VIRAL DYNAMICS .2. A MODEL OF THE INTERACTION OF ULTRAVIOLET-LIGHT AND MIXING PROCESSES ON VIRUS SURVIVAL IN SEAWATER

Viruses are an important component in the functioning of marine ecosystems. They are especially vulnerable at the stage when they are free particles seeking a new host. A major factor in viral mortality during this phase is the presence of ultraviolet (UV) radiation. UV radiation penetrates only a short distance into the water column because of a very high attenuation coefficient. Processes that move viruses to the surface change their UV exposure. We have modelled the mortality of viruses subject to UV radiation by means of a Lagrangian Monte-Carlo type model that incorporates viral movements within the mixed layer. For viruses with a given UV-induced surface mortality, mixed-layer depth and UV attenuation coefficient are important f actors in their water column mortality. Other more subtle factors can also affect viral mortality: nature of the diurnal thermocline; type of mixing; and the time of day that they are released into the water. Viruses not subject to mixing have their mortality rate enhanced by internal wave motion, although the absolute mortality rates may remain low. Increased UV irradiance associated with atmospheric ozone depletion could significantly change viral mortality in polar environments. UV-induced mortality can be comparable to that from biological factors such as virucidal bacteria.