Yankee ‘invaders’ threaten UK’s crayfish

U. LEEDS (UK) — Better resistance to parasites and a less fussy diet are allowing aggressive signal crayfish from the US to threaten white-clawed crayfish native to Yorkshire.

The Yorkshire crayfish suffers from two parasites: plague, which is carried by the American invader, and porcelain disease that makes it sluggish and suppresses its appetite before eventually killing it a few years later.

Yorkshire is one of the last strongholds of the white-clawed crayfish, which is being driven out of Britain’s waterways by its hardier American cousin, introduced to Britain in the 1970s for fish farming.


The advance of the signal crayfish over its native rival has implications for the biodiversity of Britain’s rivers as the diversity of prey is reduced and the invaders’ appetite for fish eggs causes a decline in the fish population.

Although the white-clawed crayfish is listed as an endangered species in Britain, the reasons for its decline and the American species’ success have not been well understood.

Now, researchers from the University of Leeds’ Faculty of Biological Sciences have been trying to work out why the signal crayfish has been gaining the upper hand, and how this information might be used in conservation projects.

Published  online in the journal PLoS One, the study compares how quickly the two different species deal with food.  The American signal crayfish eat up to 83 percent more food per day than do their native cousins.

The research also shows that white-clawed crayfish are much more choosy about what they eat, preferring particular types of prey, while the signals eat equal amounts of all prey.

The white-clawed crayfish are also affected by a common parasite, porcelain disease, which affects their ability to catch prey, leading affected crayfish to eat 30 percent less. The American signal crayfish, on the other hand, seem unaffected by the parasite.

“The signals eat much more compared with the native crayfish,” says Alison Dunn, of the faculty of biological sciences, who led the study. “But the situation is exacerbated by a parasite which essentially changes the native’s behavior—the white-clawed crayfish can’t eat or handle as much food as the signal, because the parasite weakens its muscles.

“The huge appetites of the signal crayfish can have a massive effect on the whole ecosystem,” she says. “In particular it affects biodiversity because there is a reduction in the numbers of prey. In some Yorkshire rivers, for example, the fish population has declined because signal crayfish are eating large numbers of fish eggs.”

Dunn believes studying the effects of parasites on host species can offer vital clues about species conservation.

“Parasites are a fascinating and vital part of any ecosystem and you have to consider their effects when looking at biological invasions,” she says. “We hope our findings will help us make predictions about how this invader might spread and help with management strategies.”

Humans too can play a part in protecting the white-clawed crayfish by understanding how invading species spread. The signal crayfish is able to move overland of its own accord, but may also be inadvertently moved around in, for example, damp fishing gear, Dunn explains.

“We need to be much more careful about how we move animals and plants around from habitat to habitat, and raise public awareness about these issues.”

The research was funded by the Natural Environment Research Council, in partnership with the Environment Agency.

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