationships with the marine environments. The purpose of this study is to recognize the influence that the environment emphasizes on the phytoplankton and the indicating functions that the different phytoplankton species have. Besides, providing fundamental data to the problem of eutrophication and estuary ecosystem protection research.The Changjiang River estuary lies in the temperate zone which has four seasons each year. There are seasonal dynamics in solar radioactive and temperature. The runoff of the river varies between summer and winter which causes the changes in salinity and trophic salts. The annual precipitation in each spring supplements the nutrient concentration. Phytoplankton species have different adaptation strategies and interspecies relationships. Concerned all above, the phytoplankton community in this area appears the phenomenon of seasonal variation.The results show that total phytoplankton species richness is 165. Of them 54 genus 114 taxa are found in Bacillariophyta, 17 genus 40 taxa in Pyrrophyta, 2 genus 4 taxa in Chlorophyta, 3 genus 4 taxa in Chrysophyta and 3 genus 3 taxa in Cyanophyta. Diatoms and dinoflagellates are the main phytoplankton groups in the study area. The phytoplankton ecotypes are more in temperate near shore species, warm water species and oceanic species are rarely appearing. The dominant species are Skeletonema costatum, Proboscia alata f. gracillima and Pseudo-nitzschia pungens in summer; Skeletonema costatum, Paralia sulcata and Thalassionema nitzschioides in autumn; Paralia sulcata and Skeletonema costatum in winter; Karenia mikimotoi, Skeletonema costatum and Prorocentrum dentatum in spring. The cell abundance varies between seasons with the maximum 361.81×103 cells/L appearing in spring and 57.84×103 cells/L in summer. Distinctive Shannon-Wiener diversity index and evenness index are found in different seasons with the optimum appearing in autumn. The maximum species richness appears in summer phytoplankton assemblage.The relationship between the phytoplankton and environments indicates that the Pearson correlation between nitrates and phytoplankton species are significant in all four seasons. The nitrate, silicate and salinity are the main factors among the environments, which control the phytoplankton distribution during the four cruises. The different distribution pattern shows the different adaptation strategies in phytoplankton species. More field experiments need to be done because of the complex marine environment dynamics and large scale variation in spatial and temporal distribution of phytoplankton assemblage.