Virus-like particles in a summer bloom of Emiliania huxleyi in the North Sea

The importance of viruses in controlling a bloom of the coccolithophorid Emiliania huxleyi in the North Sea was investigated during summer 1993. Viral infection of E. huxleyi was highest in the decaying phase of the bloom. Up to 50% of E. huxleyi cells were visibly infected. For E, huxleyi, 2 types of virus-like particles are reported. They differed in size and were occassionally found within the same cell. The infection level of the large virus-like particles was never higher than 25%. Viral lysis of E, huxleyi within the nitrogen-limited decaying phase of the bloom seemed an important source of organic carbon utilized by bacteria. In addition to infection in E. huxleyi, we also found severe viral infection in Chrysochromulina sp. Our results show that in natural ecosystems viruses can be a significant source of phytoplankton mortality, influencing phytoplankton (bloom) dynamics and the microbial food web.