Gaby Gorsky is not only one of the scientific coordinators of the Tara Oceans expedition, he is also an experienced Taranaut. When aboard Tara, he takes pleasure in transmitting knowledge. The opportunity came up again to ask him some questions about the relationships between different species of plankton.
The results of Tara Oceans are very important for understanding the planktonic world. After 3 years of collecting data in the world’s oceans, detailed mapping of plankton biodiversity has been established and the interactions between microorganisms were observed. Among the many interactions you have studied, you speak of collaboration and interdependence of planktonic species. What does that mean ?
Among the microscopic communities that are the basis of marine life and constitute a large part of the biodiversity of the ocean, we know that the planktonic species live in interactions relative to each other. Competition, cooperation, or symbiosis – their interactions are many. With the results of Tara Oceans, we’ve been able to demonstrate that the species have probably diversified through their collaborative relationship or their close interdependence. I think it’s this interdependence that plays a role in the diversification of species. It’s a hypothesis. In other words, when one species collaborates with another, if one is modified, it’s the whole set of “collaborators” that evolves. What we see from our results is that there are many more collaborations than we thought.
What is the best example of collaboration observed thanks to the Tara Oceans samples?
Many examples were presented in the articles we recently published in Science magazine. I’ll just mention a tapeworm living in symbiosis with algae that grow inside its body. These algae might just as well be considered symbionts as parasites. They can modify their reactions if a change occurs in their environment. They can, for example, begin to secrete toxins or other substances that could affect the life of the little worm.
You still have plenty of samples to be processed. What is becoming of this research?
With Tara Oceans, we were primarily collecting samples at sea. These samples were then analyzed on land because we were not equipped on board to do experiments (the boat is not big enough for this). We collected genes in the surface waters of the oceans we crossed – from 100 meters deep to the surface. As we continue the genetic studies and observe other samples, we’re not finding any new genes. We’ve arrived at the saturation point of our database. In other words, we’ve managed to collect the majority of the genes in the surface waters of the oceans. It’s fantastic !
We’ve also done a great deal of statistical work, including correlation studies. These correlations lead us to the associations of species I mentioned earlier. We’re working continuously: we collect, analyze, process and then propose hypotheses. We’ve already made good progress in our research on unicellular organisms, but we’ll need a little more time on the multicellular organisms which are far more complex, particularly in terms of relationships between species. Multicellular organisms harbor within their bodies, in their digestive tracts, a great diversity of symbiotic bacteria that help them digest their food. We’re currently working on this. The techniques take time, they are complex and each result must be verified. All information has to be double-checked.
Three years after the end of the Tara Oceans expedition, we’ve written 30 high-level scientific articles, and 5 of them were published in Science magazine. Very impressive! I’m at the end of my career, I’ve worked for 40 years in the field of oceanography and this is the first time I’ve seen such a thing. What we have done is unique.
Interview by Noëlie Pansiot
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