“We are beginning to get an idea of the complexity of plankton diversity”

© N.LeBescot/Tara Expéditions

On the occasion of the Naples stopover, the Tara Oceans expedition (2009-2013)* was honored by the Zoological Station A. Dohrn, one of the laboratories involved in this great scientific adventure. It was no surprise then, to meet Francesca Benzoni, Chris Bowler and Daniele Iudicone, scientific coordinators of Tara Oceans. Englishman Chris Bowler agreed to reveal some information about the long-awaited results of this expedition.

What important event took place in Paris last week? 

The scientific coordinators of Tara Oceans met to present the data analysis of the 3-year expedition to members of our Scientific Advisory Board from Europe and the United States. These experts are invited every 2 years to monitor the progress of our research and give us their recommendations. They were very impressed with the originality, quality and speed of the analysis performed by the consortium on the mass of acquired data.

This meeting took place at a key moment: we had just sent 5 articles to scientific journals. They were written by several authors, which underlines the multidisciplinary approach of Tara Oceans. These articles must now be checked and verified by independent experts. This process is called ”peer review.”

One of the objectives of Tara Oceans concerns the identification of plankton. Today it’s thought that very few of these organisms are known. Is this one of the topics covered by these articles? 

Indeed, the results relate to, among other things, identifying the number of planktonic organisms in the different oceans of the world using a molecular methodology called “metabarcoding.” The numbers obtained using the samples from Tara Oceans probably represent the majority of existing organisms in the illuminated layer of oceans.

In fact, the further we advance in our research and the more samples we analyze, the more we’re finding the same organisms. This probably means that we have reached a saturation point; we’re beginning to get an idea of the complexity of plankton diversity.

We also made an estimate of the bacterial gene pool. This is one of the largest databases in terms of sequenced DNA, greater than that for the human genome. We also established a record of bacteria, viruses and protists present at each location, which will help us understand how these organisms interact with each other, their symbioses. We’ve found that these interactions are much more important than formerly thought, especially regarding parasitism. The interactions between different organisms are probably essential to the functioning of the planktonic ecosystem. Some organisms are more sensitive than others to rising temperatures due to climate change. Once impacted by this change, the planktonic system may cause blockages in the energy transfer to other predatory species, such as fish and so on. And all this could obviously have an impact on the functioning of the carbon pump which would be important to anticipate.

Interview by Noëlie Pansiot 

*Launched in September 2009, Tara’s 8th expedition (Tara Oceans) was conceived to identify, during a world tour of two and a half years and 50 stopovers, the effects of global warming on plankton and reef systems.

Related articles: 

- Interview with Cristina Fossi, professsor in ecotoxicology by Noëlie Pansiot. 

- Scientific objectives of Tara Oceans. 

- Gaby Gorsky, scientific father of Tara Mediterranean