How did the blue crab become a threat to Corsica’s biodiversity?

In a few months, it became an emergency. in Callinectes sapidus invades the Corsican coast and especially the eastern part of the island, at least from what we know at the moment. “From northern Bastia to the extreme south of the region, they are everywhere, laments Marie Garrido, project manager at the Corsican Environment Office. We know that there is also west from Bonifacio to Figari, but nothing beyond that. There is no information, and we ask ourselves many questions.

The distribution of the blue crab, unlike its cousin in Tunisia, is not an ideal opportunity for over-trade. It is a nuisance nester, a formidable predator that threatens aquatic biodiversity and destroys fishing gear in affected lagoons. “It is an adaptive invasive species that is constantly progressing, that adapts very easily and quickly to environmental conditions, details of Marie Garrido. We know 70 species of this type in the Corsican Sea, but it is aggressive, omnivorous and hypertolerant to temperature fluctuations, oxygen…”

A real poison, completely unknown a few years ago. If the first report about the blue crab dates back to 1990, then only in 2014 in the Bigulya Nature Reserve was it really reported about its presence. “Until last year, we thought we had seen it for the first time in Corsica, explains a member of the environmental office. But after conducting research, we realized that we had already caught him before and that he was simply not the subject of feedback from scientific bodies.

An important meeting this Monday in Bastia
However, even in 2018, the censuses were still too scattered in time and quantity for the University of Corsica to study this topic. Concerns began to grow about the situation in Spain, where numbers in the Ebro Delta were becoming very critical. “We had to take the initiative to limit the impact on biodiversity or the functioning of the lagoons– says Marie Garrido. In early 2021, the task force developed a strategic action plan to detect the presence of crabs in the lagoons at an early stage.
Obligation to bring it to working condition, so as not to end up in a dramatic situation, as Occitania recently experienced. “In Caen-en-Roussillon, they did not notice that nothing would happen, the project manager observes. They only had a few individuals, and then their population tripled in three years.” The number of blue crabs weighing between 5 and 15 tons has raised fears of an invasion of all the surrounding lagoons.
So, to curb the phenomenon in Corsica, we had to increase our speed. On Monday, September 19, the Regional Committee for Sea Fisheries and Marine Economy (CRPMEM) in Bastia hosted a major meeting, which brought together organizations and participants in the sector. He was originally programmed to take the lead and think about better equipping professional fishermen in a lagoon environment. But with the latest figures for the summer period, the situation has changed.

Act while searching
At this meeting, it became known that to fight the invasion of this species, which lives on the coast of the Atlantic Ocean, it is necessary to act urgently. “We really need to be ready by June 2023 to start a targeted catch of Callinectes sapidus, while simultaneously conducting scientific activities, says Marie Garrido. The difficulty is, for example, in setting the right number of nets so that they are effective without affecting biodiversity.”
All agree that helping the sector, particularly with more reliable machinery, is a must. The participation of the University of Corsica is important from a scientific point of view due to the recommendations and opinions it can provide. “We do not want to rush events, aware of the urgency“, – assures the project manager in the office of environment of Corsica.
Bigulia and Palu districts were identified as priority for intervention. “We really have to try to control this population at the level of these lagoons that are most affected by reproduction, justifies Marie Garrido. At the moment, the priority is these two territories and the fishermen who work there.”

Pending new figures, the next meeting will be held in October to continue the discussion.

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