| Summary: | 碩士 === 國立臺灣海洋大學 === 水產養殖學系 === 95 === Abstract
This research investigated seasonal variation of diatom sedimentation in the basin of the South China Sea and it’s relationship with the diatom biomass in the euphotic zone. Factors affected diatom biomass variation in the euphotic zone were also studied. Sedimentation samples were obtained from the sediment traps deployed by the National Center for Ocean Research. Totally there were 36 samples. Collecting period covered four seasons, from August 8, 2004 to May 25, 2006, including three deployments which were from August 8, 2004 to February 16, 2005, April 1, 2005 to October 10, 2005, and November 15 2005 to May 25, 2006, respectively. There were five samples collected from euphotic zone during August 3, 2004 and December 30, 2005. Results indicated that nitrate availability is the most important factor affecting diatom biomass dynamics in the euphotic zone. High concentration of diatom was observed in winter and spring when surface nitrate was relatively high. In contrast, during summer and autumn when surface nitrate concentration was low, the diatom biomass was also relatively low. Irradiance intensity seemed not an important factor for seasonal variation of diatom abundance. Seasonal variation of diatom abundance in the sediment trap also showed higher in spring and winter than that in summer or autumn. However, the dynamic of the diatom abundance between the sediment traps and the euphotic zone was not significantly correlated. Nitrate concentration also affected the dominance of diatom assemblages. During winter when nitrate was high, centric diatoms outcompeted pennate diatoms. On the contrary, pennate diatoms outcompeted centric diatoms during summer and autumn when surface nitrate concentration was low. Spring was a transitional period. During then centric diatoms decreased in abundance gradually and the assemblages were shifted to be dominated by pennate diatoms.
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