| This paper is the working results of flow cytometric measurements of ultraphytoplankton in East China Sea and Yellow Sea, which including the works of two cruises in autumn 2000 and spring 2001 and two-week time series observation in summer 2001. In addition, in situ enrichment experiments were designed at E2 station of spring cruise.In chapter one the types and characteristic of ultraphytoplankton are introduced first, then the working principle and protocols of flow cytometry for ultraphytoplankton measurements are also presented. The main purpose of this part is to make good understanding of the works in East China Sea and Yellow Sea.Chapter two is the research results and discussion, which consist of distributions of cell density, fluorescent characteristic per cell of ultraphytoplankton.Synechococcus and picoeukaryotes are abundant in all stations of East China Sea and Yellow Sea, and Prochlorococcus can't be found in near-shore stations. The community structure of ultraphytoplankton is very different in autumn and spring concluded by data comparison of two cruises. The cell density of Synechococcus in autumn is significantly higher than that in spring. During autumn cruise a high value Synechococcus density was observed by flow cytometry in upper layer of E2 and E6, which was 25. 73×104 cells/ml and 15. 92×104 cells/ml respectively. Whereas the higher value in spring cruise was found in surface layer of E6 and P2, which was 2.46 ×104和3 2. 01×104cells/ml respectively. Cell density of picoeukaryotes also changed much between two seasons. In autumn a high value in Yellow Sea was observed in El station, 0. 31×104cells/ml, and increased from E4 to outer station in East China Sea, the highest value was found in P2, 0. 46×104cells/ml. In spring a higher value were found in El, 1. 30×104cells/ml. 10 times increased as that in the same siteof last autumn. This condition is also true for E2 but inversely for E6, P2 and P1 station which declined about 10 times compared with data of last autumn. Prochlorococcuswas found in P3, E7, E6, P2 during autumn cruise, and in P2, P1 during spring cruise. The changes of Prochlorococcus distribution zones between two seasons perhaps are correlation with the influence of diluting fresh waters of Yangtze River.Observed from the depth profiles of ultraphytoplankton abundance, a parallel character can be found among Synechococcus, picoeukaryotes and nanoeukaryotes. The shape of profile are usually homogeneous in near-shore station during autumn cruise such as El, E3. In outer stations ultraphytoplankton dominated homogeneously in the upper mixlayer and decreased rapidly when depth was below the Thermocline. The condition of profiles in outer station didn't change much in spring cruise, but showed more variable in near-shore stations when observed in different time.Fluorescent characteristic per cell can be obtained by flowcytometric analysis. Based on fluorescence data of Synechococcus of all stations, two distinctly pigment-containing cell types coexisting can be found in some stations of East China Sea, which located in all depth of P3, mixlayer of E7, 40-meter depth of E6 of autumn cruise and in mixlayer of P2 of spring cruise. Perhaps they belongs two different stains. The zones of coexisting distribution can be influenced by hydrological conditions.In this paper, a method is used to estimate the biomass contribution of per population to total biomass that combined flow cytometric analyzing data and size-fractionated chlorophyll a data. The results of autumn cruise shows that Synechococcus is a important contributor to pico-chlorophyll a, especially in E2, E6, E7 also be true to total chlorophyll a, which the percent value is 69%, 56%, 56% respectively. But much more would be discussed and modified of this method if to be applied to biomass estimation on population level.The two-week time series observation demonstrated that the abundance of Synechococcus,picoeukaryotes and nanoeukaryotes in surface, 5-meter depth and bottom layer. For Synech...
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