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 ecosys tems. They are especially vulnerable at the stage when they are free p articles 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 v ery high attenuation coefficient. Processes that move viruses to the s urface change their UV exposure. We have modelled the mortality of vir uses subject to UV radiation by means of a Lagrangian Monte-Carlo type model that incorporates viral movements within the mixed layer. For v iruses with a given UV-induced surface mortality, mixed-layer depth an d UV attenuation coefficient are important f actors in their water col umn mortality. Other more subtle factors can also affect viral mortali ty: nature of the diurnal thermocline; type of mixing; and the time of day that they are released into the water. Viruses not subject to mix ing have their mortality rate enhanced by internal wave motion, althou gh the absolute mortality rates may remain low. Increased UV irradianc e associated with atmospheric ozone depletion could significantly chan ge viral mortality in polar environments. UV-induced mortality can be comparable to that from biological factors such as virucidal bacteria.