Seasonal Changes In The Phytoplankton Community And Experimental Ecology Of Scrippsiella Trochoidea In Daya Bay, South China Sea

The study of the phytoplankton ecology and environmental factors in Dapengao, Daya Bay was carried out from April 2005 to April 2006. Furthermore, the growth and cyst formation, germination of Scrippsiella trochoidea were investigated under different environmental conditions, by a series of indoor experiments.A total of algal 160 taxa were identified. The total cell densities of phytoplankton ranged from 0.04×10~4cells/L to 1778.12×10~4cells/L. Diatom was the predominant group of phytoplankton, which contributed 93.49% of the total cell numbers, while dinoflagellates only held 2.33%. Diatoms were present throughout the whole year, and species such as Skeletonema spp., Pseudo-Nitzschia spp., dominated alternately. Dinoflagellates occurred more frequently and abundantly in spring and winter when water temperature was below 25℃, and dominant species were Prorocentrum spp., Scrippsiella spp., Alexandrium spp.There were two abundance peaks of phytoplankton throughout the whole year, one was in summer and the other was in late winter. Because of good exhanges of water and richness of nutrient, the phytoplankton density was higher in shellfish aquacultural area than fishery area. The cell densities were positive correlation with temperature and DIN datas. Shannon-weaver species diversity index (1.43) and evenness index (0.32) were much lower, which suggested that the dominance of a few species would greatly change the community composition of phytoplankton.The indoor experiments showed growth of 5. trochoidea was strongly inhibited by nutrient inhibition, more significantly by P limitation. Encystments occurred at the beginning of the stationary phase under high nutrient concentrations, while cysts were observed early under nutrient limitation. Nitrogen depletion enhanced the cyst formation, and the highest encystment rate, nearly close to 80% under the condition of moderate N depletion. The mandatory dormancy period was from 15 d to 25 d, and was extended under low temperature. The cumulative excystment rates was about 60-80%, showed little difference among temperatures. Low temperature (4℃) storage...