What are invasive species?

What are aquatic invasive species?

 The Signal Crayfish on the right above is an invasive species, not to be confused with our native Crayfish on the left of the picture above                                                                                                                                                                                           

Animals and plants that have been introduced by human actions to parts of the world outside their natural range are known as non-native species. Most of these animals and plants do not cause any problems in Great Britain.

However, a few species can cause serious and permanent problems by harming ecosystems. They can be bigger, faster growing or more aggressive than native species, and may also have fewer natural predators to control their numbers. As a result, native species are often unable to compete and the non-native species are able to take over. These species are called invasive non-native species. Aquatic invasive species are non-native plants and animals that have been introduced into GB waters.

Why should we be concerned about aquatic invasive species?

These species can devastate populations of native species and change whole ecosystems for example by competing with and displacing native species, spreading disease, altering the local ecology and physically clogging waterways.

This can adversely affect recreational facilities, for example, by reducing the population of fish, restricting navigation through waterways and affecting the quality of our rivers.

What are the economic implications of the problem?

The cost of managing aquatic invasive species runs into millions of pounds. A report published in November 2010 by CABI: “The Economic Costs of Invasive Non-native 2

Species on Great Britain” estimates that the cost to the GB economy of all invasive non-native species, including aquatic species, is at least £1.7billion per annum. For a full copy of this report please click on the top link on this web page.

Examples of the costs of managing invasive aquatic species:

American signal crayfish is estimated to be costing GB over £2.6m per year in terms of management to protect the native white-clawed crayfish; river bank restoration; angling impacts and research.

Floating pennywort is estimated to be costing GB over £25m per year in terms of control and costs to leisure and recreation such as angling and boating.

How are aquatic invasive species usually spread?

Water users can unknowingly assist the spread of these species from one water body to another by accidently carrying individuals, eggs, larvae and viable plant fragments on their equipment, shoes, clothing and other damp places. For example, new research from the Environment Agency has shown that a killer shrimp can survive in the moist fold of a wader for up to 15 days.

What are some of the worst aquatic invasive species?

Five of the worst aquatic invasive species include ‘Killer Shrimp’ (Dikerogammarus villosus); Floating Pennywort (Hydrocotyle ranunculoides); Water Primrose (Ludwigia peploides); Zebra Mussel (Dreissena polymorpha) and Quagga Mussel (Dreissena rostriformis).

What can we do to stop the spread of aquatic invasive species?

By following three simple steps when leaving the water, we can help stop the spread of aquatic invasive species.


 Check your equipment and clothing for live organisms - particularly in areas that are damp or hard to inspect



 Clean and wash all equipment, footwear and clothing thoroughly.

 If you do come across any organisms, leave them at the water body where you found them.



 Dry all equipment and clothing – some species can live for many days in moist conditions.

 Make sure you don’t transfer water elsewhere.