Minuscule viruses on the sea floor have a big impact on the marine ecosystem, a new study shows. The viruses infect simple microbes, known as prokaryotes, that form one of the lowest rungs in the food chain. Usually the nutrients and carbon contained in prokaryotes are used by the larger organisms that eat them, but something very different happens when prokaryotes are infected by viruses: the viruses burst the prokaryotes open and release their carbon and nutrients into the water column [New Scientist]. When these nutrients sink down to the ocean floor they’re consumed by other microbes, which then multiply and provide more hosts for the viruses.
Researchers long ago grasped that viruses on the sea surface play a Dr.-Jekyll-and-Mr.-Hyde role, killing biomass while at the same time sustaining it. Now, though, evidence has emerged that these tiny bacterial pathogens also carry out unsung work at the ocean depths — a dark, inhospitable, nutrient-poor place that counts as last great unexplored ecosystem on the planet [AFP]. Researchers say the newly discovered role of deep sea viruses may also play a critical role in the carbon cycle, as the decaying remnants of the burst microbes carry carbon, which is sequestered in the ocean depths.
For the study, presented in the journal Nature [subscription required], researchers hauled up sediment from relatively shallow depths of 595 feet all the way to the cold ocean bottom at 14,959 feet. Wherever they looked, they found billions of viruses in the top layer of sediment. News of this thriving viral world is only the latest revelation about the surprising amount of life deep underwater: Around one-tenth of Earth’s living biomass exists at the bottom of the ocean, despite cold temperatures, impenetrable darkness and intense pressure [Nature News].
While the study neatly explains the conjoined virus-and-microbe life cycle, it raises more questions than it answers in regards to the carbon cycle, the process by which carbon is recycled through the atmosphere, oceans, and living organisms. The discovery that there’s such a high degree of carbon production in deep sea environments means that researchers will now have to adapt their models of ocean functioning and how it contributes to the overall carbon cycle [The Scientist]. If scientists want to fully understand how carbon dioxide in the atmosphere is causing global warming, researchers suggest, they’ll have to factor in the teeming viral ecosystem in the watery deep.