The Antwerp city cemetery Schoonselhof has been invaded by hundreds of marbled crayfish in pools and streams around the grounds, presenting a danger to local biodiversity, according to the Flemish Institute for Nature and Woodland Research (INBO).
The marbled crayfish (Procambarus virginalis) is a creature that does not exist in nature, but is thought to have been created experimentally by pet traders in Germany in the 1990s.
The crayfish is similar to the slough crayfish found in Florida in the US, with one important difference: it is parthenogenetic, which means it is able to reproduce without mating, and all offspring are female and genetically identical.
That characteristic makes it easy for a large population to spring up quickly, which is what appears to have happened in Antwerp.
“Someone apparently had the animal in their aquarium, and then set it free in a canal,” said Kevin Scheers of the INBO. “It’s impossible to round up all of them. It’s like trying to empty the ocean with a thimble.”
Marbled crayfish have already been spotted in the Berchem area of Antwerp, as well as two sightings near Leuven.
“Often people get tired of their animals or the marbled crayfish population is getting too large at home,” said Scheers. “It must seem like a good idea to let the animals loose in nature.”
Since a single example can clone itself and so reproduce exponentially, it represents a threat to the local environment. The crayfish eats anything it can get hold of, and is able to travel up to 2km and dig down to a depth of one metre.
“The marbled crayfish is about 10cm in size and crawls around both in the water and over land at night,” Scheers said. “That’s how they move to other canals and pools.”
For the time being, there is no easy way of getting rid of the growing population.
“In Spain they tried some experiments with poison, but that is not permitted in Belgium.”
In 2014 the European Union introduced a total ban on “the possession, trade, transport, production and release” of the species in the wild. However since all examples of the species are identical, it would be impossible to trace back to wherever the cemetery examples came from.
The Brussels Times