Economy before nature conservation: The European crayfish is on the brink of extinction – the crayfish plague and an invasive competitor deliberately introduced by humans have drastically decimated its populations. But how did this come about? A team of researchers has investigated why North American crayfish were brought to Europe in the 1960s and why crucial information about them was ignored at the time.
The whole story begins in the year 1860. In this year it is observed for the first time that European crayfish (Astacus astacus), also called noble crabs, die in large numbers. Responsible is a sham fungus that causes the cancer plague, which is fatal at least for European crabs. Around a hundred years later, in 1960, the disease had already depleted the populations of the noble crayfish considerably.
Fatal wrong decision
To compensate for the loss, the North American signal crab (Pacifastacus leniusculus) was released in rivers and lakes in Finland, Sweden, Austria and Spain. He seemed immune to the cancer plague. Today the signal crab has the upper hand in Europe’s waters, it has meanwhile been detected in 28 European countries. The European crayfish, on the other hand, is doing worse than ever and is now threatened with extinction.
The newly introduced signal crayfish is partly to blame for the decline of the native crayfish: “Although immigrants are resistant to most cancer plague strains, they can transmit the pathogen. When the animals were exposed en masse, the crayfish was given the death blow, as it were, ”says Kathrin Theissinger from the Senckenberg Biodiversity and Climate Research Center and the University of Koblenz-Landau. “What is explosive is that the signal crab did not get into European waters by accident, but was and is deliberately and repeatedly introduced despite scientific concerns”.
Commercial interests in the foreground
But how could such a wrong decision come about? Together with colleagues, Theissinger investigated what was behind the introduction of North American cancer. The first reason was purely economic, as the team found: Because crayfish are a sought-after food, the introduction of the signal crayfish was primarily about preserving this commercially profitable resource. The catch of the abandoned and soon developing wild populations of the signal crabs was supposed to compensate for the economic losses caused by the loss of the native crabs. Long-term ecological consequences of the release of an alien species were secondary to this.
In addition, false and distorted information about the North American crabs was conveyed. “It was not communicated that Pacifastacus leniusculus can transmit the cancer plague pathogen to native species, and it has repeatedly been claimed that signal crabs – in contrast to the native species – are immune to the cancer plague pathogen,” reports Theissinger. But that was not the case and so the introduced cancer became the multiplier of the cancer epidemic. This development could be fatal for many river ecosystems in Europe: “Not all river crayfish are the same. The ecological differences between alien species are often manifold and the effect on the ecosystem is difficult to predict, ”explains Theissinger.
The research team emphasizes that the European crayfish shows that it is more bad than good to introduce alien species to replace lost populations of native species. But what can be done to save the European crayfish after all? As the scientists explain, it would be important to ban the release, catch and sale of alien crabs as food in Europe. In addition, populations of alien crustaceans should be monitored and – as far as possible – new populations should be eradicated. A stronger education is also important: “We, society, have to perceive our environment more as a whole and value a functioning ecosystem. In order to avert the extinction of the European crayfish, one has to start with humans rather than crabs, ”says Theissinger.
Source: Senckenberg Research Institute and Nature Museums; Professional article: Frontiers in Ecology & Evolution, doi: 10.3389 / fevo.2021.648495