The hidden world of the ocean's tiniest organisms has been revealed in a series of papers published in the journal Science.

 

An international team has been studying samples of plankton collected during a three-year global expedition.

 

They have so far found 35,000 species of bacteria, 5,000 new viruses and 150,000 single-celled plants and creatures.

 

They believe that the majority of these are new to science.

 

Dr. Chris Bowler, from the National Centre for Scientific Research (CNRS), in Paris, said: "We have the most complete description yet of planktonic organisms to date: what's there in terms of viruses, bacteria and protozoa - we finally have a catalogue of what is present globally."

 

Planktonic organisms are minute, but together they make up 90% of the mass of all of the marine life in the oceans.

 

They include viruses, bacteria, single-celled plants and creatures (protozoa).

 

They form the very base of the food chain, and produce - through photosynthesis - half of the oxygen we breathe.

 

However, until now, little has been known about this unseen ocean ecosystem.

 

The Tara expedition, primarily funded by the French fashion designer Agnes B, set out to change that.

 

An international team of scientists took part in expeditions onboard the Tara schooner between 2009 and 2013.

 

It sailed 30,000km across the world's oceans, with researchers collecting 35,000 samples, taking them from the very top layers of the ocean down to 1,000m below the waves.

 

The project has cost about 10 million Euros.