Spatial Variability in Summer Phytoplankton Community from Offshore to Coastal Surface Waters of the Northwestern South China Sea

Results are mainly presented about the spatial changes in phytoplankton chlorophyll a(chl a) concentration, community structure and picoplankton abundance(i.e. Synechococcus and picoeucaryotes) from offshore to coastal surface waters of the South China Sea in the summer period of 2013. Total chl a concentration increased from 0.024 to 19.1 μg·L~(-1) from offshore to coastal waters. Coinciding well with chl a, the proportion of microplankton(20 μm) increased from 6.0%-81%, while that of picoplankton(3 μm) decreased from 85% to 5.1%; and the proportion of nanoplankton(3-20 μm) ranged during 9%-24% and showed no clear spatial change. There was a positive correlation of Synechococcus and pico-eucaryote abundances that increased towards the coastal waters from(2.58±0.21)×10~6 to(2.29±0.10)×10~8 cells·L~(-1) and from(1.62±0.91)×10~5 to(1.83±0.46)×10~7cells·L~(-1), respectively. In addition, our results indicated that the spatial variability of total surface phytoplankton biomass was mainly regulated by picoplankton abundance in the surveyed waters.