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 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 Troublé 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.
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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."
(Reporting by Will Dunham. Editing by Andre Grenon)
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