Plankton is not just whale food

Scientists on Thursday 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 researchers spent 3-1/2 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," said Chris Bowler, a research director at France's National Center for Scientific Research, and one of the scientists involved in the study published in the journal Science.

"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."

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

Much of the plankton was more genetically diverse than previously known. However, the genetic diversity of marine viruses was much lower than anticipated. 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 said.

Tara Expeditions Executive Director Romain Trouble said the schooner sailed about 87,000 miles (140,000 km) during the research voyage. Those aboard endured hardships such as being locked for 10 days in Arctic ice, storms in the Mediterranean Sea and in the Magellan Straight, and sailing through the Gulf of Aden with protection from the French navy against pirates. The scientists found that most of the interactions between plankton organisms were parasitic. They also found evidence for widespread dispersal of viruses in the oceans.

"Since the most numerous members of the plankton are bacteria, the majority of viruses in the ocean are thought to infect bacteria," University of Arizona oceanographer Jennifer Brum, another of the researchers, said.

"A good way of thinking about this is that there are roughly 200 million viruses in every mouthful of seawater, and most of those viruses are infecting the roughly 20 million bacteria found in every mouthful of seawater."