Responses of Picoplankton to Nutrient Perturbation in the South China Sea, with Special Reference to the Coast-wards Distribution of Prochlorococcus Synechococcus and Prochlorococcus growth and mortality rates in the northern China Sea: range of variations and correlation with environmental factors Distribution Pattern of Photosynthetic Picoplankton and Heterotrophic Bacteria in the Northern South China Sea