Abstract: To compare the responses of major planktonic groups in microbial food web, the red tide causative species Skeletonema costatum, Akashiwo sanguinea and solitary cells of Phaeocystis globosa, were introduced and incubated in the natural seawater, respectively. The results showed that both S. costatum and A. sanguinea underwent a lysis phase after proliferation during experiments. S. costatum declined after phosphate depletion and the phosphate was released back to water during lysis phase. Unlike S. costatum, phosphate concentration in A. sanguinea group reduced in both proliferation and lysis phase. P. globosa did not decline but sustained in stationary phase after nutrients depleted. The abundance of heterotrophic bacteria was significantly higher in S. costatum group than in other two groups (P<0.05). And compared with other algae, the highest abundance of ciliates, heterotrophic nanoflagellate (HNF) and pigmented nanoflagellate (PNF) appeared in A. sanguinea group (P<0.05). However, no significant differences in trophic structures of nanoflagellate (HNF/PNF) were found between A. sanguinea and S. costatum groups (P>0.05). Comparatively, the trophic structure of nanoflagellates in P. globosa group preferred heterotrophy (P<0.05) as a result of significantly decreased PNF (P<0.05), and the abundance of ciliates was also the lowest at the end of experiments (P<0.05). The results suggest that the effects of P. globosa on microbial food web may compete nutrients with PNF and show chemical defense against predators of HNF and ciliates. And the influence of A. sanguinea on the organisms within microbial food web was mainly due to its edible by HNF. The effects of S. costatum on microbial food web were modulated by nutrients and bacteria may play an important role in nutrient regeneration during lysis phase.