AME 46:191-201 (2007)  -  doi:10.3354/ame046191

Distribution of prokaryotic picophytoplankton from Seto Inland Sea to the Kuroshio region, with special reference to ‘Kyucho’ events

Toshiya Katano1,2,*, Atsushi Kaneda1, Naoto Kanzaki3, Yumiko Obayashi1, Akihiko Morimoto4, Goh Onitsuka5, Hideichi Yasuda5, Sotaro Mizutani6, Yoshihide Kon6, Kazuhiro Hata6, Hidetaka Takeoka1, Shin-ichi Nakano3

1Center for Marine Environmental Studies, Ehime University, Bunkyo-cho 3, Matsuyama 790-8577, Japan
2Department of Life Science, Hanyang University, Seoul 133-791, Korea
3Faculty of Agriculture, Ehime University, Tarumi 3-5-7, Matsuyama 790-8566, Japan
4Hydrospheric Atmospheric Research Center, Nagoya University, Nagoya 464-8601, Japan
5Department of Fisheries Information and Management, and 6TV ‘Tenyo-maru’, National Fisheries University, Shimonoseki 759-6595, Japan

ABSTRACT: A ‘Kyucho’ (an intrusion of warm surface water) occurs in the Bungo Channel, located in southwestern Japan. The abundances of Prochlorococcus and Synechococcus during a Kyucho, together with physical and chemical environmental factors, were investigated from the Kuroshio region to the Seto Inland Sea, via Bungo Channel, from 26 November to 5 December 2003. With the occurrence of the Kyucho, oceanic water intruded from the Kuroshio region into the middle of the Bungo Channel. The abundance of Prochlorococcus was the highest in the Kuroshio region and the southern part of the Bungo Channel (>25 × 103 cells ml–1), low in the northern part of the Bungo Channel (<1 × 103 cells ml–1), and below detection levels in the Seto Inland Sea. A relatively high abundance of Synechococcus cells (>15 × 103 cells ml–1) was detected in the Kuroshio region and in the southern part of the Bungo Channel, but the abundance (<6 × 103 cells ml–1) was low in other regions. In the Kuroshio region and the southern part of the Bungo Channel, high-phycourobilin (PUB)-type cells were dominant (>90%); at this location, most of the available light in the deeper layer (>25 m depth) was in the 450 to 500 nm range, corresponding to the peak absorbance of PUB. In contrast, the abundance of low-PUB-type cells accounted for >75% of the total in the northern part of the Bungo Channel and in the Seto Inland Sea, where most of the available light in the deeper layer (>10 m depth) was in the 480 to 560 nm range, including the peak absorbance of both PUB and phycoerythrobilin (PEB). These results indicate that Synechococcus cells of high-PUB type, which have a higher Ex 495:545 (>1.5; ratio of orange fluorescence intensity excited at 495 nm to that at 545 nm), as well as Prochlorococcus cells were advected to the Bungo Channel by the Kyucho. The co-occurrence of the 2 pigment types of Synechococcus in coastal waters is highly affected by a physical process, such as the Kyucho.


KEY WORDS: Prochlorococcus · Synechococcus · Kyucho · Kuroshio · Phycoerythrin · Pigment type · Advection · Dual laser flow cytometry · Spectrofluorometry


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