Gargantuan whales and hefty cephalopods are typically thought of as the classic marine mammoths, but they might have to make way for the mighty microbes, which constitute 50 to 90 percent of the oceans' total biomass, according to newly released data.

These tiny creatures can join together to create some of the largest masses of life on the planet, and researchers working on the decade-long Census of Marine Life project found one such seafloor mat off the Pacific coast of South America that is roughly the size of Greece.

A single liter of seawater, once thought to contain about 100,000 microbes, can actually hold more than one billion microorganisms, the census scientists reported. But these small creatures don't just live in the water column or on the seafloor. Large communities of microscopic animals have even been discovered more than one thousand meters beneath the seafloor. Some of these deep burrowers, such as loriciferans, are only a quarter of a millimeter long.

"Far from being a lifeless desert, the deep sea rivals such highly diverse ecosystems as tropical rainforests and coral reefs," Pedro Martinez Arbizu, of the German Center for Marine Biodiversity Research and leader of the Census of the Diversity of Abyssal Marine Life, said in a prepared statement.

Thanks to high-throughput DNA sequencing, researchers have been able to vastly expand their catalogue of marine microbes. "Scientists are discovering and describing an astonishing new world of marine microbial diversity and abundance," Mitch Sogin, of the Marine Biological Laboratory in Woods Hole and leader of the International Census of Marine Microbes, said in a prepared statement.

This genetic data has revealed that there might be as many as 100 times more microbe genera than researchers had assumed. One study conducted in the English Channel landed 7,000 new genera alone. Current estimates place the number of marine microbial species at about a billion, according to a prepared statement by John Baross of the University of Washington and chair of the International Census of Marine Microbes's scientific advisory council.

And research has yet to plumb the guts and surfaces of more macro ocean life, which, like humans, can play host to billions of microbial cells. The species living on and in "marine animals alone may account for hundreds of millions of microbial species," Baross said. "This is a huge frontier for the next decade."

Despite their small individual size, microbes play a big role in the oceans—and the planet overall. Microbes help to turn atmospheric carbon dioxide into usable carbon, completing about 95 percent of all respiration in the Earth's oceans. Even those deep in the seafloor, such as the deep-sea burrowers, "help oxygenate sediments and interact with microbes to cycle nutrients and carbon on the ocean floor," Arbizu said. But little is known about these creatures' susceptibility to the changes in ocean temperatures, dissolved gasses and acid levels that are predicted to occur with climate change.

"Tracking and visualizing such complex populations was impossible 10 years ago," Baross said. "Sequencing allows us to give the equivalent of an Internet URL to millions of microbes, to which we can attach all kinds of other information, like their favorite temperature and amount of salt and light."

The full findings of the census will be presented in October in London. For the coming decade Baross suggests a survey of marine viruses.

Image of loricciferan Culexiregiloricus trichiscalida, which was discovered off the coast of Africa some 4,100 meters below the surface last year through the census, courtesy of Gunnar Gad/Marco Buntzow/German Center for Marine Biodiversity Research/Census of Marine Life