Alien vs. Predator: Battle of the Non-Natives

Two non-native invasive species; the chinese mitten crab and the non-native crayfishs' ranges are set to overlap in the near future.

Both crustaceans are formidable predators, with a tendency to damage the ecology of their local environment. The signal crayfish Pacifastacus leniusculus, has so far caused the most widespread damage, in part because it is a vector for the plague disease that affects our native white-clawed crayfish Austropotamobius pallipes.

Speaking to the BBC, ecologist Stephanie Peay said: "Where the non-natives move in, the white-clawed crayfish [sic] are lost. Survey work has shown that it only takes between four and seven years from first arrival to achieve a complete local extinction. The only future for the white claws is in isolated water bodies that are completely free from non-native crayfish."

Both the mitten crab and the crayfish have a broad, generalist diet, the mitten crab being particularly unfussy when it comes to prey items, (plants, fish eggs and molluscs among these). The ecological niches of both species directly overlap, so it is likely there will be some kind of clash when the two species inevitably meet.

When either species is present in any British waterway, they will cause an overall loss in biological diversity and abundance of native species. One of the known mechanisms leading to invasiveness is enemy release. Because of the practicality of introducing natural enemies to curb these exotic beasts, this approach will remain unlikely. Conventional removal of these species by local authorities is currently probably the best method of dealing with these alien predators.

Defra's invasive non-native species framework strategy can be downloaded here.

The Environment Agency website lists some of the UK's worst offending non-native invasives.