Fig.1 Maps and hydrographical properties of studied areas in the epipelagic waters of China marginal seas in spring. Maps of sampling sites (a); hydrographical properties of temperature and salinity (b) of different water masses that were identified based on the Supplementary Methods and were displayed in different colors in the left map (a); environmental variations of samples from different water masses displayed by principal component analysis (PCA) (c). The abbreviations of the water masses are: Mc , Minzhe coastal water; Cm , Coastal mixed water; Es , East China Sea surface water;Ks , Kuroshio surface water; Ss , South China Sea surface water. According to the salinity and the distance from the shore of the water masses, the Mc were considered as coastal waters, the Cm, Es, and Ss were considered as mixed waters, while the Ks were assorted to oceanic waters. The abbreviations of the environmental variables are: Temp, temperature; Sal, salinity; Fluo, fluorescence; SiO3-Si, Silicate; PO4-P, dissolved inorganic phosphorus; NO2-N, nitrite; Chl a , chlorophyll a ; Cyan, cyanobacteria; pico-Euk, pico-sized eukaryotic algae; PNF, pigmented nanoflagellate.