Elucidation of rapid environmental changes and ecosystem dynamics in the Tsugaru Strait
～Ecosystem response to the Pacific Decadal Oscillation～

1. Key Points

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During the ecosystem monitoring period from 2010 to 2018, seawater temperature in the Tsugaru Strait increased during spring at a rate 3–20 times faster than the anticipated rate of future global warming, whereas it decreased more rapidly during summer and fall than the increasing trend.

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The rate of increase in carbon dioxide concentration was 1.5–2 times higher in seawater than in the atmosphere, resulting in accelerated progression of ocean acidification.

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Diatoms, which are large phytoplankton, were believed to be at a disadvantage in competing for dominance within communities comprising smaller phytoplankton under the effects of ocean acidification. During the survey period, however, the cell density of diatoms showed an increasing trend. This increase in diatom abundance resulted in improved productivity of plankton-feeding aquaculture species, such as scallops.

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This study comprehensively elucidated that the complex ecosystem of the Tsugaru Strait, including the physical and chemical components of seawater, as well as the plankton and aquaculture species, was influenced by large-scale natural variability.

2. Overview

Researcher, Koji Sugie, from the Earth Surface System Research Center; Researcher, Masahide Wakita, from Mutsu Institute for Oceanography; and colleagues from the Research Institute for Global Change at the Japan Agency for Marine-Earth Science and Technology are involved a joint monitoring research in collaboration with Tohoku Environmental Science Services Corporation, Aomori Prefectural Industrial Technology Research Center, Faculty of Fisheries Sciences at Hokkaido University, and Japan Fisheries Research and Education Agency, which has been ongoing since 2010. The results of this research revealed that the dynamics of seawater components and phytoplankton in the eastern Tsugaru Strait (Figure 1) were influenced by the Pacific Decadal Oscillation (*1) and that the changes in the ecosystem affected the productivity of aquaculture species. The results of this research, which comprehensively assesses the impact of large-scale temporal and spatial natural variability, such as the Pacific Decadal Oscillation, on the entire regional ecosystem, are of paramount importance in enhancing our understanding of the complex Earth system.

Figure 1. Examples of frequently observed protists in the present study. Scale bars in each figure represent 100 ㎛.

The findings of this study will be published in “Environmental Research” on May 19 (Japan time). This study received financial support from JSPS Grants-in-Aid for Scientific Research (JP15H02835, JP20H04349, JP20K04072).