| Summary: | 碩士 === 國立東華大學 === 海洋生物多樣性及演化研究所 === 98 === Upwelling is a common phenomenon in coastal waters. In this study, we investigated the variations of nutrients and different size fractions of phytoplankton in Nanwan Bay before and after upwelling during a short time period. The study was conducted on July 2, August 18, and September 3, 2009. Data from July and August showed a drop in temperature and rise in salinity, indicated a significant upwelling during the sampling period, while no change in temperature and salinity was observed in September. Nitrate and silicate concentrations were significantly higher in the surface and 15 m depth in July after the upwelling, however no significant change in both nutrients in August, suggesting that upwelling might not necessarily couple with high nutrient concentration. Size-fractionated Chl a concentrations, phytoplankton densities, as well as Prochlorococcus increased significantly in the surface and 15 m depth in both July and August. No significant change in nutrient and Chl a concentrations, phytoplankton nor picoplankton density in September, when no upwelling was observed. Diatom genus Chaetoceros was the dominant taxon during all sampling periods, while dinoflagellates were observed only before and during the upwelling. The study concluded that upwelling may or may not occur in Nanwan Bay, and when it does, it may not necessarily couple with high nutrient concentration. However the high picoplankton and nanophytoplankton densities brought by upwelling may be an important food source for filter-feeders in the coral reef ecosystem.
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