Impact assessment of Noctiluca scintillans red tide on nutrient dynamics, biological processes in lower trophic levels and material cycle in the neritic area of Sagami Bay

2020 Fiscal Year Final Research Report

• Project/Area Number: 18K05794
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 40030:Aquatic bioproduction science-related
• Research Institution: Nihon University
• Principal Investigator: ARA Koichi 日本大学, 生物資源科学部, 教授 (40318382)
• Project Period (FY): 2018-04-01 – 2021-03-31
• Keywords: 夜光虫赤潮 / 細胞内栄養塩含有量・濃度 / 栄養塩プール / 排泄速度 / 栄養塩滲出（溶出）速度 / 栄養塩供給 / 窒素・リン収支 / 相模湾沿岸域

Outline of Final Research Achievements

Field investigations were carried out in the neritic area of Sagami Bay to test hypotheses whether: (1) red tides of Noctiluca scintillans exacerbate eutrophication (i.e., rise in nutrient concentrations, phytoplankton standing crop and/or primary productivity); and (2) Noctiluca-related eutrophication can change phytoplankton assemblages, with the highly skewed toward diatom dominance shifting towards non-diatom blooms. These two variations were observed frequently and temporally in the upper layer during high Noctiluca abundances in spring-autumn, although no Noctiluca red tide occurred. Moreover, N and P supply by Noctiluca excretion and dissolution contributed high percentages to nutrient concentrations and requirement of phytoplankton primary productivity in the euphotic zone during the periods of high Noctiluca abundances and low nutrient concentrations in spring-summer, while N. scintillans was greater contributor to nutrient supply than micro- and mesozooplankton communities

Free Research Field

水圏生産科学関連

Academic Significance and Societal Importance of the Research Achievements

本研究によって得られた研究成果は、現場海域での水質環境（栄養塩動態）ならびに海洋生態系（低次生物過程、一次生産速度、物質収支）に及ぼす夜光虫の影響を定量的に評価する際に必要な知見とパラメーターをほぼ全て兼ね備えている。よって、本研究成果は、当該海域のみならず、夜光虫赤潮が頻繁に発生する本邦ならびに世界の多くの内湾・沿岸域に応用できると共に、人為的な環境変化に対する沿岸生態系の応答予測にも繋がるものとなった。