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[D-1.1 Study on the Mechanism of Variation in Ocean Element Cycle Accompanied with the Shifts of Dominant Species(Final Report)]

[Contact Person]

Shigeki Harada
Senior Researcher, Ocean Research Team
Global Environment Division
National Institute for Environmental Studies
16-2 Onogawa, Tsukuba, Ibaraki 305 Japan
Phone +81-298-50-2509, Fax +81-298-51-4732
E-mail sharada@nies.go.jp

[Total Budget for FY1993-1995]

52,360,000 Yen (FY1995 17,702,000 Yen)

[Abstract]

　A mesocosm(marine enclosure; 5m in diameter and 18m in depth) was developed in the Seto-Inland Sea, Japan. Vertical mixing in the upper layer(0-5m) was provided by a circulation system. This system created gentle upward flow and then suspended non-motile phytoplankton species such as diatoms. The dominant phytoplankton species were categorized into centric diatoms, pennate diatoms, dinoflagellates and others. Succession of these species was explained by the changing nutrient(N, P, Si) availability and grazing by zooplankton. Stable carbon isotope tracer experiments were done, using the bottle incubation technique. ¹³C-DIC or ¹³C-DOC was added into the bottles in order to know the transformation rates from DIC to>100μm POC(through photosynthetic loop) and those from DOC to>100μm POC(through bacterial loop). Our results suggested that higher role of bacterial loop than previously reported, especially when Doliollida dominated the zooplankton community.

[Key Words]

Mesocosm, Species Change, Element Cycle, Photosynthesis, Bacterial Loop