This study aims to investigate the relative importance of nanoflagellate grazing and viral lysis for heterotrophic bacteria and Synechococcus spp. mortality in coastal waters of the north-eastern Taiwan. The results showed that viral lysis and nanoflagellate grazing are the main factors responsible for the mortality of heterotrophic bacteria, however, the presence of viruses had a positive effect on the Synechococcus spp. growth. Moreover, this study observed different growth responses between heterotrophic bacteria and Synechococcus spp. population by using the modified dilution approach. The results also showed that there was lower net growth rate of Synechococcus spp. in 30 kDa dilution series than that observed in 0.2 μm series. Furthermore, based on the results obtained from modified dilution approach, we can estimate that about 12.8 ng N L-1 h-1 and 2.8 ng P L-1 h-1 was released by nanoflagellate grazing. In addition, this study estimated that, during the process of viral lysis, locally recycled nutrients released about 224 ng N L-1 h-1 and 24.9 ng P L-1 h-1 in this system. Our findings suggest that due to viral lysis, substantial portion of the recycled nutrients required for Synechococcus spp. growth was supplied sufficiently, emphasizing the importance of the viral shunt, especially in oligotrophic regions.