In Spanish rivers and lakes we can find four species of crab. The American red crab ( Procambarus clarkii ), introduced from the marshes of Louisiana in 1973 on a farm in Extremadura, and the following year in the Guadalquivir, from where it spread to become an invasive species . That same year, introduced from Sweden, although also of American origin, the signal crab ( Pacifastacus leniusculus ), also invasive, entered. More recent is the introduction of the yabbie crab ( Cherax destructor ), Australian; it was introduced in 1983, it is also listed as an invasive species , although to a much lesser extent than previous species.
The fourth species is Austropotamobius pallipes , the white-legged crab , traditionally considered a native species . It is a very abundant animal in the recent past, but it has suffered serious impacts due to the introduction of the American species , which carry a lethal disease for it, called afanomycosis .
The mystery of the absence of the past
Although it is considered a native species, there is no paleontological, archaeological or historical evidence showing the presence of crayfish in the Iberian Peninsula. In fact, the Italian naturalist Ulisse Aldrovandi published in 1606 that the crayfish ” abounds in streams, rivers and lakes in Europe, but is not found in Spain, despite the fact that rivers are not scarce there “. And although he himself stated that he only spoke of animals “ that I have only seen with my own eyes ”, it seems strange that such an observant naturalist should not find an animal so apparently common .
It is Luis Cabrero de Córdoba, secretary of King Felipe II , who makes a first mention of crayfish in Spain, and he does so in the biography of the monarch. “ He even had fish brought from Flanders, carp, tench, burguetes and shrimp from Milan ”. In Italy, the crayfish is called “gambaro”, and this introduction corresponds to the one made in the El Escorial ponds as a gift from Francesco I de’ Medici to the Spanish king in 1588 . The first mention of the existence of crabs in the Iberian Peninsula is, in effect, the mention of their introduction. To find a reference to its wild state, it is necessary to wait until the year 1775, when the English naturalist William Bowles cites it in his Introduction to the natural history and physical geography of Spain .
What if it wasn’t native?
The hypothesis of the introduction is defended by the researcher Miguel Clavero , from the Doñana Biological Station (CSIC) . According to this approach, crabs were introduced in this transport of species in 1588 , as was done with many other species that later colonized the main Iberian basins from the El Escorial ponds . It is a hypothesis that explains the absence of records of crabs in the Iberian Peninsula both in the historical, archaeological and paleontological fields until the end of the 16th century.
A study led by Clavero in 2015 collected multidisciplinary information to test this hypothesis. They included not only historical information, but also taxonomic, genetic, ecological and even gastronomic information. The conclusions of the investigation pointed out that, in fact, the white-legged crab that we found so regularly before the invasion of the American crabs has, in fact, an Italian origin . In fact, at the genetic level, it has two peculiarities. On the one hand, the first analyzes carried out showed a low genetic diversity , something that fits with a pattern of introduction of few original specimens. And on the other hand, they have more similarities with the crab populations of the Milan region than with other populations geographically closer to Spain. Indeed, if these conclusions are true, the species would be Austropotamobius italicus , and not A. pallipes as hitherto considered.
But… what if it were native?
In reality, not all of the scientific community accepted the conclusions of Clavero’s team. Subsequent genetic analyzes showed a greater genetic diversity, which would correspond to what would be expected in a native species. In a scientific publication led by researcher María Díez-León , from the University of Guelph in Canada , in response to Clavero’s hypothesis, it is argued that in order to acquire such genetic variability, the population must have its origin at least 10,000 years ago .
However, there is an alternative hypothesis to this possibility, and it is that this genetic variability is due to the fact that the white-legged crab populations come not from a single introduction, but from several. And it is that, sometimes, the same data can give rise to very different conclusions, and in this case, completely contrary .
The scientific debate does not seem to be settled , and although the arguments put forward by Clavero’s group are very solid, even more conclusive evidence is needed in order to establish a scientific consensus.
And what does all this matter?
The white-legged crab in the Iberian Peninsula is in a critical state of conservation . Populations have been decimated to near extinction by aphanynomycosis, and many resources are devoted to their conservation and recovery. We are very clear that no resources should be devoted to the conservation of invasive crabs. If the white-legged crab turns out to be a native species, there is no doubt that those resources are well spent. However, if it wasn’t, would it make sense to preserve it? How long must an introduced species spend in a new ecosystem before it is assimilated as native, even if it is not?
In the long term, an introduced species is assumed as its own when it is functionally valuable in the ecosystem, or has been incorporated into cultural traditions. The walnut is a species native to the Middle East and introduced to the Iberian Peninsula by the Romans , but it is so well integrated into our ecosystems and our culture that investment in its conservation would not be denied if necessary. Would the same thing happen with the white-legged crab?
Whether or not the white-legged crab is indigenous is not only of biological importance, but also of cultural and social importance . It is possible that, given the high social value that the Spaniards attribute to this crab, the result of the scientific debate is indifferent, and whether or not it is native, efforts will continue to be devoted to its preservation.
After all, the ideal would be to try to recover habitats, and not just species . Just as we try to fix the messes caused by invasive species, when a non-native species is well integrated into the ecosystem, without causing impacts, there would be no reason not to conserve it .
