Fig. 3 Boxplots displayed the spatiotemporal distributions of richness (a. Chao 1) and diversity (b. Shannon) of microbial flagellate communities. The hollow diamonds represented average values of individual index in each group. The numbers in parentheses represent the sample size for each water masses, including two size fractions. Water masses with less than 5 samples were not included in this analysis. The Mc and Zd were considered as coastal waters, the Cm, Es, and Ss were considered as mixed waters, while the Ks, Km, Sm, Ss-2017, Su-2017, and Pu-2017 were assorted to oceanic waters. Asterisk indicates significant differences at the level of p < 0.01 (**, p < 0.01; ***, p < 0.001).