Study On Phytoplankton Community Structure In Offshore Water Of South Qingdao

According to the investigation in offshore water of South Qingdao in August (summer) and December (winter) 2006, April (spring) and October (autumn) 2007, the species composition, distribution of cell abundance, dominant species and their distribution, community diversity and community structure seasonal variation of phytoplankton were analyzed. This study provides basic data for further research of ecological character in the survey area. Sampling methods include net tow and water collecting for qualitative and quantitative study.A total of 185 species which belong to 75 genera of 3 phyla were identified from 4 cruises, including Bacillariophyta ( 153 species ) , Pyrrophyta (29 species ) , Chrysophyta(3 species). The cell abundance of phytoplankton range from 2.67 to 253.50×10~5cells/m~3 with an average of 40.54×10~5cells/m~3 during the year. The cell abundance of diatom range from 0.80 to 242.33×10~5cells/m~3 with an average of 35.93×10~5cells/m~3 and take a percentage of 88.63 in total cell abundance. The cell abundance of diatom range from 0 to 77.90×10~5cells/m~3 with an average of 3.50×10~5cells/m~3 and take a percentage of 8.63 in total cell abundance. Diatom is the dominant in cell abundance and species richness.The maximum of percentage in cell abundance of diatom is in autumn and dinoflagellate is in summer. The peak of cell abundance is in autumn, the second peak occurs in summer and the low period is in spring. The maximum of species richness is also in autumn. There was a positive correlation between cell abundance and the depth(P<0.01) in spring. The reason of this phenomenon is that benthic diatom is the dominant group of phytoplankton in spring and they mainly appear in bottom water.The dominant species were Chaetoceres curvisetus, Ceratium fusus, Chaetoceres affinis, Coscinodiscus oculus-iridis, Dictyocha fibula and Skeletonema costatum in summer, Bacillaria paxillifera, Cyclotella spp, Pleurosigma spp, Nitzschia spp, Coscinodiscus oculus-iridis, Ceratium furca in winter, Navicula spp, Pinnularia spp, Bacillaria paxillifera, Pleurosigma spp, Noctiluca scintillans, Nitzschia lorenziana in spring and Rhizosolenia styliformis, Bacillaria paxillifera, Rhizosolenia imbricate, Ceratium fusus, Pleurosigma spp, Paralia sulcata in autumn. The dominant species show seasonal variation apparently.The Shannon-Wiener index range from 0.87 to 4.52 with an average of 3.08 during four cruises. The peak of diversity index occurs in autumn and the average is 3.25, the low period occurs in summer and the average is 2.81. The Pielou evenness index range from 0.28 to 0.97 with an average of 0.80 during the year. The peak of evenness index occurs in both winter and spring, the average is 0.86. The low period of evenness index occurs in summer, the average is 0.71. The Margalef index range from 0.38 to 2.51 with an average of 1.37 during four seasons. The peak of Margalef index occurs in autumn and the average is 1.64, the low period occurs in winter and the average is 1.19. The evenness and species richness show high value in autumn. It appears that the community structure in autumn is better than that in other seasons. The evenness in winter and summer are better than autumn while the species richness is not good enough.Net-phytoplankton cell abundance shows obviously less than water samples. This study found that the net-phytoplankton cell abundance of offshore water of South Qingdao was higher than the result of the Yellow Sea, and was lower compared with the data of Jiaozhou Bay.