Phytoplankton growth and microzooplankton grazing in a subtropical coastal upwelling system in the Taiwan Strait

Phytoplankton growth and microzooplankton grazing were measured in a coastal upwelling system in the southern Taiwan Strait during the summers of 2004–2007, with emphasis on a comparison between upwelling and non-upwelling areas. Diatoms significantly dominated the phytoplankton community (49–92%, by pigment content) in the coastal upwelling area, while the prevailing groups varied, with Cyanophyceae, Chlorophyceae and diatoms, in the different stations of the non-upwelling area. Aloricate ciliates and tintinnids dominated the microzooplankton community, and there was a higher abundance of microzooplankton in the coastal upwelling area (1869 ind L−1), while there was lower abundance in the non-upwelling area (544 ind L−1). The phytoplankton growth rate in the upwelling area (1.02±0.27 d−1) was significantly higher than that in the non-upwelling area (0.51±0.05 d−1) (p<0.05), while the microzooplankton grazing rate in the upwelling area (0.85±0.37 d−1) was only a little higher than that in the non-upwelling area (0.50±0.17 d−1). Growth (synthesis) rates were similar among the four representative pigments, while grazing (destruction) rates were higher for 19′-hexanoyloxyfucoxanthin than those for fucoxanthin, zeaxanthin and divinyl chlorophyll a. In addition, there was almost a balance between phytoplankton growth and microzooplankton grazing in the non-upwelling area, while phytoplankton growth was higher than grazing in most cases in the upwelling area.