Lionfish, rabbitfish, blue crab… these invasive species are developing with the warming of the Mediterranean and disrupting its balance

Marine heat waves, a consequence of climate change, weigh on native species but are beneficial to other species from elsewhere that are more resistant.

The Mediterranean Sea is overheating. On Thursday, August 15, it broke a new median temperature record of 28.9°C, which is higher than in July 2023 when it reached 28.71°C, according to figures from the Institute of Marine Sciences (ICM) in Barcelona and the Catalan institute Icatmar. These marine heatwaves are catastrophic for many species that suffocate, such as gorgonians, large colorful corals. But at the same time, this heat benefits invasive species. The hotter it is, the better they develop, which disrupts the entire underwater ecosystem. There are more than a thousand of them in the Mediterranean, but only a handful cause major problems.

Among them, the lionfish, venomous with its white and orange stripes, it is almost at the top of the food chain. But also the rabbitfish, green and white, nicknamed the “lawnmower” which nibbles the algae forests. These two species disrupt the balance of the Mediterranean.“It disrupts the animal and plant communities because some of the species that enter the Mediterranean are extremely competitiveexplains Jean-Pierre Gattuso, oceanologist at the CNRS. And so the species that are in competition, the natives, can see their abundance decrease.”

“For example, in the case of herbivores, the rabbitfish will have eaten all the algae around and there is nothing left for the native species.”

Jean-Pierre Gattuso, oceanologist at the CNRS

to franceinfo

These invasive fish arrived from the Red Sea via the Suez Canal and are gaining ground due to global warming. Unlike local species, they are not weakened by marine heatwaves. “It’s a godsend, confirms oceanologist Jean-Pierre Gattuso. “We must relate these invasive species to the gradual warming of temperatures. It is not particularly the extreme values ​​that bring them in, it is the temperature of the Mediterranean which is increasing regularly.”

The blue crab is another of these problematic invasive species. It came from North America but is very comfortable in warm waters. It swarms on the coasts and lagoons of the Mediterranean, tears fishermen’s nets and devours other fish. So to get rid of it, why not eat it? Tunisia, for example, has set up a sector to market this crab.

“From the blue crab, we moved on to the crab with golden claws”

Nathalie Hilmi, environmental economist at the Monaco Scientific Center

to franceinfo

“In fact, they have created an industry around this new blue crab, explains Nathalie Hilmi, environmental economist at the Scientific Centre of Monaco, and they are now able to not only fish it and consume it locally, but also freeze it and export it, particularly to Asia.” The blue crab now represents a quarter of Tunisian fish and shellfish exports. The economy is therefore dependent on this invasive species, and quotas have even been put in place to prevent it from disappearing due to overfishing.