A Preliminary Study Of Ultraphytoplankton In The Southern Yellow Sea In Summer And Winter

In this thesis, the distribution characteristics of ultraphytoplankton in the Southern Yellow Sea in summer and winter were studied using flow cytometry, and the relationship between ultraphytoplankton biomass and chlorophyll a concentration was analyzed. The main results are listed as following:Synechococcus and picoeukaryotes were the main dominant ultraphytoplanktonic groups in the Southern Yellow Sea, while Prochlorococcus was not detected in this study. The average cell density of Synechococcus was 6.2×104 cells/ml in summer, while its density was lower in winter (1.1×104 cells/ml). The mean cell numbers of picoeukaryotes in summer and winter were 9.8×103cells/ml and 6.2×103cells/ml respectively. Compared with Synechococcus (10.8μgC l-1), picoeukaryotes had a higher biomass (14.7μgC l-1). Furthermore, the biomass of Synechococcus decreased obviously to 1.9μgC l-1 when it turned to winter, while that of picoeukaryotes decreased slightly, still with a mean value of 9.2μgC l-1 in winter.The horizontal and vertical distribution features of Synechococcus were also investigated.As for the horizontal distribution, its density showed as a spot massive distribution in upper (lower than10 m) and bottom layer with the low value area locating at Northern Jiangsu inshore water and central northen sea area, while the 30 m layer assumed an increasing trend from seashore to the open sea in summer. In winter, the central sea area was the higher area compared with the northern and southern area. As for the depth profiles distribute, in summer, the stations in southern area had no an obvious maximum layer and the density of all layers were lower; the densities of the stations in central area have no significant vertical differences; in northern area, the maximum density appeared in the thermal layer , while the cell abundance decreased along with the increasing water depth under the thermal layer; the vertical distribution was more complex in the open sea area. In winter, there were no apparent differences among different water layers. Besides, the horizontal distribution features of picoeukaryotes cell density were also studied: In summer, the horizontal distribution of picoeukaryotes in surface,10 m and bottomlayer were similar with a decreasing tendency from seashore to the open sea, but the separatrix between higher and lower value was nearer to the seashore; the density in the 30 m layer of northern area was higher compared with the southern part. In winter, the high value area located at the central part of the Southern Yellow Sea. As for the vertical distribution, in summer, the stations in southern area had no obvious differences and the densities of all stations besides nearshore station were low; in central area, the cell abundance in the euphotic layer was larger than other layers; in northern area, the maximum density appeared in the thermal layer; in the open sea area, the vertical distribution had no obvious differences. In winter, there were no obvious differences among various water layers.Picophytoplankton (< 2μm) contributed about half of the total chlorophyll a concentration in summer, while this percent decreased to less than 1/3 in winter. The total chlorophyll a was positively correlated to the pico- chlorophyll a and negatively to the pico-/total ratio. Therefore, phytoplankton with larger size dominated when chlorophyll a concentration was high, while phytoplankton with smaller size dominated when chlorophyll a concentration was low.The distribution features Synechococcus was similar with pico-/total chlorophyll a ratio, so they had positively correlative relationship. Chlorophyll a concentration was tightly correlated to the picophytoplankton, but the relationships between Chlorophyll a and Synechococcus were more complex. Correlations between Synechococcus and picophytoplankton were different in summer and in winter. They were negatively related in summer, but significantly positively correlated in winter.