Phytoplankton community in the Bohai Sea and its relationship with environmental factors

A comprehensive survey was carried out in the Bohai Sea(37°00′-40°00′N, 118°00′-121°00′E)from November25thto December 1thin 2011. Phytoplankton species composition and abundance were studied by Uterm觟hl method, and the relationship between phytoplankton community and environmental factors was analyzed. A total of 65 taxa which belong to 30genera of 3 phyla were identified. The phytoplankton community was mainly composed of Bacillariophyta and Dinophyta,and there were also a few species belonging to Chrysophyta. Most of the ecotypes of phytoplankton species were neritic, and preponderant species were Paralia sulcata(Ehrenberg) Cleve, Coscinodiscus excentricus Ehrenberg, Ceratium fusus(Ehrenberg) Dujardin, Pleurosigma affine Grunow, Coscinodiscus asteromphalus Ehrenberg and Nitzschia sp., etc. Cell abundance ranged from 0.89 ×103to 16.4 ×103cells/L with an average of 4.36 ×103cells/L. Horizontally, the surface distribution of cell abundance in the survey area was dominated by diatoms, and the high value appeared in the areas to the south of the Liaodong Bay and to the west of the Bohai Strait. The high cell abundance of dinoflagellates mainly appeared in western and northwestern part of the survey area. In the vertical direction, phytoplankton cell abundance increased in the upper water, and then decreased in the bottom water. Both of Shannon-wiener diversity index and Pielou′s evenness index were higher in the central part of the survey area. By comparing the results with historical data, it can be inferred that the shift phytoplankton community of from diatom dominated community to diatom-dinoflagellate dominated community occurred in central Bohai Sea during the last 30 years. PCA and CCA analysis revealed that the change of nutrient structure in central Bohai Sea might be responsible for this community shift.