Hundreds of thousands of viruses found in oceans

The oceans contain almost 200,000 different viral populations, according to the latest count.

Marine viruses were found from the surface down to 4,000m deep and from the North to the South Pole.

Though most are harmless to humans, they can infect marine life, including whales and crustaceans, BBC News reports.

And scientists are only just starting to understand how these tiny organisms play a role in the life and chemistry of the seas.

Researchers at Ohio State University drew up a global map of marine viruses based on seawater samples from nearly 80 sites around the world. Their viral tally is almost 12-fold higher than previous estimates.

They were surprised to find that the viruses fell into just five groups based on their location and depth.

"When we examined the genes of the viruses in each of those communities, we found evidence of genetic adaptation to the different zones of the ocean," said researcher Ann Gregory, now of KU Leuven in Belgium.

The second surprise was that the Arctic Ocean had lots of different types of viruses. It had been thought that hotspots for microbial diversity would be at the equator.