Major viral impact on the functioning of benthic deep-sea ecosystems

Viruses are the most abundant biological organisms of the world's oceans. Viral infections are a substantial source of mortality in a range of organisms - including autotrophic and heterotrophic plankton - but their impact on the deep ocean and benthic biosphere is completely unknown. Here we report that viral production in deep- sea benthic ecosystems worldwide is extremely high, and that viral infections are responsible for the abatement of 80% of prokaryotic heterotrophic production. Virus- induced prokaryotic mortality increases with increasing water depth, and beneath a depth of 1,000 m nearly all of the prokaryotic heterotrophic production is transformed into organic detritus. The viral shunt, releasing on a global scale similar to 0.37 - 0.63 gigatonnes of carbon per year, is an essential source of labile organic detritus in the deep- sea ecosystems. This process sustains a high prokaryotic biomass and provides an important contribution to prokaryotic metabolism, allowing the system to cope with the severe organic resource limitation of deep- sea ecosystems. Our results indicate that viruses have an important role in global biogeochemical cycles, in deep- sea metabolism and the overall functioning of the largest ecosystem of our biosphere.