Life began in the sea and continues to flourish there, undetected by modern science and invisible to the human eye—until now. A new survey of the waters that cover more than 70 percent of our planet has captured an unprecedented look at the teeming life of the global ocean, from 50-nanometer-wide viruses to fish that measure just a few millimeters in length.

© A. Deniaud/Tara Expeditions

The 36-meter research schooner Tara surveyed the oceans from 2009 to 2013 and stopped at more than 210 stations from the Arctic to the South Atlantic.

© bepoles/TaraExpeditions

The research ship took more than 35,000 samples with an array of tools, including seven different kinds of nets, towed either behind the vessel or dropped to depth of as much as 1,000 meters.

© V. Hilaire/Tara Expeditions

© Wedodata/Tara Expeditions

Using modern gene-sequencing techniques to puzzle out novel life forms, analyses of the expedition's data has been published in five different papers in the May 22 Science. One study revealed genetics from thousands of new viruses. "There is an unknown world of viruses that dominate our oceans," says marine biologist Jennifer Brum of the University of Arizona in Tucson, noting that although the dominant type of virus varies from location to location, the same viruses are present all over the world. "Everything is everywhere, but the environment selects," she observes.

© Science

Analyzing the DNA of marine microbes, the researchers found that there is not as much difference between oceanic genes and the genes present in the microbes that inhabit the human gut, although there are roughly four times as many different kinds of genes in the oceans. "It took me by surprise that there was a huge overlap of core functions between the two environments," says cell biologist Shinichi Sunagawa of the European Molecular Biology Laboratory (EMBL).

© Christian Sardet/CNRS/Tara Expeditions

At the same time, the survey found more novel genes from tiny parasitic and symbiotic animals in the sea than even in viruses. The researchers report discovery of roughly 150,000 novel versions of two particular stretches of DNA in the ribosome detected in the billion or so of these genetic bar codes collected, compared with 11,200 or so that had been previously described by scientists. This bounty of newly identified life-forms includes organisms ranging from single-celled protists to giant parasites, most previously unknown.

© Christian Sardet/CNRS/Tara Expeditions

This small animal known as a medusa collected in the Mediterranean is a relative of a jellyfish species whose members are thought to be immortal.

The survey data also suggests ocean organisms that work together to thrive, such as colonial radiolarians living within giant algae, are more numerous than those that directly compete. For example, brilliantly reflective Sapphirina copepods are carried through the ocean on salp hosts while consuming microscopic plants known as phytoplankton—the two simple animals cooperate to survive.

© Christian Sardet/CNRS/Sharif Mirshak/Parafilms/Tara Expeditions

"Competition is less important than collaboration" in determining which organisms thrive, says cell biologist Eric Karsenti of EMBL and France's National Center for Scientific Research (CNRS) who directed the Tara Oceans expedition. "It's not only survival of the fittest but also how everybody collaborates with everybody else that makes life evolve and become more complex."

The sea also hosts numerous parasites such as this amphipod that feeds on salps and then uses their empty husks as protective shells for itself.

© M. Ormestad/Kahikai/Tara Oceans

At the base of the food web, microscopic plants known collectively as phytoplankton are responsible for producing an estimated half of the oxygen in the atmosphere. One such phytoplankton is Lauderia annulata, from the Indian Ocean. Measuring some 200 microns across, it is one of the largest diatoms in the sea. This microscopic ocean plant turns sunlight into food in the tiny yellow and green particles known as chloroplasts that are encased within its cylindrical shell of glass.

© Christian Sardet/CNRS/Tara Expeditions

The far-reaching data, including a new oceanic genetic catalogue, will continue to be analyzed but one worrying fact is already apparent. The biggest factor that affects surface ocean microbes is temperature, and it is clear that the ocean is warming as it absorbs the excess heat trapped by the extra atmospheric carbon dioxide added by human fossil-fuel burning. "What exactly and how large this impact will be will require more data," Sunagawa says. But researchers are certain that this warming will affect the food chain that extends from microbes all the way up to mighty blue whales. It will also affect the cycling of elements—carbon, nitrogen and the oxygen we breathe.

"Plankton are much more than just food for whales," says plant biologist Chris Bowler of CNRS. "Thanks to the treasures from Tara's hauls, life in the oceans is a little less murky."