The Mediterranean becomes a tropical sea

You are about to read the first part of our survey “ The coast, from paradise to climate nightmare “. The second one will come out tomorrow.

Flute fish in lemon shallot sauce, wingfish ceviche and patacones (fried bananas), chowder with ravioli stuffed with rabbit fish… The recipes for these exotic species are not taken from an advertisement for some tropical destination. Produced by the Ecoseas laboratory, they are available on the Université d’Azur website to raise public awareness of new species in Mediterranean waters. Even in order to encourage their consumption and even more so to fight against their distribution.

Under his cute nickname, the rabbit is the plague. Hailing from the Red Sea, this fish, which gets its name from its bulging mouth and tendency to reproduce rapidly, is an invasive species of concern. This small herbivorous fish looks like nothing, but it is so voracious and prolific that schools of rabbits destroy the sea grass and the many species that live there. »– says Virginie Raybaud, a marine ecology researcher at Ecoseas.

Rabbit, type voracious “. © Patrice Francour

First spotted in France in 2008, it has not yet been rampant on the French coast. Siganus luridusLatin name, on the other hand, is already responsible for the ecological disaster in the eastern Mediterranean, where there really isn’t much left to eat: the rabbitfish today represents 70 The % of species caught in Lebanon is specified by an expert.

1000 exotic species

Rabbit meat is not interestingnotes Virginie Raybaud, unlike a very thin lionfish. » This scorpion fish, which lives in the Red Sea, is also under the attention of all marine ecologists. The lionfish is a formidable predator in the Eastern Mediterranean, where its population has grown rapidly since 2012. Other tropical species currently seen in the Eastern Mediterranean are the flute fish or puffer fish. This cousin of puffer fish, a genus known to cause very serious tetrodotoxin poisoning, is already responsible for fatal poisonings in the Mediterranean.

Flute fish. Wikimedia Commons/CC BY 2.0/Ricard Zerpe

With its warmer waters, the eastern Mediterranean offers us a mirror of what awaits our longitudes. According to Virginie Raybaud, who models the distribution of species under the influence of water warming, these invasive fish pose a serious threat in the coming years to the northwestern Mediterranean.

Samara. © Murat Draman

Going through the research, all tropical species seem to be harmful. Virginie Raybaud admits a bias: scientific work is mainly focused on problematic species. Not all alien species are invasive. The latter respond to certain characteristics, such as great plasticity of habitat and diet or even early puberty. Of the nearly 1,000 alien species found in the Mediterranean, many do not pose a threat to ecosystems.

The dolphin fish, for example, is now observed off the coast of France. It is difficult to understand how this little-studied tropical species is evolving, except that more and more anglers are showing their trophy in social networks. Dolphinfish are currently being observed in the Gulf of Lionconfirms Thierry Laugier, head of research at the Marbec laboratory, which studies marine biodiversity ecosystems. Several species originate from the coast of North Africa and are becoming more common on the coast of France, such as the barracuda. » Virginie Raybaud also mentions the peacocks she recently came across in large flocks during her dives.

Water heating

With water temperatures increasing by an average of 0.4 °C every ten years, the Mediterranean Sea is becoming an environment favorable for the development of tropical species. And the Suez Canal is the best gateway for all these organizations. Since its opening in 1869, several hundred have come from the Red Sea to join the Mediterranean. They are even adorned with the Lessepsian species name in honor of Ferdinand de Lesseps, the French engineer who dug the canal.

The views on both sides of the channel are very different because these environments were sealed until this discovery. And if colonization was limited by the colder waters of the Mediterranean, warming waters today favor their establishment », emphasizes Virginie Raybaud. A recent study shows that the establishment of non-native species in the Mediterranean has increased by 40 % of the decade.

What about the Straits of Gibraltar ? It is difficult for tropical species to get there because the cold waters near the Western Sahara create a physical barrier », explains Thierry Laugier. Other known origins are tropical species, stowaways or survivors of emptying aquariums at sea, or even both. Marine ecologists are really concerned about large luxury yachts suspected of dumping their aquariums overboard. In any case, that’s the hypothesis of researcher Paolo Guidetti when he came face to face with Zebrasoma xanthuruma blue-yellow coral fish during one of his dives, he says in a scientific publication.

Yellow-tailed acanthurium (Zebrasoma xanthurum). Wikimedia Commons/CC BYHER 3.0/Zoophoto !

Fish make up only a small part of tropical species, not counting algae, molluscs and crustaceans. Microalgae genus Gambirdiscus responsible for the guitar (or ciguatera), a disease that can be contracted in the tropics by eating certain coral fish, is gradually spreading through the Mediterranean from the southeast to the northwest. This tropical algae was identified in 2010 in Cyprus and Greece, and then five years ago in the Balearic Islands. », explains Thierry Laugier. This indicates that the ciguatoxin responsible for the scratches is not currently produced by tropical algae. According to a November 2020 scientific publication, the risk to health in the Mediterranean Sea remains low.

Without changing species

Lovers of delicious fish meat should not rejoice too quickly. The appearance of the dolphin fish on the shelves could well be accompanied by the disappearance of its royal relative. Favorable establishment of tropical species, warming water threatens endemic species. There are no species extinctions on our coasts yet, but the geographic range of some species is shrinking, such as a few, sea bream and sea bream. »says Virginie Raybaud.

Finally, will alien species save life in the Mediterranean? ? Researchers are quite cautious. Look at the damage caused by the rabbitfish or blue crab, voracious crustaceans that occasionally wreak havoc on our coastal ecosystems. Looking at the evolution of marine species in the long term, we do not observe any trade-off between endemic and exotic species that would allow the preservation of the ecosystem. »notes Paolo G. Albano, a paleobiologist at the Anton Dorn Zoological Station in Naples.

which concludes: Global warming is changing the environmental conditions in the warm parts of the Mediterranean so much that only tropical species can survive. If the native populations disappear, only exotic species will be able to effectively guarantee a certain functioning of the ecosystem, although radically different from the current functioning. »

The coast has been for many years and still one of the first French tourist destinations… Magnificent sandy beaches, Atlantic islands with crystal clear water, small coastal villages… Landscapes that make us dream and shape our image of summer. But until ? Because climate change may well turn those postcard dreams into a climate nightmare.

We will tell you about it in our summer series, which will be released from August 1 to 4, on the island of Noirmoutier, which is in danger of flooding, in the Mediterranean Sea, where you will soon have to swim among barracudas, and on the Côte d’Azur, where the ghost of fire roams.

The second part of this series will be released tomorrow. Subscribe to our newsletter so you don’t miss the next chapters.

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