2020년 하계 장강저염수가 식물플랑크톤 다양성 및 개체수 변화에 미치는 역학: 이어도 해양과학기지 주변수역의 공간적 변화

Abstract

The expansion of the Changjiang Diluted Water (CDW) plume during summer is known to be a major factor influencing the phytoplankton diversity and community structure as well as regional marine environment of the northern East China Sea (ECS). The discharge of CDW plume was very high in the summer of 2020, and the cruise survey and stationary monitoring were carried out to understand the dynamics of changes in environmental characteristics and the impact on phytoplankton diversity and community structure. The study conducted the cruise survey from August 16 to 17 of 2020 using R/V Eardo, and carried out stay survey at the Ieodo Ocean Research Station (IORS) from August 15 to 21 of 2020 for analyzing phytoplankton diversity and community structure. The southwestern part of the survey area showed low salinity and high chlorophyll a fluorescence under the influence of CDW plume, whereas the southeastern part of the survey area indicated high salinity and low chlorophyll a fluorescence under the influence of the Tsushima Warm Current (TWC). The total chlorophyll a concentrations of surface water samples from 12 sampling stations showed that the nano-phytoplankton (20~3 μm) and micro-phytoplankton (>20 μm) were the dominant group during the survey period. Only stations strongly influenced by the TWC, presented about 50% of biomass contributed by pico-phytoplankton (<3 μm). Size distribution of phytoplankton in the surface water samples are related to nutrient supplies and areas where high nutrient (nitrate) supplies was provided by the CDW plume, showed higher biomass contribution by micro-phytoplakton groups. 45 genera of nano-phytoplankton and micro-phytoplankton groups were classified by using of morphological analyses. Among them, the dominant taxa were the diatoms and the dinoflagellates. The sampling stations affected by the TWC and low in nitrate concentrations showed high concentrations of photosynthetic pico-eukaryotes (PPE) and photosynthetic pico-prokaryotes (PPP). Most sampling stations presented phosphate-limited condition. Higher Synechococcus concentrations were enumerated for the sampling stations influenced by low-nutrient water of the TWC by using flow cytometry. As a result of NGS analysis, there were 29 clades of Synechococcus among PPP, and 11 clades showed a dominance rate of 1% or more at least once in one sample. Clade II was the dominant group in the surface water whereas various clades (Clades I, IV, etc) showed next dominant groups in the SCM layers. Prochlorococcus group, belongs to PPP, observed in the warm water region presented high-light adapted ecotype and did not appear in the northern part of the survey region. PPE analysis resulted 163 Operational Taxonomic Units (OTUs) indicating very high diversity. Among them, 11 major taxa showed dominant OTUs with more 5% at least one sample Amphidinium testudo was the dominant taxon in the surface water at the low-salinity region affected by the CDW plume, and the chlorophyta was dominant in the SCM layer. In warm water region affected by the TWC, various groups of the haptophytes were dominant. Observations from the IORS also presented similar results from the cruise survey results in biomass, size distribution and diversity of phytoplankton. The results of this study found various dynamic responses of phytoplankton influenced by the CDW plume. And, by comparing results from IORS and research cruise studies, the study confirmed that the IORS is an important observational station to conduct monitoring of dynamic impact of the CDW plume. It is necessary to establish an effective use of IORS in preparation for changes in the ECS summer environment and ecosystem due to climate change in the future research.