With temperatures of up to 30°, the marine heat wave in the Mediterranean Sea could cause “massive mortality” in local fauna, explains Jean-Pierre Gattuso.
“The Mediterranean is becoming tropical“, said Friday, July 21 on franceinfo Jean-Pierre Gattuso, CNRS researcher at the Villefranche-sur-Mer Oceanography Laboratory (Alpes-Maritimes), while a marine heat wave affects the Mediterranean basin, with temperatures ranging up to 30 ° locally, with consequences on the fauna and flora. For Jean-Pierre Gattuso, two consecutive years in heat wave is “A suprise“. It warns about the “mass mortalities” of species observed and the appearance of “new predators” in Mediterranean.
>>> INFOGRAPHICS. Visualize the extent of the sea heat wave in the North Atlantic which threatens thousands of species.
franceinfo: Do these temperatures surprise and concern you?
Jean-Pierre Gattuso : For the scientific community, this is not a surprise. What is a surprise is the speed. We had an extremely intense heat wave in the Mediterranean last year, 134 days, with a record temperature of 29.1° in Villefranche-sur-Mer. So we can consider that the Mediterranean is tropicalizing. At 29°, it is typically a temperature encountered in the tropics. Of course, it goes down again in the winter. But even the winter temperature in the Mediterranean, which is roughly 13° on our coasts, is also increasing. Much slower, but it also increases. We end up with two consecutive years of heat waves, whereas previously these sea heat waves were spaced several years apart. So we have the impression of a runaway that surprises us. Italian colleagues reported much higher temperatures, 30°. This is unheard of in the Mediterranean.
“We observe these temperatures in the Arabo-Persian Gulf. But in the Mediterranean, it is absolutely unheard of. I hope that we will not get there because the consequences are really catastrophic.
Jean-Pierre Gattusoat franceinfo
What are these consequences?
First of all, there are massive mortalities. There are also movements of species, migrations. Species that can, that are mobile, move. For example, there is an influx of fish originating from temperate zones that come up in the Arctic or on the coasts of Iceland. So this is good news for these countries. On the other hand, this is very bad news for the intertropical zone, which is seeing its fish populations shrink more and more. There is a certain injustice because these are the countries that do not have much to do with climate change and they are the ones who pay the price first.
You talk about mortalities, the disappearance of certain species. At one, two or three degrees difference, can these species not survive in water?
Take the case of corals for example. They don’t all die 100%. When we talk about mass mortality, there are many individuals who die, but there are still a few, because they have the capacity to resist. But with the increase in the frequency and intensity of these marine heat waves, the following year there is still a fraction that will die, and the year after too. So we cannot envisage a real return to normal if the frequency of these events is too rapid.
Do we see, through migrations, species appear in certain marine areas that had never been there before?
Yes. We can cite the Mediterranean. There are about 1,000 species from the Red Sea that managed to settle in the Mediterranean through the Suez Canal. This is another manifestation of the tropicalization of the Mediterranean Sea, since the Red Sea is a tropical sea. Not all of them pose any problems, far from it, but some compete with species native to the Mediterranean. For example the rabbitfish, which is excessively voracious, which competes with other herbivorous fish. This makes new predators.