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Differential effects of temperature and salinity on viral production and lysis rates in South Australian waters


Viruses are the most common organism in the marine environment. They potentially infect all organisms and influence various biogeochemical and ecological processes, including nutrient cycling and bacterial and algal biodiversity and species distributions. Viruses are also a driving force in phytoplankton mortality, the lysis of these organisms having a significant impact on the microbial loop and potentially the entire marine food web. However, they are sensitive to a range of environmental stresses, which may affect both viral abundance and activity. Increases in viral abundance are in most cases directly related to the loss of their hosts, here heterotrophic bacteria and phytoplankton. Viral dynamics are influenced by a range of environmental parameters, in particular temperature and salinity that are both impacted by climate change and anthropogenic activities. While eukaryotic viruses are known to be temperature-dependant, nothing is known on fluctuations in temperature and/or salinity in relation to phytoplankton and bacteria phages. These changes may have significant effects on the viability of commercial fishing in regions of high sustainability. Increases in virulence may shut down the food web directly, via a significant loss of phytoplankton abundance, or indirectly, via the lysis of heterotrophic bacteria. In this context, we investigated the effects of temperature and salinity fluctuations on viral production and lysis rates and their relationship to phytoplankton population dynamics. This experiment has specifically been designed in an area where a high level of wild catch and aquaculture activity occurs, thus having strong ecological relevance.