Physiological ecology of Noctiluca having phototrophic endosymbiont

2022 Fiscal Year Final Research Report

• Project/Area Number: 18K19239
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Review Section: Medium-sized Section 40:Forestry and forest products science, applied aquatic science, and related fields
• Research Institution: Soka University
• Principal Investigator: Furuya Ken 創価大学, プランクトン工学研究所, 特別教授 (30143548)
• Project Period (FY): 2018-06-29 – 2023-03-31
• Keywords: ヤコウチュウ / 赤潮 / 共生藻 / 温暖化

Outline of Final Research Achievements

The Green Noctiluca with symbiotic algae Pedinomonas noctilucae has its northern limit in the Luzon Strait and the Vietnam coast in the South China Sea, which approximately corresponds to the isotherm of 25℃ sea surface temperature in winter. Through cultivation experiments using four strains of Green Noctiluca and two isolated strains of symbiotic algae, it has been revealed that the northern limit of Green Noctiluca reflects the high-temperature dependence of symbiotic algae's growth and that the distribution of Green Noctiluca may shift northward with the increasing winter water temperature due to global warming. Both Green Noctiluca and symbiotic algae have a preference for reduced nitrogen such as ammonium, indicating the possibility of Green Noctiluca spreading and establishing in areas north of the northern part of the South China Sea that have high concentrations of reduced nitrogen due to cultural eutrophication.

Free Research Field

生物海洋学

Academic Significance and Societal Importance of the Research Achievements

南シナ海では温暖化により、冬季の海水温が上昇傾向にあり、ミドリヤコウチュウの分布の北限が今後北進する可能性が、本研究の結果明らかになった。即ち、今後地球温暖化により海水温が上昇した場合、南シナ海の北側に冬季に水温25°C以上の海域が出現し、ミドリヤコウチュウが越冬し得る海域が拡大する。北進先の中国沿岸域では人口増加や都市化による富栄養化が進んでおり沿岸水へのアンモニウムをはじめとした還元態窒素の供給が増えると考えられ、ミドリヤコウチュウの定着しやすい環境が存在すると考えられる。このため、高密度のミドリヤコウチュウブルーム発生による環境悪化や漁業被害の可能性が懸念される。