Virus. The word evokes images of illness and fears of outbreaks. Yet, in the oceans, not all viruses are bad news.Some play a helpful, even critical, role in sustaining marine life.In a new study, we and an international team of scientists examined the behavior of marine viruses in a large band of oxygen-rich water just under the surface of the Atlantic Ocean. What we discovered there – and its role in the food web – shows marine viruses in a new light.Studying something so tinyViruses are incredibly small, typically no more than tens of nanometers in diameter, nearly a hundred times smaller than a bacterium and more than a thousand times smaller than the width of a strand of hair.AdvertisementAdvertisementAdvertisementAdvertisementIn fact, viruses are so small that they cannot be seen using conventional microscopes.An electron microscope view shows examples of Prochlorococcus myoviruses. Images A and D show different viruses with their tails. In B and C, the tail is contracted. The black scale bar indicates a length of 100 nanometers. MB Sullivan, et al., 2005, PLOS One, CC BYDecades ago, scientists thought that marine viruses were neither abundant nor ecologically relevant, despite the clear relevance of viruses to humans, plants and animals.Then, advances in the use of transmission electron microscopes in the late 1980s changed everything. Scientists were able to examine sea water at a very high magnification and saw tiny, circular objects containing DNA. These were viruses, and there were tens of millions of them per milliliter of water – tens of thousands of times greater than had been estimated in the past.A theory for how viruses feed the marine worldMost marine viruses infect the cells of microorganisms – the bacteria and algae that serve as the base of the ocean food web and are responsible for about half the oxygen generated on the planet.AdvertisementAdvertisementAdvertisementAdvertisementBy the late 1990s, scientists realized that virus activity was likely shaping how carbon and nutrients cycled through ocean systems. We hypothesized, in what’s known as the viral shunt model, that the marine viruses break open the cells of microorganisms and release their carbon and nutrients into the water.This process could increase the amount of nutrients reaching marine phytoplankton. Phytoplankton provide food for krill and fish, which …
