Dynamics of diatom viruses on the western coast of Japan

Diatoms are prominent primary producers that play an important role in global carbon cycles. Diatom dynamics are, therefore, important for biogeochemistry, fisheries and earth science. Viral infection is now assumed to be one of the most significant factors affecting diatom dynamics. However, few studies, based on practical field data, have focused on the relationship between diatoms and viruses in natural waters. To elucidate on this relationship, we assessed the temporal change in the abundance of diatoms and their viruses on the western coast of Japan from 2004 to 2009. Three species of diatoms were used as hosts to enumerate viruses in water and sediment samples: Chaetoceros debilis, C. tenuissimus and C. salsugineum. Diatom viruses in the water column rapidly increased during C. debilis and C. tenuissimus blooms, maintaining a high abundance throughout the blooming period. These data suggest the potential importance of viruses in controlling the population dynamics of diatoms in natural environments. The number of viruses in sediments fluctuated considerably, even during non-blooming periods, which suggests that virus-infected diatom cells were supplied to the sediments from water-column populations throughout the year. This process might be an important strategy to reduce the impact of viruses on diatom populations. Because diatom populations are thought to have an intimate relationship with their viruses in natural waters, further studies of diatom dynamics should include the effects of viral infections.