Variations of picoplankton abundances during blooms in the East China Sea

• Bloom events were observed in the East China Sea during both spring and summer.
• Different distribution patterns for picoplankton during blooms.
• Ciliate and salinity tended to be the control factor in spring.
• Temperature and chlorophyll a concentration were important variables in summer.

The picoplankton distribution in the East China Sea was investigated during bloom events occurred in spring (June) and summer (August) 2011. In spring, there was no significant difference in picoplankton abundances between areas where bloom conditions were or were not established. In the bloom area, Synechococcus, picoeukaryotes and heterotrophic prokaryotes exhibited at only some stations that abundances were higher than those within the non-bloom area. In summer, the abundances of Synechococcus and picoeukaryotes were significantly higher inside the bloom area than outside. Among the picoplankton components, heterotrophic prokaryotes represented the highest carbon biomass.Factors that most influenced picoplankton distribution under bloom conditions in the East China Sea varied with season. In spring, ciliates and salinity tended to be the main factors, whereas in summer, this role was played by temperature and chlorophyll a concentration.