Spatial and temporal variation of picoplankton distribution in the Yellow Sea, China

Seven surveys were carried out in April, September, October, December 2006 and March, May, August 2007 in the Yellow Sea, China. Variations in the spatial and temporal distribution of Synechococcus, picoeukaryotes and heterotrophic bacteria are quantified using flow cytometry. Synechococcus and heterotrophic bacteria are most abundant from late spring to autumn, while picoeukaryotes concentration is high in spring. Synechococcus and heterotrophic bacteria concentrated high in the northwest part of the Yellow Sea in spring and autumn, while picoeukaryotes distributed evenly over the whole study area except for a small frontal zone in the coastal area on the west (in spring) and central Yellow Sea (in autumn). Under mixing conditions, the vertical distribution of the three picoplankton groups showed a well-mixed pattern. Upon a well-established stratification, the maximum abundance of picoplankton occurred above the mixed layer depth (similar to 30 m). Cell sizes of Synechococcus and picoeukaryotes were estimated by converting forward scatter signals (FSC) from cytometry analysis to cell diameter, showing the results of 0.65-0.82 mu m for Synechococcus and 0.85-1.08 mu m for picoeukaryotes. The average integrated carbon biomasses ranged 15.26-312.62 mgC/m(2) for Synechococcus, 18.54-61.57 mgC/m(2) for picoeukaryotes, and 402.63-818.46 mgC/m(2) for heterotrophic bacteria. The distribution of Synechococcus and heterotrophic bacteria was temperature dependent, and picoplankton presence was poor in the Yellow Sea Cold Water Mass.