“ TARA OCEANS, A TREASURE FOR SCIENTISTS ”

Launched in September 2009, the schooner’s 8th expedition (Tara Oceans) has been a two and a half year voyage around the world, with fifty stopovers. Itspurpose has been to investigate planktonic and coral ecosystemsin the perspective of climate changes. One hundred international scientists have taken part. The initialresultsof the expedition have exceeded expectations. But it willtake many yearsfor the data to be analysed and the results published.

An odyssey totalling 938 days at sea, the expedition sailed from the Mediterranean to the Atlantic via the Indian Ocean, the Pacific and the Antarctic. Now that the end is in sight, the team can legitimately claim that the mission has been accomplished! Indeed 70 crew members and 126 scientists from 35 countries spent two and a half years working on the Tara for a common goal.

Co-directed by Eric Karsenti (the scientific director of the expedition and CNRS researcher), and Etienne Bourgois (owner and chairman of the Tara), the expedition has enjoyed the support of France’s National Centre for Scientific Research (CNRS), the European Molecular Biology Laboratory (EMBL), France’s Alternative Energies and Atomic Energy Commission (CEA) and many public and private organizations. The ambitions of the project have been clear from the outset: to study the mysterious plankton ecosystems in the world’s oceans in order to identify their precious genomes.
Plankton is a diverse group of drifting organisms that comprises plants, algae, viruses, bacteria and animals such as the giant jellyfish Cyanea Capillata whose tentacles can be up to 37 m long. The name plankton comes from the Greek planktos meaning “drifting”, “errant”. Eighty per cent of the single cell organisms which began to appear on earth more than 3 billion years ago are plankton and they play an essential role in the global climate and biogeochemical cycles. The project captured Eric Karsenti’s enthusiasm: “The idea was to improve our understanding of plankton, how it evolves, how it interconnects and moves constantly from one ocean to another. It is a complex subject and we have a lot of questions. How are micro-organisms distributed in the oceans and what is their biodiversity? We only know a tenth, perhaps a hundredth, of what there is to know. And what about the risks to plankton, the bacteria and the viruses? Are all these kingdoms linked and reliant on each other? In localized areas or everywhere? How many of them are there? What influence does temperature, salinity, acidity and physico-chemical parameters have on these strange creatures, and in which regions?” To answer these questions the Tara Oceans Expedition called on an army of experts who specialize in genomics, quantitative imaging, biology, biogeochemistry, biogeography, oceanography, biophysics, genetics and bioinformatics, and more. A rare meeting of disciplines. “That’s why this expedition is special, revolutionary. And it makes it essential too.”

In 1997, NASA published the world’s first estimate of how much chlorophyll is produced by plankton and went on to demonstrate its role in regulating our air through the process of photosynthesis. The Tara Oceans Expedition has added to our knowledge an avalanche of data collected at sea during the 150 sampling operations which started in 2009. Tara’s researchers took 27,000 samples, an exploit that represents a giant step in the field of the infinitely small. The expedition has discovered a panorama of plankton hitherto unknown. Despite the discovery of 500,000 new micro-organisms, “95% of them remain unknown,” says Eric Karsenti.
“Our bioinformatic methods have shown us that, from one sampling operation to the next, bacteria have incredibly diverse metabolic activities,” says Eric Karsenti. That is why the scientists considered it was essential for them to carry out ecosystem modelling, especially as the numerous sampling operations made it possible. “These kinds of models are essential. They can help us predict how the oceans are going to evolve, how their ecosystems are organized and distributed geographically. They are very useful in this era of sea acidification and global warming,” says Swiss-French biologist Colomban de Vargas, Protista specialist at the CNRS.
The Tara Oceans Expedition has enabled scientists to measure how marine life is responding to climate change. “The distribution of micro-organisms is in part determined by the environment, latitude and currents,” explains Eric Karsenti. “These models should help us predict how marine life is going to evolve in response to climate variation, the carbon cycle in both hemispheres and the overall regulation of the climate.”
“We noticed that the plankton was colonized by a large number of viruses and that it was adapting to the warming. It was continuing to produce its balanced quota of oxygen and CO2 and, therefore, continuing to play a role in reducing the greenhouse effect,” says Eric Karsenti. “We now have a more detailed view of its biodiversity and its complexity. Of the genes and bacilli analysed to date, 60 to 80 % of them were previously unknown to science. This data is of capital importance because any variation in the composition of the plankton can have an impact on the balance of the planet’s gases.”

GOOD BILL OF HEALTH FOR THE CORAL REEFS EXPLORED

Another of the expedition’s accomplished missions was to carry out a health check on coral ecosystems. In total 102 sites were studied off the coasts of Djibouti, Saint-Brandon, Mayotte and the Gambier Islands. A good state of health was observed on the coral reefs explored and they appeared to be resisting various thermal stresses and temperature increases. However the acidification of the oceans and the invasion of deadly starfish in certain regions is a worry. Samples collected by the Tara Oceans Expedition are currently being studied. The results will tell us if the coral can survive any future increase in temperature. The expedition also made other astounding discoveries, including one which was appalling. During the Tara’s passage through Antarctic waters in January 2011, she collected evidence of a surprising quantity of plastic in the area. The samples she collected contained between 956 and 42,826 pieces of plastic per square kilometre. These findings are of great consequence. Studies are being made into the risks that this pollution presents to the health of humans, animals, birds and marine mammals. Whether at sea or on land, on the Tara or in the lab: the expedition continues.

MAJOR DISCOVERIES

micro-organisms :
Coming soon, a new international base of data collected by the Tara to improve our understanding of how the world’s climate is regulated.

genomes :
An unexpected diversity was discovered in the plankton genomes, especially in phytoplankton.

fertilization of the oceans :
A great quantity of diverse samples were collected.
These are currently being analysed using imaging and genomic methods.

coral mission :
Dynamic coral populations were investigated and ten new species were discovered, notably in the Gambier Islands.