| Summary: | 碩士 === 國立中山大學 === 海洋生物科技暨資源學系研究所 === 100 === This research studied the seasonal and spatial dynamics for abundance of picophytoplanktons (including Prochlorococcus spp., Synechococcus spp. and picoeukaryotes) in the South China Sea (SCS) and the Kuroshio. Waters were collected during five cruises between August 2009 and December 2010. Growth rates were determined in two size fractioned waters, <2 um and <10 um, after incubation. The differences of growth rates between the two size fractions were defined as the grazing
rates. Before the incubation, waters were enriched with FeCl3, EDTA, or NH4Cl to examine the possible shortage of Fe or nitrogen. Abundances of picophytoplanktons and
nanoflagellates were examined using a flow-cytometry and a microscope, respectively.
Prochlorococcus was more abundant in the warm than the cold seasons and in the Kuroshio and the basin of the SCS than in the shelf and slope of the SCS. In the high abundance seasons/regions, low irradiance enhanced the growth rates of Prochlorococcus. Although both of the growth rates and grazing rates were high during then, the growth rates were found higher than the grazing rates. Addition of EDTA enhanced the growth rates that was likely attributed to its chelating with toxic trace metals (such as Cd2+, Cd2+) and/or with growth necessity trace metals (such as Co2+).
The seasonal/spatial distributions for Synechococcus were in contrast to that of Prochlorococcus. High growth rates of Synechococcus were related to high nitrate concentrations and the low irradiance. The growth rates were higher than the grazing rates in the high nitrogen seasons/regions when/where irradiance was also relatively low. EDTA also enhanced the growth of Synechococcus, and was likely due to its chelating to remove Cd2+ and/or to retain Co2+.
Distributions of picoeukaryotes were similar to that of Synechococcus. Factors affected its dynamics were not clear because of its complicated compositions.
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