| Summary: | 碩士 === 國立臺灣海洋大學 === 海洋環境化學與生態研究所 === 100 === Previous studies have indicated Synechococcus spp. are the major picophytoplankton in the East China Sea (ECS). Their population composition and phylogenetic distribution, however, are not investigated so far. The lack of this information will make it difficult to infer the relationship between Synechococcus ecology and global environmental changes. In this study, assemblages of Synechococcus spp. over the ECS in the summers 2009 and 2010 were revealed by a two-lasers flowcytometry, as well as by the phylogenetic analysis of phycocyanin operon, cpcBA-ITS. In the summer 2009, the phycoerytherin-rich (PE-rich) Synechococcus dominated in the water with a salinity of 31. In contract to the PE-rich Synechococcus, the phycocyanin-rich (PC-rich) Synechococcus preferred to grow in the low-saline coastal waters (salinity<31) near the mouth of the Chiangjian River. In addition, according to the result of cpcBA-ITS phylogenetic analysis, Synechococcus populations in the ECS were further categorized into at least 4 groups which contained a total of 14 operational taxonomic units. Among these, 3 groups, named ECS-1 to 3, belonged to PC-rich Syenchococcus: ECS-1 should be the species adapted in freshwater environment; ECS-2 and ECS-3 were characterized as novel marine PC-rich Syenchococcus. In the summer 2010, huge low-saline discharge occupied over half of the ECS due to the flooding arose in the Changjiang River. Except the decline of cell abundances, the distribution patterns of PE- and PC-rich Synechococcus were similar as that occurred in 2009. Plentiful terrestrial materials brought with the input of the Changjing River should be a critical factor to inhibit Synehcococcus growth in the summer 2010.
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