Coral reefs: who are they? that they may? – ladepeche.fr

The coral reefs that Tara Pacific left to study on Saturday in the Pacific, are beings “mi animal mi plant” at risk big to climate change.

“The corals are not simple animals, but complex organisms, “said Denis Allemand of the Monaco scientific Centre and co-director of Tara Pacific during a press conference. No fewer than 1,400 different species have already been identified.

These marine animals, composed of hundreds or even thousands of polyps, are of the same family as jellyfish, anemones and gorgonian sea. They are just as sophisticated as other animals. “The complexity of the genome of corals is as important as that of vertebrates,” said Denis German.

Many organizations called symbionts — microalgae or zooxanthellae, fungi, protists, viruses — live inside coral colonies.

The zooxanthellae provide corals with nutrients and give it its beautiful colors. In exchange, corals provide the algae carbon dioxide necessary for photosynthesis.

While the coral and algae growing together for a little over two hundred million years, they are now threatened by climate change.

So about 20% of reefs are already destroyed 15% risk of being by ten years and not less than 20% are threatened by 40 years.

the main cause of this disappearance: the increase in the surface temperature of the ocean that causes a separation between the animal and algae

“an increase in the. order of 0.5 to 1 degree sufficient to cause a cataclysmic phenomenon called bleaching, “explains Denis German.

butterfly Effect

When the coral suffers stress due to the temperature increase, for defense, it expels its algae.

“At the expense of its survival since these algae feed on,” said Serge Planes, one of French coral specialists, scientific director of the Tara.

If these events last only a few hours to a few days, the coral recovers algae in the marine environment and regains all its capacities but if the phenomenon continues, it dies.

“Tara will study whether a past bleaching will affect the current resistance of coral, “said German Denis.

“We have some clues that lead us to believe that it may be the case, but this is still debated,” he added. “As for the mechanism that underlies this increased resistance, it does not know at all”

Another major threat to these colorful animals. Ocean acidification caused by the absorption in the sea the CO2 produced by human activities.

Only a few species of corals are tolerant to more acidic oceans, many may disappear, resulting in decreased diversity.

Tara will travel including Japan whose sea owns natural CO2 sources, to different degrees of acidity.

the expedition will “use these sources whose pH can be very different to better study the adaptation of corals in these extreme environments” says Serge Planes.

Ultimately, the corals will also be faced with another problem, this one, the rising waters. But this is a problem in the longer term.

So the coral reef grows 1 to 4 mm per year when the increase of the sea level is she from 6 to 9 mm. Corals thus will gradually move away from the surface of the water and at the same time, light.

Now “to photosynthesis, algae, corals must live near the surface water, less than 20 meters, “said Denis Allemand

And that’s the butterfly effect. the absence of photosynthesis being synonymous with diet to marine animals. Car “by zooxanthellae photosynthesis produce sugar more than 95% feed the corals,” explains the researcher.