Plankton community responses to pulsed upwelling events in the southern Taiwan Strait

We used field observations (mapping and time-series observations) and satellite data to investigate the changes of environmental factors and plankton community structure during four pulsed upwelling events in the southern Taiwan Strait (STWS) during August 2004 and July 2005. Based on the surface temperature, salinity, and concentrations of nitrate, oxygen, and chlorophyll a (Chl a), we identified three stages of upwelling: recent, mature, and aged upwelled water. Diatoms and Synechococcus dominated during the first two and third stages of the upwelling, respectively. In recently upwelled water, phytoplankton grew rapidly, and nutrient concentrations were relatively high. Diatoms accounted for >69% of the total Chl a in recently upwelled and mature water. As the upwelled water aged, the phytoplankton community shifted to coexistence of diatoms and Synechococcus. The microzooplankton community was dominated by aloricate ciliates and tintinnids during upwelling, but the abundance of heterotrophic dinoflagellates increased as the upwelled water matured. Microzooplankton grazing reached a maximum during the mature stage and approximately balanced phytoplankton growth in aged, upwelled water. Overall, our study revealed rapid changes in the plankton community during the different stages of upwelling that reflected the complex and dynamic nature of upwelling systems.