The tasty (and troublesome) American crab biology The tasty (and troublesome) American crab

The American crayfish , Procambarus clarkii , is a decapod crustacean that inhabits freshwater courses and is native to the coast of the Gulf of Mexico. It has been introduced for different reasons in countries in Asia, Europe and Africa. While in northern Europe the populations maintain a controlled growth and do not pose a big problem, in the southern countries of the continent, including Spain, this species has become a veritable pest.

Morphology of an invasive crustacean

Adult individuals can reach 12cm in length and 50g in weight. It is distinguished from other species by its characteristic red color (its other common name is precisely “red crab”), particularly by the presence of bright red bumps on its claws . These have a considerable size despite the small size of the crabs, being almost as long as the body of the animal.

The tasty
The tasty

It is a species resistant to droughts , being even capable of moving several kilometers in dry terrain. It is also tolerant of salt water, which is rare among freshwater crabs. This resistance to environmental changes allows it to colonize waterways quickly, taking advantage of the fact that it can survive in conditions that other species of crabs do not tolerate.

In the US, as well as in countries where the species was introduced for captive breeding, the red crab is a fairly popular food . So much so that in the 90s this species of freshwater crab was the most consumed worldwide, with 90% of the world market corresponding to specimens from Louisiana. It was this popularity that led to it being exported to other countries and subsequently becoming a serious problem for ecosystems.

American crab problem

As in other similar cases of biological invasions, the problem came when individuals of American crabs were released to the natural environment and there they established wild populations, which began to expand rapidly. In the case of Spain, the main problem is that this species competes with native species of freshwater crabs, displacing them from their habitats.

The two native species that are threatened by the American crab in Spain are Austropotamobius pallipes , the “white-legged crab”, and the Astacus astacus , also called “noble crab”. Both species are found throughout much of Europe, but it is also the case of the American crab. The white-legged crab is on the IUCN list of threatened species.

The main problem with the American crayfish, however, is that it is a carrier species for the parasite Aphanomyces astaci , which does not affect the crayfish but does affect the native European species. This parasite causes a disease called aphanomycosis or crab plague, with a mortality of 100% and that decimates entire populations in the rivers where it occurs. 

The measures proposed to combat this disease are to avoid the introduction of American crab in those waterways where it is not present (something that has already been prohibited, as will be explained later) and to clean the fishing gear used in river areas. where the parasite has already been detected. In addition, the construction of containment dikes in watercourses to prevent crabs from going upstream has been shown to be effective in containing the disease in the lower reaches of rivers.

There is another freshwater crab native to the US that has been introduced to Europe, Pacifastacus leniusculus . This species comes from the Atlantic coast, unlike the red crab, and its common name is “Pacific crab” or “signal crab”. It is not commercially used and therefore is less widespread than the red crab, but the Pacific crab is also a predator that competes with the native species of Spain and is also a carrier of aphanomycosis

Controversy in the classification of the American crab as an invasive species

Due to the great voracity of the American crab (which feeds on a greater variety of prey than native crabs), because it displaces the autochthonous species and because it is a carrier of several diseases (not only aphanomycosis), the species has been included in the Spanish catalog of invasive alien species . This means that the commercial use of the species is prohibited throughout the Spanish territory, including the transport of specimens and their capture.

This measure, although justified, has generated some controversy on the part of the fishermen’s collective and those companies that were dedicated to the commercial breeding of the American crab . The red crab nurseries in the Guadalquivir marshes had the highest European production (and second worldwide) of this species. The profits generated by red crab farming exceeded 20 million euros per year.

The companies affected by the ban have appealed to the Constitutional Court the ruling of the Supreme Court that included the species in the Spanish catalog of invasive alien species (after a moratorium on this measure by the Government, just as it happened in the case of the rui or of the black bass, perch American).

Leaving aside the fact that it was these same companies that introduced the American crab to Spain and therefore those responsible, albeit indirectly, for the serious damage it causes to native species (along with fishermen), appeal the judgment of the Supreme Court makes little sense. For two reasons:

  • First, because a judgment of the Supreme Court is final.
  • Second, because an invasive species will remain invasive no matter how desirable it is for fishermen to fish (precisely because it grows faster than native species, like black bass) or because it is lucrative to raise it for commercial purposes.

The priority when it comes to legislating and caring for the environment should not be leisure or economic benefits, but rather to conserve our natural wealth in the long term.

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