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

摘要

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.