Drastic changes carbon flow in marine organisms under anoxic water masses in hyperclosed seas.

2023 Fiscal Year Final Research Report

• Project/Area Number: 21K19151
• 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: Kumamoto University
• Principal Investigator: Shimanaga Motohiro 熊本大学, くまもと水循環・減災研究教育センター, 教授 (70345057)
• Co-Investigator(Kenkyū-buntansha): 和田 実 長崎大学, 水産・環境科学総合研究科(水産), 教授 (70292860) ; 山田 雄一郎 北里大学, 海洋生命科学部, 講師 (80458744) ; 森 郁晃 国立研究開発法人海洋研究開発機構, 超先鋭研究開発部門(高知コア研究所), 特別研究員(PD) (60849537)
• Project Period (FY): 2021-07-09 – 2024-03-31
• Keywords: 貧酸素 / ダークカーボン / 食物連鎖 / 生物群集構造

Outline of Final Research Achievements

In the Omura Bay, the most enclosed sea among the three investigated inland seas, bacterivorous nematodes and copepods increased in the meiofaunal community in bottom sediment under seasonal hypoxia in each summer, where sulfate-reducing bacteria performing anoxic respiration, played important roles in carbon flow in sediment. Our study also showed that bacteria that perform dark carbon fixation are present in all seasons, which would lead to drastic rotation from “blue” to “dark” carbon flow as soon as seafloor conditions change in the area.
On the other hand, in the sea floor in the other more opened areas, e.g. Yatsushiro Sea, Dissolved oxygen concentrations in bottom water were rarely below the criteria of hypoxia, suggesting that the effects of “carbon flow change” would be limited in those areas at present.

Free Research Field

海洋生態学

Academic Significance and Societal Importance of the Research Achievements

閉鎖性の最も高い大村湾では、夏季貧酸素発生時に小型底生生物群集中の化学合成細菌を主たる餌とする種具の割合が劇的に変化するが、ダークカーボン固定を行う細菌は季節を問わず海底堆積物深層に常に存在するためカーボンフローの劇的な変化が起きることを示唆した点が、本研究の学術的意義である。今世紀末までに温暖化の影響により海全体の酸素濃度低下懸念されるが、この低下が沿岸域の水産業などに与える影響を考えると、大村湾に次いで閉鎖性が高いが夏季貧酸素化が深刻とは言えない八代海海底生態系に今後十年単位で生じる変化に注目する必要があるだろう。