Study On Phytoplankton Community Structure In Western Waters Of Liaodong Bay

By means of net tow and water collecting combination, the species composition, distribution of cell abundance, dominant species, community diversity and seasonal variation of phytoplankton were analysed, using the data obtained during the investigation at 25 grid stations and 2 consecutive stations in the western sea of Liaodong Bay in May (spring), August (summer), October (autumn) and December (winter) 2009. Water samples are analyzed by Uterm?ll methods commonly used in international.This study provides basic data for further research of ecological character in the survey area.A total of 172 species which belong to 70 genera of 3 phyla were identified from 4 cruises in 2009, including Bacillariophyta (58 genera and 145 species), Pyrrophyta (11 genera and 25 species), Chrysophyta (1 genera and 1 species) .there was also 1 species of Ebria tripartita which systematic status was undertermined. The main phytoplankton community was Diatoms in which Chaetoceros and Cosinodisus are more than others species.while Protoperidinium is the most species in Pyrrophyta. The maximum quantity of species appeared in autumn and the minimum quantity was in spring.The cell abundance of phytoplankton was mainly determined by the distribution of Bacillariophyta and its peak located at the mouth of Liugu River and northeast of the investigated sea area (pollution outlet) .The cell abundance of net-Pyrrophyta was 20.91×10~4 cells/m~3 and took up a percentage of 58.65 in total cell abundance. The monitoring of Pyrrophyta in spring should be strengthen.The cell abundance of phytoplankton ranged from 0.80 to 56.38×10~6 cells/m~3 with an average of 16.42×10~6 cells/m~3 during the year. ; The cell abundance of net-phytoplankton ranged from 0.48 to 76.60×10~4 cells/m3 with an average of 34.09×10~4cells/m~3. The results showed a seasonal succession rule characterized by two cell quantity peaks in the spring and autumn. The cell abundance of phytoplankton in surface water showed a strong negative correlation with salinity and a strong positive correlation with temperature in spring while a strong positive correlation with temperature as well as reactive phosphate in autumn. There is a strong negative correlation between the net-phytoplankton cell abundance and salinity.The cell abundance of phytoplankton fluctuated between day and night. The higher cell abundance of water samples appears generally in nighttime in autumn and winter, which was opposite in spring and summer. The peak cell abundance of net-phytoplankton appears in the afternoon in autumn and winter, and it appears at nighttime in summer.The dominant species were changed during four seasons. Chaetoceres curvisetus, Noctiluca scintillans, Skeletonema sp., Proboscia alata, Cylindrotheca elaterium, Coscinodiscus gigas were the dominant species in spring; Paralia sulcata, Coscinodiscus spp., Nitzschia spp., Chaetoceros lorenzianus, Helicotheca tamesis, Pleurosigma spp. in summer; Chaetoceres curvisetus, Coscinodiscus spp., Paralia sulcata, Chaetoceros soccialis, Ditylum sol, Odontella sinensis in autumn; Paralia sulcata, Coscinodiscus spp., Noctiluca scintillans, Coscinodiscus wailesii, Ditylum sol, Pinnularia spp. in winter. The common dominant species in spring, summer, autumn and winter were Paralia sulcata and Coscinodiscus spp.; the common dominant species in summer, autumn and winter was Nitzschia spp.. The ecotype of main dominant species were mainly temperate and neritic or widespread species.The Shannon-Wiener index ranged from 1.80 to 3.43 with an average of 2.33 during four cruises. The peak of diversity index occurd in winter and the average was 2.53, the low period occurd in spring and the average was 1.94. The Pielou evenness index ranged from 0.42 to 0.90 with an average of 0.70 during the year. The peak of evenness index occurd in summer, the average was 0.85. The low period of evenness index occurd in spring, the average was 0.55. The Pielou evenness index ranged from1.40 to 10.14 with an average of 2.84 during four seasons. The peak of Margalef index occurd in summer and the average was 4.42; the low period occurd in spring and the average was 2.16. The Pielou evenness index and species richness showed high value in summer. It appeared that the community structure in summer was better than that in other seasons. The Shannon-Wiener index,the Pielou evenness index and the Pielou evenness index were lower in spring.