台灣沿岸海域 2011 年夏季期間四個月份，利用修改後的稀釋培養法同時測量由病毒裂解與原生動物攝食所引起的 Synechococcus spp. 死亡率之日夜變化實驗。研究期間 Synechococcus spp. 的數量變化有明顯的日夜週期變化，其變化範圍從早上八點的 1.2 × 10^4 cells ml−1 至午夜期間的高值 9.8 × 10^4 cells ml−1。細胞分裂頻度的高值出現在下午至黃昏間，且在夜晚 20:00 至隔日早上 08:00 下降至<10 ％ 以內。研究期間 Synechococcus spp. 分別在白天和夜晚有不同的生長速率，分別是 0.025 至 0.033 h-1 和 0.050 至 0.085 h-1 之間。在白天和夜晚的微細鞭毛蟲的攝食率的平均速率分別是 0.041 h-1 和 0.031 h-1。由病毒裂解引起的死亡率在白天與夜晚分別是 0.011 至 0.019 h-1 與 0.026 至 0.065 h-1 之間。白天 Synechococcus spp. 的死亡率主要是由微細鞭毛蟲的攝食所控制;然而由病毒裂解與微細鞭毛蟲的攝食所引起的死亡率在夜晚期間兩者對 Synechococcus spp. 數量的影響非常相當。 Diel variations in the protozoan grazing and viral-mediated mortality of Synechococcus spp. were simultaneously estimated using a modified dilution method in the coastal waters off Taiwan during 4 cruises in summer 2011. During the study period, the abundance of Synechococcus spp. showed a clear diel cycle and ranged from 1.2 × 10^4 cells ml−1 at 08:00 h to 9.8 × 10^4 cells ml−1 at midnight. The frequency of dividing cell (FDC) values were highest between afternoon and dusk and decreased to <10% between 20:00 and 08:00 h. Synechococcus spp. specific growth rates varied during the experimental period from 0.025 to 0.033 h−1 and 0.050 to 0.085 h−1 at daytime and nighttime, respectively. Rates of Synechococcus spp. mortality due to nanoflagellate grazing averaged 0.031 h−1 during daytime and 0.041 h−1 at night. The estimated mortality due to viral lysis was between 0.011 and 0.019 h−1 during daytime and between 0.026 and 0.065 h−1 at night. Nanoflagellate grazing was the dominant cause of Synechococcus spp. mortality during daytime; however, mortality from viral lysis and nanoflagellate grazing was more balanced at night.