The American Signal Crayfish Invasion - Planet Earth Online

Chris -   Native white-clawed British crayfish are in trouble.  Weakened by a parasite, this endangered species is being driven out of waterways by the North American signal crayfish.  Planet Earth Podcast Presenter, Richard Hollingham, headed to Yorkshire to meet Alison Dunn and Neal Haddaway from the University of Leeds and, first, Martin Christmas from the Environment Agency.  As they stood beside a stream (or as it's Yorkshire - a beck), Richard asked Martin what damage the American imposter was doing...

Martin Christmas - Signal crayfish because they're bigger, they're more aggressive.  They tend to out compete for the same habitats, so white clawed crayfish get pushed out. Signal crayfish also bring with them the crayfish plague which they can carry but aren't so susceptible to, but native crayfish really do suffer from plague outbreaks, it wipe them out. So, those are two of the conservation issues we've got.  Also, from the Environment Agency's perspective, signal crayfish are really good diggers, particularly in soft banks, and they can cause expensive problems in terms of undermining banks, bank collapses and maintaining flood banks is something that we invest a lot of money in every year.

Richard Hollingham -   There are two things going on here, Alison, the fact that these signal crayfish are causing damage but also they are carrying this disease which affects the native crayfish.

Alison Dunn -   There are two different diseases that are important for who wins that competitive interaction.  There's the plague that Martin referred to, which the signal crayfish have brought to this country and it kills the white clawed.  The other thing that's fascinating that we're looking at is a parasite called porcelain disease that changes how the native crayfish is able to feed.  It affects its behaviour and its ability to catch its prey and as a knock on effect its ability to compete with the invader.

Richard Hollingham -   It sounds a bit like the red squirrel, the native red squirrel and the grey squirrel, the American invader.

Alison Dunn -   It is - it's a very similar situation. The plague is analogous to the squirrel pox virus, but the effect that we're looking at, the parasite that we're looking at - porcelain disease - is actually a native parasite and it only seems to affect the behaviour of the native crayfish.  It makes it more sluggish, less able to catch its prey which Neil will tell us about.

Richard Hollingham -   So, what does your research involve? What were you looking at?

Neil Haddaway -   This particular research that we did was some lab based studies looking at the amount of food that the crayfish were eating.  In particular we were interested in comparing the amount of food that the invasive crayfish ate, the amount of food the native crayfish ate and looking at the effect of the disease on the native.  And what we found was that the invasive crayfish ate about 83% more food, but not only that it showed very little choice in what it was eating. The native crayfish with the disease ate, on average, 30% less and it also ate slower, so it was changing the way that it was eating.  But not only this it was also changing it's choice of prey, so instead of going for fast moving prey the diseased crayfish were preferring animals that walked along the bottom as they were easier to catch.

Richard Hollingham -   So really, the native crayfish was losing out food wise on all counts?

Neil Haddaway -   Definitely, the native crayfish can't really compete when it comes to eating food with the invasive and the disease really did knock it for six.

Richard Hollingham -   So how do you use research like this, Alison?

Alison Dunn -   Understanding the processes going on in an ecosystem and understanding how important disease can be in modifying interactions, whether it's between an animal and its prey or between an animal and another one with which it competes are important to understanding how ecosystems are made up.  And biological invasions are enormously important economically and in terms of biodiversity across the whole globe. In terms of losing our diversity of animals and plants they are second only after habit destruction as being a cause of loss of species across the globe.  So by understanding in this small beck how disease modifies the interaction between the native and invasive we could develop our understanding at a much broader level of invasive species and the importance of disease.

Richard Hollingham -   So coming back to the white clawed British crayfish, does that mean you can save it?

Alison Dunn -   The white clawed crayfish will continue to decline both as a result of interactions with the signal and with the disease but I think the Environment Agency have strategies to try and slow the spread of the signal crayfish and to develop isolated populations where we can conserve our native species.

Richard Hollingham -   So all is not lost?

Alison Dunn -   No, all is not lost.