The coral ecosystem of this globe area escapes the whitening caused by the increase in water temperature, due to a very old natural selection phenomenon. Hope for scientists.
by Chloé Sartena
“It’s fabulous. There are even more colors than at Seychelles!” Said Oscar Fernandez, the sparkling look. This young Spaniard spends his holiday week exploring the reef located at the foot of the diving center of Marsa Shagra, Egypt. In the waters of the Marsa Alam coast, which covers almost 250 kilometers in the south-east of the country, a Kaleidoscopic ecosystem is full of life. Raies Eagles and Pastenagues tu depths when, a few meters below the surface, Angers or Clowns huddled in anemones, slide between the gorgonians, peck the many coral polyps with multiple shades.
A coral is made up of polyps, small marine invertebrates who live in symbiosis with an algae, the zooxanthelle, which provides food with food by photosynthesis. Too high a water temperature leads to the separation of coral and algae. And, in the absence of the seaweed, which gives it its color, the coral whitens.
Specialists in the intergovernmental group of experts on climate evolution believe that, in a world warmed of 2 ° C, from 90 % to 95 % of coral reefs, which house 33 % of marine species and provide their means Submint to half a billion people around the world, will die. Already, between 2009 and 2018, 14 % of the corals on the planet died.
While temperatures in the Red Sea are gradually warming towards the Gulf of Aden and its waters, in general, warm up at a higher pace (0.5 ° C per decade) to that of The global trend (around 0.3 ° C), the ecosystem of reefs of this sea – one of the longest in the world with its 4,500 kilometers of coast – resists this whitening.
Maximum Ice
A phenomenon linked to a form of natural thermal selection dating from the last glacial maximum, around 20,000 years ago. The glacial caps were thickened, the level of the seas came down. Shallow, the Strait of Bab-el-Mandeb, at the entrance to the Gulf of Aden, then isolated the Red Sea of the Indian Ocean, transforming it into a lake. “About 8,000 years ago, sea level went up, the water was able to cross the strait again. Due to its shallow depth, the water was very hot, between 33 ° C and 34 ° C . Only coral larvae resistant to this high temperature were able to cross this strait, which acted as a barrier, “explains Maoz Fine, Israeli researcher from the Institute of Marine Sciences of Eilat.
Today, in the north of the Red Sea, the maximum water temperature in summer is 27.2 ° C: these species therefore live well below their maximum physiological. “During laboratory simulations on the most resistant genres such as porites or stylophora, we even see that, up to 32 ° C, their metabolism works better,” continues Mr. Fine.
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