Suttle, C.A. and F. Chen. 1992. Mechanisms and rates of decay of marine viruses in seawater. Applied and Environmental Microbiology 58:3721-3729.

Loss rates and loss processes for viruses in coastal seawater from the Gulf of Mexico were estimated using three different marine bacteriophages. Decay rates in the absence of sunlight ranged from 0.009 to 0.028 h^-1, with different viruses decaying at different rates. In part, decay was attributed to adsorption by heat-labile particles, as viruses did not decay or decayed very slowly in 0.2-µm-filtered, autoclaved or ultracentrifuged seawater, but continued to decay in cyanide-treated seawater. Cyanide did cause decay rates to decrease, however, indicating that biological processes were also involved. As decay rates were often greatly reduced in 0.8- or 1.0 µm-filtered seawater, whereas bacteria numbers were not, it suggested that most bacteria were not responsible for the decay. Decay rates were also reduced in 3-µm-filtered or cycloheximide-treated seawater, but not in 8-µm-filtered water, implying that flagellates consumed viruses. Viruses added to flagellate cultures decayed at 0.15 h^-1, corresponding to 3.3 viruses ingested flagellate^-1 h^-1. Infectivity was very sensitive to solar radiation and in full sunlight decay rates were 0.4-0.8 h^-1. Even when UV-B was blocked, rates were as high as 0.17 h^-1. Calculations suggest that in clear oceanic waters exposed to full sunlight that most of the viral decay, averaged over a depth of 200 m, would be attributable to solar radiation. In coastal waters, when decay rates were averaged over 24 h and 10 m depth, loss rates of infectivity attributable to sunlight were similar to those resulting from all other processes combined. Consequently, there should be a strong diel signal in the concentration of infectious viruses. In addition, as sunlight destroys infectivity but does not remove virus particles, a large proportion of the viruses in seawater are probably not infective.