Abstract:The species composition, density and seasonal variation of phytoplankton in Sanggou Bay were investigated in April, July and November, 2006 and January, 2007. There were 92 species belonging to 28 genera of phytoplankton collected during the surveys, which were mainly composed of diatoms (74 species) and dinoflagellates (11 species). Dominance index analysis indicated that diatoms were the predominant species. Shannon Wiener index of diversity ranged from 1.91 to 2.74 on seasonal average (Spring > Summer > Autumn > Winter). The phytoplankton densities and their distribution patterns varied in different seasons. The highest density was in winter (188.4×104 cells/m3 on average). The densities were 63.0×104 and 11.7×104 cells/m3 on average in spring and autumn, respectively. The lowest density was in summer (9.2×104 cells/m3 on average). For the horizontal distribution patterns, phytoplankton was more abundant in the coastal shallow waters of the bay in winter and summer, whereas the higher densities were found in the shellfish kelp mixed culture areas which located in the center of the bay. Compared to the historical data, the species quantity and density of the phytoplankton obviously declined in Sanggou Bay after more than 20 years' mariculture. The density of culture species and culture technology had significant influences on the quantity and seasonal distribution of phytoplankton.
