IN SITU DAILY GROWTH RATE OF PROCHLOROCOCCUS AT THE CHLOROPHYLL MAXIMUM LAYER IN THE SOUTHERN SOUTH CHINA SEA:AN ESTIMATION FROM CELL CYCLE ANALYSIS

Prochlorococcus is the dominant population of the autotrophs in the oceanic area in theSouth China Sea; and contributes significantly to picoplanktonic (【2μm) carbon biomass. However, thereis no availabe data on its growth the and productivity so far. In the present study, the in situ populationgrowth rate of Prochlorococus at the chlorophyll maximum layer at 6 .3°N, 110°E in the South China

Prochlorococcus is the dominant population of the autotrophs in the oceanic area in the South China Sea; and contributes significantly to picoplanktonic ( < 2 μm) carbon bioraass. However, there is no available data on its growth rate and productivity so far. In the present study, the in situ population growth rate of Prochlorococcus at the chlorophyll maximum layer at 6.3°N, 110°E in the South China Sea was estimated through the cell cycle approach. The daily growth rate of Prochlorococcus calculated from the percentage of cells undergoing S and G2 phases to the total population number during one diel cycle at the sampling station was 0.54 /d, i.e., 0.72 division/d. Results were comparable to those reported in other oceanic areas. Based on that growth rate, and taking the conversion of carbon biomass per cell as 53 fg C/ cell for Prochlorococcus , the depth integrated productivity of Prochlorococcus was 195 mgC/(m2 ·d) .