Alien Invasion of the Crustacean Kind

When aliens invaded earth in ‘War of the Worlds’ it was a disease which saved the human race. When aliens invaded earth in ‘Independence Day’ Will Smith saved the world with a computer virus. When the signal crayfish invaded our European waters we had no disease or virus to save our biodiversity. Instead, this devious critter came prepared, bringing with it a disease of its own: the crayfish plague.

The crayfish plague, Aphanomyces astaci, is a fungal disease which was brought to Europe with the introduction of the signal crayfish into our aquaculture industry. The fungal disease can kill native white-clawed crayfish within a matter of weeks following infection.  Yet the signal crayfish, having co-evolved with the fungal pathogen for centuries, is resistant.

Bio-warfare isn’t the only way the signal crayfish threatens its native cousin. The invader grows larger than the white-clawed crayfish and often wins in the competitive battle for resources such as food and refuge. If that wasn’t enough, a study in Finland has demonstrated that male signal crayfish can significantly reduce populations of white-clawed crayfish through reproductive interference. The larger, dominant signal males exclude the smaller native males, resulting in the majority of eggs produced by the native white-clawed crayfish females being sterile.

The spread of signal crayfish throughoutEuropeis a major cause for concern with human-mediated activities playing a large role as a vector of dispersal. These crayfish in early life stages, and the associated crayfish plague, can be easily transported between water bodies through recreational activities such as fishing and boating. A call for improved biosecurity has been issued in many countries, including the ‘Check, Clean, Dry’ campaign in the UK which is designed to limit the spread of invasive aquatic species such as the killer shrimp and the signal crayfish.

You can help RINSE keep track of this alien invader by reporting your sightings using our free Smartphone app ‘That’s Invasive!’

To identify this crayfish look out for:

• Reddish brown coloured body
• Bright red underside of claws
• A white spot on the upper side at the claw hinge

References

Bubb, D. H., Thom, T. J & Lucas, M. C (2005). ‘The within-catchment invasion of the non-indigenous signal crayfish Pacifasticus leniusculus

 (Dana) in upland rivers. 376-377

Dunn, J. C., McClymont, E., Christmas, M & Dunn, A. M (2009). ‘Competition and parasitism in the native white clawed crayfish and the invasive signal crayfish in theUK’ Biological Invasions 11: 315-324

Independence Day – The Movie.

Photo Credits: Independance Day Alien (Alistair McMillian), Signal Crayfish (Matt Brazier - Environment Agency) and Signal Crayfish (GBNNSS)