title: Distribution of picoplankton in the northeastern South China Sea with special reference to the effects of the Kuroshio intrusion and the associated mesoscale eddies.
abstract: We investigated picoplankton distribution patterns and environmental variables along an east-to-west transect in the northeastern South China Sea (SCS) during late winter 2016, giving us the opportunity to examine the impacts of the Kuroshio intrusion and the associated eddies. The results indicated that the subsurface (50-75m) phytoplankton biomass chlorophyll (Chl a) maximum (SCM) disappeared and was replaced by higher Chl a in the middle part of the transect due to the impacts of the Kuroshio intrusion and mesoscale eddies. Both flow cytometry and pyrosequencing data revealed that picoplankton abundance and community structure were significantly influenced by perturbations in complex physical processes. Picoeukaryotes represented most of the total phytoplankton biomass, and their maximum abundance (>104cellsmL-1) occurred within cyclonic eddy-affected regions (Stations 11 and 12), whereas the abundance of Prochlorococcus was the lowest in these regions. Prochlorococcus showed a higher abundance in the Kuroshio-affected area, while Synechococcus was mostly distributed at the upper well-lit depths, with its maximum abundance observed in surface waters (0-30m) adjacent to the cyclonic eddy center. Heterotrophic bacteria (HBA) displayed high abundance along the transect, consistent with the total phytoplankton biomass. Phylogenetic analysis revealed 26 bacterial phyla, with major components belonging to Proteobacteria, Cyanobacteria, Actinobacteria, and Bacteroidetes, as well as SAR406. Notably, relatively more Rhodobacterales, Flavobacteriales, Alteromonadales, and Vibrionales that were distributed in surface waters of the cyclonic eddy center were specifically associated with the phytoplankton (mainly picoeukaryotes) bloom. Our study highlights the impacts of the Kuroshio intrusion in regulating the microbial ecology of the northeastern SCS and the potential coupling between phytoplankton and bacteria.
authors.affiliation: Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China; University of Chinese Academy of Sciences, Beijing 100049, China; Guangdong Provincial Key Laboratory of Applied Marine Biology, West Xin(')gang Road 164#, Guangzhou 510301, China.
authors.forename: Jiajun
authors.initials: J
authors.lastname: Li
authors.affiliation: Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China; University of Chinese Academy of Sciences, Beijing 100049, China; Guangdong Provincial Key Laboratory of Applied Marine Biology, West Xin(')gang Road 164#, Guangzhou 510301, China.
authors.forename: Xin
authors.initials: X
authors.lastname: Jiang
authors.affiliation: Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China; Guangdong Provincial Key Laboratory of Applied Marine Biology, West Xin(')gang Road 164#, Guangzhou 510301, China.
authors.forename: Gang
authors.initials: G
authors.lastname: Li
authors.affiliation: State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China.
authors.forename: Zhiyou
authors.initials: Z
authors.lastname: Jing
authors.affiliation: Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China; Guangdong Provincial Key Laboratory of Applied Marine Biology, West Xin(')gang Road 164#, Guangzhou 510301, China.
authors.forename: Linbin
authors.initials: L
authors.lastname: Zhou
authors.affiliation: Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China; Guangdong Provincial Key Laboratory of Applied Marine Biology, West Xin(')gang Road 164#, Guangzhou 510301, China.
authors.forename: Zhixin
authors.initials: Z
authors.lastname: Ke
authors.affiliation: Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China; Guangdong Provincial Key Laboratory of Applied Marine Biology, West Xin(')gang Road 164#, Guangzhou 510301, China. Electronic address: tanyh@scsio.ac.cn.
authors.forename: Yehui
authors.initials: Y
authors.lastname: Tan
mesh_terms: D001419:Bacteria / Q000302:isolation & purification; D018533:Biomass; D002681:China; D010802:Phylogeny; D010839:Phytoplankton / Q000302:isolation & purification*; D048929:Prochlorococcus / Q000302:isolation & purification; D012623:Seawater; D046940:Synechococcus / Q000302:isolation & purification; D014872:Water Movements
keywords: Bacteria; Community structure; Kuroshio intrusion; Mesoscale eddy; Picoplankton; South China Sea