Self-replicating crayfish threaten the ecosystem of a historic Austro-Hungarian lake
Lake Fertő has long struggled with invasive species, but the arrival of the marbled crayfish takes the problem to a new level. This crustacean reproduces without males, meaning a single individual can give rise to an entire colony.
Experts fear the lake’s fragile ecosystem will not be able to cope with such an intruder – especially as the species can also spread a deadly disease.
From German aquariums to open waters
The marbled crayfish first appeared in the 1990s among German aquarists. It originated from the American crayfish, one of whose lineages suddenly developed a new mode of reproduction. This is what makes the animal particularly dangerous.
The marbled crayfish reproduces through parthenogenesis: every individual is female and capable of producing offspring on its own. In practice, this means that even a single specimen is enough to establish a population within a short time.
Initially, the species was kept in aquariums, but because of its rapid reproduction many owners released them into nearby waters. From there, the crayfish spread across Europe and has since been recorded on other continents, with known populations in Africa and Asia as well.
In Hungary, it was first detected in artificial habitats such as thermal lakes and urban canals. Researchers now warn, however, that the real danger has only just begun.
Crayfish plague can wipe out entire populations
The animal itself is already a serious problem, but the greatest threat comes from a disease it carries: crayfish plague. This fungal pathogen is almost always fatal for Europe’s native crayfish species, which lack any natural resistance. Once it appears, it can destroy entire populations within weeks – and there is virtually no way to stop it.
The risk is compounded by the fact that the native European crayfish, once common in Hungarian waters, has already been in decline. If crayfish plague gains a foothold around Lake Fertő, the remaining populations could disappear for good.
Hungarian researchers confirmed its presence
Austrian scientists already reported a mass outbreak of the species on the western shores of Lake Fertő in the summer of 2023. This spring, Hungarian researchers also confirmed its presence: experts from the Fertő–Hanság National Park and the Hungarian Ichthyological Society captured several specimens near Fertőrákos and Virágosmajor harbour. According to magyarallatvedelem.hu, they used both hand nets and electrofishing equipment to confirm the species’ presence.
The marbled crayfish causes problems on several fronts. It competes with native species for food, undermines shorelines, and damages drainage systems.
During sampling, other invasive fish species – such as pumpkinseed and round goby – were also detected, showing that Lake Fertő is increasingly becoming a haven for uninvited guests.
According to the researchers, the recent captures themselves already count as a warning sign. If the species spreads further, the ecological balance and native wildlife of Lake Fertő could be in jeopardy. Preventive measures, they stress, are needed as soon as possible – before it becomes impossible to contain the species.