Changes in the abundance and composition of picophytoplankton in relation to the occurrence of a Kyucho and a bottom intrusion in the Bungo Channel,Japan |
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| Authors: | Miho Hirose Toshiya Katano Yuichi Hayami Atsushi Kaneda Takeshi Kohama Hidetaka Takeoka Shin-ichi Nakano |
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| Institution: | 1. Faculty of Agriculture, Ehime University, Tarumi 3-5-7, Matsuyama 790-8566, Japan;2. Center for Marine Environmental Studies, Ehime University, Bunkyo-cho 3, Matsuyama 790-8577, Japan;3. Department of Life Science, Hanyang University, Seoul 133-791, South Korea;4. Faculty of Engineering, Ehime University, Bunkyo-cho 3, Matsuyama 790-8577, Japan;5. Ariake Sea Research Project, Saga University, Honjo-cho 1, Saga 840-8502, Japan |
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| Abstract: | The Bungo Channel in southwestern Japan receives both warm, called Kyucho, and cold deep-water intrusions (bottom intrusion) from the Pacific Ocean. Abundances of Prochlorococcus, Synechococcus, and eukaryotic picophytoplankton were monitored from 18 July to 17 August 2001 to clarify whether advected picophytoplankton from the Pacific Ocean can grow in the channel or not. Synechococcus cells were further discriminated into low- and high-PUB types according to their fluorescence property in flow cytometry. From 18 to 25 July, the water temperature decreased by 3 °C at a 5-m depth at all stations, indicating the occurrence of a bottom intrusion. From 25 July to 4 August, a Kyucho occurred and the water temperature rapidly increased. From 4 to 17 August, a bottom intrusion and a Kyucho both occurred twice, although the intensities were smaller than those occurring until 4 August. From 18 to 30 July, the abundance of both Prochlorococcus and a high-PUB type of Synechococcus drastically decreased because of a bottom intrusion; however, the abundances rapidly increased due to the advection by a Kyucho. These advected cells increased from 4 to 17 August in the channel and Kitanada Bay. Changes in the abundance of low-PUB type of Synechococcus and eukaryotic picophytoplankton were less noticeable than those in the abundance of Prochlorococcus and high-PUB type. The present study demonstrated that oceanic picophytoplankton advected by the Kyucho could grow in the channel. However, abundances of low-PUB type and eukaryotic picophytoplankton increased higher than those of Prochlorococcus and high-PUB type did. Thus, these oceanic phytoplankters will be excluded when Kyucho does not occur for a long time. The co-occurrence of various types of picophytoplankton found in the channel is probably achieved by both Kyucho event and their growth capability in the channel. |
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| Keywords: | Kyucho bottom intrusion picophytoplankton flow cytometry phycourobilin (PUB) |
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