Garza, D.R. and C.A. Suttle. 1996. Seasonal light effects on cyanophage communities. Eos 76(3 suppl):OS208.

Viruses which cause lysis of Synechococcus sp. are present throughout the year in the western Gulf of Mexico and may be responsible for significant mortality. Previous studies have measured the decay rates of virus isolates and have used this information to estimate the impact of viral pathogens on bacteria and phytoplankton communities. Decay rates of infectivity of natural cyanophage communities, in the presence and absence of the natural Synechococcus community, as well as the decay rates of cyanophage isolates were measured throughout the year. Solar-mediated decay of infectivity at the air/water interface of natural virus communities in UV-transparent bags ranged from undetectable to 0.335h^-1, with the highest rates generally occurring during the summer. Decay rates of the cyanophage isolates SPWM-1 and SPWM-3 (Cyanomyoviridae) were similar in the spring but were up to 2.5x greater than those of the natural community. These results indicate that the natural cyanophage communities in the summer are more resistant to damage by UV radiation than the cyanophage isolates, whereas the decay rates of the winter communities are similar to those of the isolates. This suggests that there is strong selective pressure for more UV resistant viruses in the summer. Moreover, decay rates of cyanophage infectivity were similar whether in the presence or absence of host cells, indicating that significant cyanophage production did not occur during the incubation period.