Scientists have unveiled the most comprehensive analysis ever undertaken of the world’s ocean plankton, the tiny organisms that serve as food for marine creatures such as the blue whale, but also provide half the oxygen we breathe.

The international team of researchers spent three and a half years aboard the schooner Tara, taking 35,000 samples of plankton from 210 sites globally, determining the distribution of the organisms, tracking how they interact with one another and carrying out genetic analyses.

Plankton include microscopic plants and animals, fish larvae, bacteria, viruses and other microorganisms that drift in the oceans.

“Plankton are much more than just food for the whales,” says Chris Bowler, a research director at France’s National Centre for Scientific Research, and one of the scientists involved in the studies published in Science today.

“Although tiny, these organisms are a vital part of the Earth’s life support system, providing half of the oxygen generated each year on Earth by photosynthesis and lying at the base of marine food chains on which all other ocean life depends.”

By removing carbon dioxide from the atmosphere and converting it into organic carbon via photosynthesis, plankton provide a buffer against the increased carbon dioxide being generated by the burning of fossil fuels, Bowler says.

The scientists conducted the largest DNA sequencing effort ever done in ocean science, pinpointing around 40 million plankton genes, most previously unknown.