With a water temperature up to 6.5 ° C higher than normal off the coast of Spain, France and Italy, the gorgonians and the posidonies die in mass, forcing fish and Crustaceans, already threatened by predators of tropical origin, to migrate.
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Are the Mediterranean Sea ecosystems inevitably in danger? This is what scientists begin to believe, in the light of marine heat waves that multiply in the great blue. This summer, the phenomenon is particularly worrying.
A 6.5 ° C differential compared to the seasonal normal was measured by satellite on July 19 off Marseille. It is since May, more than seventy days in accumulated, that the sea presents “very important temperature anomalies”, notes Samuel Somot, specialist in heat waves in the Mediterranean in Météo-France. This concerns the waters located between 0 and 20 meters deep, between the Balearic Islands and the Spanish Levant Coast, but also against the Côte d’Azur, in France, throughout the Italian boot, from the Liguria Sea Until the Gulf of Taranto, and all around Corsica.
These figures approach – or even exceed – the two previous records recorded in a recent past. That of intensity, observed on August 5, 2018 off Marseille, with a temperature of water higher 6.6 ° C to seasonal normal, and that of duration, with a heat wave which had extended, In 2003, from August 3 to September 2.
“In the atmosphere, a heat wave never lasts so long. In the sea, yes. On the French coasts, the phenomenon experienced peaks at the end of June, at the end of June and at the end of July, which should be followed by a New increase in early August, “said Météo-France expert. Opposite Marseille, the marine heat wave is “extremely intense”, with 28 ºC measured on July 19, instead of a seasonal average of 21.5 ºC. Opposite Bastia, it has been “continued since the end of May”, with a water temperature around 30 ºC. Same thing in Balearic.
more 1 ° C in twenty-seven years
“These marine heat waves are triggered during a lasting situation of high temperatures and stable conditions, a cloudless sun, calm winds. Surface water no longer moves and cold water of depth can no longer go up , Having greatly suffer corals, crustaceans, fish … “, explains Rubén del Campo, spokesperson for the National Agency for Spanish Meteorology. Until the first days of August, the thermostat effect of the Mediterranean – that is to say its ability to regulate external temperatures – could be annihilated: “Normally, in winter, the sea tempers the cold and in summer , she tempers warm. Right now, this is not the case, especially at night. “
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