Posted on: 22 August, 2023
This World Water Week (20-24 August) we’re shining a light on our conservation work with one of the UK’s most endangered species, the white-clawed crayfish. Under threat from the invasive North American signal crayfish, Bristol Zoological Society has been working to protect white-clawed crayfish since 2008.
But as a small and seemingly insignificant invertebrate, why do we care about the protection of the white-clawed crayfish, and why is the signal crayfish a problem?
An invasive species is an animal or plant that is not native to a particular area, and harms that environment after being introduced to it by humans.
The North American signal crayfish carries crayfish plague — a deadly disease to which they are immune, but that kills our native white-clawed crayfish. They are also larger than the white-clawed, outcompeting them for food and habitat, as well as sometimes predating them.
Yes! Our native crayfish works in harmony with, and benefits our aquatic ecosystems, whereas the invasive species causes them harm.
White-clawed crayfish are considered ‘ecosystem engineers’— species that modify, maintain or create habitat. Crayfish are maintenance engineers, playing a significant part in keeping waterways clean. They forage on the bottom of streams for invertebrates, carrion, water plants and dead organic matter— helping to keep streams clean and healthy for all the species that rely on them.
In contrast, signal crayfish harm the ecosystem by burrowing extensively into river banks, weakening bank stability which can lead to collapse, increasing the risk of flooding in some areas. They also predate many other native species that the white-clawed does not, such as coarse fish and their eggs, altering fish populations and harming established food webs.
As well as keeping streams clean and healthy, white-clawed crayfish are an important food source for some of the charismatic species we associate with our waterways. Otters, herons and even dragonfly larvae rely on white-clawed crayfish as an important food source.
You might not expect it of this little invertebrate, but our native crayfish have a social structure within their communities. They form dominance hierarchies where the strongest, largest crayfish claim the best refuges!
Female white-clawed crayfish hold their eggs outside their bodies (under their tails) for 8-9 months as the eggs develop. After the eggs have hatched, the hatchlings remain attached to their mother for the first two weeks of their life. When they detach, the young crayfish have to swim sideways as their movement is restricted until their second moult, when they become little versions of the adult crayfish.
White-clawed crayfish can live up to 10 years! They’re slow growing and like other crustaceans such as lobsters and crabs, have to go through many moults before they reach sexual maturity, at about 2 years. This slow maturing means there’s a high risk of predation before they reach breeding age. Every crayfish matters!
Stop the spread of invasive plants and animals from one water body to another by ensuring you check, clean and dry all equipment, shoes and clothing that have been around waterways.