Study Reveals Amazing Biodiversity of Pacific Coral Reef Microbiome

It is the largest bioconstruction on our planet and yet we continue to learn about it. We’re talking to you coral reefsthese living constructions formed by polypsthese animals that look like small jellyfish, and whose limestone skeletons gradually give rise to coral colonies visible from space.

And in there, it’s teeming with life, because these corals serve, depending on the species, as shelters, larders, nurseries… when it’s not all at once. “Over an area roughly equal to that of Germany, corals are home to 30% of marine biodiversity,” recalls Denis Allemand, scientific director of the Monaco Science Center and coral specialist. That is about 70,000 species. »

Two and a half years traveling the Pacific

Denis Allemand talks about marine animal and plant biodiversity. But if we go down the scale of the microbiome – or bacteria, viruses and other unicellular micro-organisms that live in symbiosis with coral reefs, like our microbiota to us humans – then the abundance of life is much greater still. And even more than imagined? A study published this Thursday in the scientific journal Kind Communication concludes that the diversity of the microbiome of Pacific coral reefs alone could reach a value close to the total diversity of microorganisms estimated so far on Earth.

This study is one of eight to be published this Thursday in scientific publications and to have the Tara Pacific expedition as its starting point. For two and a half years, from May 2016 to the end of October 2018, the schooner of the Tara Ocean Scientific Foundation crisscrossed the Pacific, from China to Panama, to try to discover the hidden diversity of coral reefs and better understand their ability to adapt to climate change. “In total, 58,000 samples were collected during nearly 4,000 scuba dives,” says Romain Troublé, executive director of Tara Ocean.

For two and a half years, from May 2016 to the end of October 2018, the Tara Océan scientific foundation schooner crisscrossed the Pacific, from China to Panama, to try to discover the hidden diversity of coral reefs – @TaraOcean

A “fascinating” diversity of micro-organisms

In the batch, more than 5,000 samples of three species of coral, two of fish and plankton in 99 different reefs, were the subject of genomic sequencing with a view, in particular, to listing and mapping the micro-organisms present. It is from this database that the team of Pierre Galland, director of research at Banyuls Oceanological Observatory (CNRS)a microbiology specialist, discovered “this enormous diversity of the microbiome in the reefs of the Pacific”.

“There were already initial estimates of the total number of species of microorganisms on the scale of the entire Earth, estimated at several million, begins the scientist. However, just with the several thousand samples collected within the framework of Tara Pacific, we already arrive at approximately 20% of this order of magnitude. And if we extrapolate our data to the hundreds of species of fish and coral found in the reefs of the Pacific, then the diversity of the Pacific microbiome is most certainly comparable to that which had been imagined for the whole globe. . »

An indicator of good coral health

This is one of the conclusions of this study: “the total number of micro-organisms on our planet could have been considerably underestimated”, resumes Pierre Galland. The scientist also makes this “fascinating diversity of the microbiome” one more reason to save these coral reefs, very vulnerable to the increase in mean ocean temperatureone of the consequences of climate change.

It remains to understand precisely the role of these bacteria and other micro-organisms in the functioning of these corals. The Tara Pacific mission has already made it possible to take steps in this direction. “We have discovered three new species of bacteria, each associated specifically with a species of coral, illustrates Pierre Galland. By studying the genome of these bacteria, we have been able to see that they produce vitamins, in particular the very important B vitamins, which they bring to the coral, which itself does not produce any. This is an example of the balance that operates between the bacteria and its coral, visibly since very ancient times, and which contributes to the good health of the reef, especially in the face of the stresses that affect it, including those linked to climate change. ..”

A world to discover

But in this area, research is still in its infancy. Pierre Galand and Denis Allemand draw a parallel with the human microbiota. “Although significant research resources have been allocated in this field, we are beginning to have a fairly precise idea of ​​its diversity. On the other hand, we continue to find new roles for it in human physiology,” explain the two scientists. For the coral microbiota, on the other hand, we are starting almost from scratch.

Pierre Galand already has a whole host of avenues in mind to explore. “How, for example, could these micro-organisms be used as indicators of the state of health of a coral reef, depending on the bacteria found there or, conversely, the imbalances what do we see? he illustrates. How also could we use these microbial communities as probioticscocktails of bacteria that we would inject into the reef to improve their health and/or their resistance to climate change?

Time is running out to explore this new world, as global warming continues to increase. Denis Allemand thus refers to the alert relayed in December 2020 from United Nations Environment Program (UNEP) on the possible disappearance of coral reefs by the end of the century, unless there is a drastic reduction in greenhouse gas emissions.

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