Diffusion and persistency of the freshwater cyanotoxin in the marine ecosystem.

2019 Fiscal Year Final Research Report

• Project/Area Number: 17K00639
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Environmental risk control and evaluation
• Research Institution: Kumamoto Health Science University
• Principal Investigator: Takahashi Tohru 熊本保健科学大学, 保健科学部, 教授 (70369122)
• Co-Investigator(Kenkyū-buntansha): 正木 孝幸 熊本保健科学大学, 保健科学部, 教授 (00746232)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: ミクロシスチン / 分解菌 / 諌早湾調整池 / 生物濃縮 / HABs

Outline of Final Research Achievements

The blooming of toxic cyanobacteria has become an annual event constant in the Isahaya Bay reservoir from the summer to the autumn. Our 24hrs consecutive field survey estimated that about 52kg of strong hepatotoxin, microcystines (MCs) was produced and 40% of them deposited in the bottom in the blooming season. MCs spreads with drainage in the sea area. However, cyanobacteria of the fresh water origin are thought to perish and MCs are degraded in the sea area, and has not attracted attention. However, laboratory experiment revealed that the MCs are not degraded at less than 20C, and it was confirmed by real time PCR that the bacterial degrading did not function. This support the result of field survey that MCs content of the Ariake Sea’s sediment is higher in winter (non-blooming season of cyanobacteria) than that in summer (blooming season).

Free Research Field

海洋生態学

Academic Significance and Societal Importance of the Research Achievements

大規模な有毒シアノバクテリアの発生は世界各地で報告されているが、淡水域で産生された毒素の行方や分解過程については未解明な点が多い。今回、我々は、窒素消費からミクロシスチンの産生量を推定し、その分解は低温では進まないことを示した。そのため、海域生態系には未分解のミクロシスチンが残留・循環している事が示された。もちろん、この事は有明海特有の現象ではない。例えば、韓国ナクトンガンの河口域で厳冬期に採取された堆積物に高い濃度のMCsが残留している事が確認された。したがって、今後は、有毒アオコ発生時には下流のエコトーンから海域に至る調査が必要である事を示した。