Preferential grazing of Oxyrrhis marina on virus-infected Emiliania huxleyi

We examined whether virus infection of Emiliania huxleyi with the lytic E. huxleyi-specific virus, EhV-86, influenced it's palatability to the heterotrophic dinoflagellate Oxyrrhis marina. E. huxleyi mortality was assessed by comparing changes in the algae's concentration between four different incubations: (1) Grazer O. marina plus an equal concentration of infected and healthy E. huxleyi prey (grazed-infected); (2) the same equal concentration of healthy and infected E. huxleyi prey without grazer O. marina (infected); (3) healthy E. huxleyi prey (no infected cells) with grazer O. marina (grazed); and (4) healthy E. huxleyi prey alone (no grazer or infected cells; control). Grazing rates of O. marina increased in the presence of virus-infected E. huxleyi prey. An adapted plaque assay protocol revealed that the amount of infected cells in grazed-infected cultures was approximately one-quarter (0.28) of that observed in infected (minus grazer) controls. Given that these assays were normalized to cell number, they demonstrate that O. marina was preferentially feeding on virus-infected E. huxleyi over their healthy counterparts. The effects of marine viruses may have been misinterpreted since the likelihood of them being grazed during infection has not been previously considered. Preferential grazing of infected cells in the ocean would sequester more carbon in particulate form, making it available to higher trophic levels. Consequently, these results should be taken into consideration when modeling the ocean carbon budget.