The blue crab is taking over the lagoons and it’s a disaster for the ecosystem

This blue crab is far from a dream. This particularly aggressive species invaded the lagoons of the Mediterranean arc with great speed. A native of the American Atlantic coast, this crab, introduced, according to the most probable hypothesis, by the ballast water of ships, flows smoothly into the ponds of the western part of the Gulf of Lion. In particular, the lagoon of Canet-en-Roussillon in the Eastern Pyrenees, which this species, capable of swimming 15 km per day, colonized on its way from Spain. Here it is the most, on the French side.

But she is also in love with the ponds of Lecate and La Palme, in Aude, and Tau, in Hérault. And attacks Corsica. In 2019 and 2020, several tons of this species, which has exceptional fertility, were harvested in Caen-en-Roussillon. In 2021, the catch exceeded 10 tons, according to Pascal Romans, head of the aquarium service at the Banyuls-sur-Mer Oceanological Observatory.

He unbalanced “the entire food chain” in Caen-en-Roussillon

The problem is that this crab, which can grow up to 23 cm in width, causes significant damage to these already extremely fragile ecosystems. First, he devours (almost) everything in his path. “The blue crab has an extremely diverse diet and has thrown the entire food chain out of balance,” explains Pascal Romans. Green crabs, fish, eels… He prepares them for lunch. “And we see that some birds are starting to fly away, because they probably don’t have food anymore,” the researcher continues.

This voracious blue-clawed crab is also a nightmare for anglers. “He has extremely sharp claws,” notes Pascal Romans. Classic grids, he makes crumbs. And the nets are a little more adapted, so he still manages to damage them. And the fish, the few that are left, run away. Jean-Claude Pons, one of the last eel fishermen on Canet Pond, hauled in kilos of blue crabs with his nets at the end of last year. “In December, I raised the last net, maybe 30 kg,” says the fisherman. We don’t know what to do anymore. »

Is this a problem for swimmers too?

The fear is that this supervillain will also destabilize the shellfish farming economy if it develops in Lecate or Tau ponds. Because oysters and mussels, blue crabs also love. “They break open mussels and eat them without any problems,” continues Pascal Romans. As for oysters, we know that they manage to open them up to half the size of an adult. A study was launched by the state and region of Occitania to try to limit their spread and support fishermen.

But aside from that, the blue crab can also be a problem for swimmers. Because his claws can cause serious injuries. “If you attack him, he won’t run away. He is extremely lively, notes Pascal Romans. And most importantly, his claws are so long that if you grab him from behind, he can catch you. He can break his finger. People are always told to be very careful because it’s straight to the hospital. And if he doesn’t like the sea as much as he likes lagoons, sometimes he ventures there. Patrick Valdivia, a fishing instructor and guide at Canet-en-Roussillon, fears this is causing “some anxiety among swimmers,” he says. “Maybe even this summer. »

However, the blue crab has an Achilles heel: its meat is edible and even, apparently, tasty. In some countries, particularly on the American Atlantic coast or in Spain and Tunisia, it is widely used for fishing. And Asia likes it. But not in France yet. However, experiments are ongoing as this may be a way to control this invasive species.

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