Effect of increased pCO2 on phytoplankton–virus interactions

Atmospheric carbon dioxide (CO₂) has increased since the pre-industrial period and is predicted to continue to increase throughout the twenty-first century. The ocean is a sink for atmospheric CO₂ and increased CO₂ concentration will change the carbonate equilibrium of seawater and result in lower carbonate ion concentration and lower pH. This may affect the entire marine biota but in particular calcifying organisms. In this study we investigated the effect of increased CO₂ on the virus host interaction of Emiliania huxleyi as a calcifying organism and of Phaeocystis poucheti as a non- calcifying organism. Both algae were grown in laboratory controlled conditions under past (280 ppmv), present (350 ppmv) and future (700 ppmv) CO₂ concentrations with and without added virus. Increased CO₂ had a negative effect on the growth rate of P. pouchetii, but not of E. huxleyi. No impact was found on viral lysis of P. pouchetii while increased burst size and slightly delayed lysis was observed for E. huxleyi with increased CO₂. We conclude that this short time study could not confirm earlier reports and our hypothesis of a negative effect of high CO₂ on E. huxleyi growth and E. huxleyi virus production.