Abstract:It is well know that bacteria play a crucial role in the cycling of energy and matter in aquatic systems; however, there is still a controversy on the mechanisms regulating bacterial production. Two major mechanisms for controlling bacterial production have been proposed, grazing by protozoans and availability of resources. Recent finding indicate that viral lysis is another key factor in the microbial food web. Grazing by predators (mainly nanoflagellates) and viral lysis are the 2 major know sources of mortality for bacterioplankton. On average, the 2 mechanisms seem to be responsible for an equal amount of bacterial mortality; however, the temporal and spatial variability of both are high. The East China Sea (ECS) is located on the western edge of the Northwest Pacific Ocean, and is characterized by dynamic interactions among water systems including nutrient enriched freshwater input from the Changjiang River. In addition to freshwater input from Changjiang River, there are three other water masses which influence the ECS: the Yellow Sea Coastal Water (YSCW) from north to south along the northwest coast of the sea, the Kuroshio Water (KW) coming from the western equatorial Pacific in the east and Taiwan Current Warm Water (TCWW) from the south. Until now, studies in oligotrophic waters have mainly focused on bacterial mortality due to nanoflagellate grazing. However, in eutrophic waters, such as Changjiang River plume, virus may be an important source of bacterial mortality. The contribution of viruses and nanoflagellate to bacterial mortality in ECS environments is still poorly understood. In this study, our main goal is to extensively apply the dilution method for comparative assessment of virus-induced and nanoflagellate grazing mortality of bacteria in different ECS ecosystems.