Initiated by the Tara Océan Foundation and its partners and coordinated by the CNRS, CEA and EMBL, the Tara Oceans expedition gathered 35,000 marine plankton samples and analyzed them in depth. Tara Oceans brought together more than 200 scientists from some 20 international laboratories, now associates within the Tara Oceans Research Federation.
A new study led by researchers from Ohio University, published in Cell on May 16, brings the number of known oceanic viral populations from 16,000 to nearly 200,000. Because these populations play a role particularly in transporting carbon from the surface to the seabed (the ‘biological pump’), it is essential to identify them and understand their functioning, dynamics and role in the ecosystem. The study has shed light on the genetic variation within each population, informing researchers about the evolution and impact of oceanic viruses on a global scale, and consolidated our understanding of marine virus populations.
First systematic study of the biodiversity of the Arctic Ocean
Run in collaboration with the countries bordering the Arctic Ocean, the work includes samples from the 2013 circumnavigation by the scientific schooner Tara of the edge of the Arctic ice pack, one of the regions most affected by climate change. It enabled the viruses to be
documented through analysis of their DNA. Data collection was extended beyond the Arctic Ocean to other oceans, and to greater depths than in previous studies[1].
Because these viruses have an impact on all marine planktonic organisms (bacteria, archaea, protists and animals), a detailed survey of them is extremely valuable. Viruses can alter the structure of bacterial populations by colonizing them, stimulating their metabolism, or modifying their evolutionary trajectory, affecting the ocean's overall capacity to sequester carbon from the atmosphere.
Marine planktonic microorganisms play a vital role on Earth: they produce more than half of the oxygen that we breath and absorb carbon dioxide from the atmosphere, transferring it to the ocean floor.
Accessing the genetic variation of viruses to understand their evolution
By developing new methods to sequence the genomes of these viruses within plankton populations, researchers were able to study genetic variations:
- between individuals within each viral population;
- between populations within each viral community;
- between communities across several global oceanic environments, as well as the driving forces behind these variations.
These world maps of viral diversity are surprising in that almost all viral communities are split into only five groups, according to their location and depth. The viral diversity measured in the Arctic Ocean is also surprising: most studies of unicellular and multicellular organisms have concluded that the greatest diversity is found in the tropics, and that it diminishes with proximity to the poles.
These new results suggest that the Arctic Ocean is a little-known 'cradle' of viral biodiversity. They highlight the importance of the Arctic regions, which are heavily impacted by climate change, for global biodiversity.
This study was supported notably by the Gordon and Betty Moore Foundation, the National Science Foundation and Oceanomics and France Génomique (French Investments for the Future program).
[1] Patterns and ecological drivers of ocean viral communities. J.R. Brum, J.C. Ignacio-Espinosa, S. Roux et al., Science, May 22, 2015. DOI: 10.1126/science.1261498
© Jennifer Brum and Matt B. Sullivan / Lab. Ohio State
[1] The Tara Oceans Research Federation, consisting of 22 French and international research teams, set up the GO-SEE (Global Oceans Systems Ecology & Evolution) program involving in particular the CNRS, CEA, Tara Océan Foundation, Sorbonne University, PSL, Inserm, ENS Paris, IRD, EPHE, Évry-Val d’Essonne University, Paris-Saclay University, UPVD, AMU, University of Toulon, École Centrale de Nantes, University of Nantes, UGA, EMBL and the Faculty of Physical and Mathematical Sciences at the University of Chile.