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An American crayfish in London (and beyond!)

Posted by on September 26, 2012

by Zara Gladman, PhD student at the University of Glasgow and intern at the Society of Biology

The North American signal crayfish

In my last blog I waxed lyrical on the wonders of crayfish, those large freshwater invertebrates that grace our rivers, lochs and your M&S sandwiches.  Today I’d like to discuss one of the biggest threats to aquatic biodiversity: the introduction of non-native crayfish to new ecosystems.

For the past four years, my life has been devoted to learning everything I can about one such invader, the North American signal crayfish (Pacifastacus leniusculus, pictured right).

Originally from western North America, this species was imported into Sweden for aquaculture in the 1950s and 60s.  Thereafter, introductions were made to several other countries including the UK.  Today, the signal crayfish is the most widespread non-native crayfish species in Europe.

Map of the signal crayfish invasion in Europe
(from Souty-Grosset et al. 2006)

This is not good news for our native plants and animals.  Signal crayfish are large, mobile “keystone species” with generalist diets.  This means that they have broad impacts on ecosystems, consuming anything from tiny invertebrates to fish.  They also compete with native crayfish (including the white-clawed crayfish) for food and space, and are vectors for the deadly “crayfish plague” disease, against which our native European crayfish have little or no resistance.

As well as affecting the living components of ecosystems, crayfish can modify the habitat structure by burrowing into the banks of rivers and lakes and accelerating erosion.

Damage to banking caused by crayfish burrows at Loch Ken

Damage to banking caused by crayfish burrows at Loch Ken, southern Scotland
(Photograph by Andrew Blunsum)

My PhD at the University of Glasgow focussed on the potential impact of signal crayfish in Scotland.  In particular, I was interested in how introduced crayfish might interact with native species of high conservation or economic value, including the freshwater pearl mussel (Margaritifera margaritifera) and Atlantic salmon (Salmo salar).

I also spent many a summer wading through rivers and streams, tracking the crayfish invasion.  Based on radio-tracking studies, we now know that signal crayfish are naturally invading our rivers at a rate of around 1 km a year. The deliberate, human-mediated introduction of signal crayfish to new locations remains a major concern.

The signal crayfish is not the first and will certainly not be the last non-native species to arrive in the UK.  A plethora of aliens including the Chinese mitten crab, killer shrimp, grey squirrel, American mink, carpet sea squirt and rhododendron are already established and causing significant environmental damage.  Climate change is also set to exacerbate the spread of certain species.  In the face of such challenges, raising the profile of invasive species through education and research is imperative.  As the old saying goes, “an ounce of prevention is worth a pound of cure”, and this should be our driving mantra in tackling this growing problem.

Chinese mitten crab
(photograph from the Natural History Museum)

Finally, to the signal crayfish, I say: “Kiss my Pacifastacus!”   For more information on invasive non-native species, you can visit the GB non-native species secretariat website here:

And if you’re a fan of videos, then here’s one I made about signal crayfish for the kids on “I’m a Scientist, Get me out of here!“:

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