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The dynamics of microbial and herbivorous food webs in a coastal sea with special reference to intermittent nutrient supply from bottom intrusion |
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| Authors: | Shin-ichi Nakano Yuji Tomaru Toshiya Katano Atsushi Kaneda Wataru Makino Yuichiro Nishibe Miho Hirose Masashi Onji Shin-Ichi Kitamura Hidetaka Takeoka |
| Institution: | 1. Center for Marine Environmental Studies, Ehime University, Bunkyo-cho 3, Matsuyama, 790-8577, Ehime, Japan 2. Laboratory of Aquatic Food Web Dynamics, Faculty of Agriculture, Ehime University, Tarumi 3-5-7, Matsuyama, 790-8566, Ehime, Japan ((e-mail 3. Faculty of Agriculture, Ehime University, Tarumi 3-5-7, Matsuyama, 790-8566, Ehime, Japan 4. Current address: National Research Institute of Fisheries and Environment of Inland Sea, Fisheries Research Agency, Maruishi, 2-17-5, Ohno-cho, Saeki-gun, 739-0452, Hiroshima, Japan 5. Current address: Graduate School of Life Science, Tohoku University, Aramaki Aza Aoba, Sendai, Miyagi, 980-8578, Japan 6. Current address: Graduate School of Fisheries Science, Hokkaido University, 3-1-1 Minatocho, Hakodate, 041-8611, Hokkaido, Japan 7. Current address: Nippon Becton Dickinson Company, Ltd., Akasaka DS Building, 5-26, Akasaka 8-Chome, Minatoku, Tokyo, 107, Japan 8. Current address: Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka, 812-8581, Fukuoka, Japan 9. Current address: Department of Aqualife Medicine, Yosu National University, San 96-1, Dunduk-dong Yeosu, Jeollanam-do, 550-749, Korea |
| Abstract: | Seasonal changes in abundance of planktonic microorganisms, together with some physico-chemical variables, were monitored monthly from May 1999 to March 2002 in the surface water of a coastal bay where nutrients are mainly supplied by intermittent intrusions of deeper water (bottom intrusion). No significant bottom intrusion was detected in 1999 but large or frequent bottom intrusions were found from June to October in 2000, and again from mid-June only to late July in 2001. These results indicate that there is a different nutrient supply every year, and peaks in the abundance of dominant eukaryotic phytoplankton (diatoms and dinoflagellates) roughly corresponded to the occurrences of bottom intrusions. By contrast, there was a cyclic seasonal pattern of autotrophic picoplankton (APP) cell density, which reached maxima in August of every year at very similar levels (4.0-5.0 × 105 cells ml–1). Thus, the seasonal abundance of APP was apparently independent of the occurrence of bottom intrusions. Seasonal changes in cell densities of heterotrophic bacteria showed similar trends to the APP, and temperature-dependent growth of both was indicated. The present study suggests that the matter cycling in the bay varies as a result of shifts in the dominant food linkages, from a microbial food web to a herbivorous food web, due to intermittent nutrient supplies from bottom intrusions. |
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