BBC News

'Killer' shrimps worst alien invader of waterways

image captionDikerogammarus villosus shrimp have a voracious appetite which can alter the habitats it invades

'Killer' shrimp is the worst non-native invader of England and Wales' waterways, says the Environment Agency.

Known as Dikerogammarus villosus, it kills native shrimp and young fish.

The Environment Agency's worst 10 alien invaders include water primrose, giant hogweed and Japanese knotweed which can damage riverbanks and buildings.

The agency said invasive species cost the UK about £1.7bn a year and it will work with partner groups to manage the spread of damaging plants and animals.

Several species of pond plant which have escaped from gardens and parks are also on the list of non-native wildlife which pose the greatest threat to the country's rivers and lakes.

Increased damage to riverbanks and buildings can increase the risk of floods and hit native wildlife.

Tough EU targets

Invasive species can even become so prolific that anglers, fishermen and boaters cannot use the waterways.

Despite growing to just 30mm long, Dikerogammarus villosus has been identified as being the worst alien invader due to its voracious appetite which alters the make-up of habitats it invades.

Other creatures in the Environment Agency's most wanted list include the American signal crayfish which has endangered our native white-clawed species, the topmouth gudgeon fish which hits other species, and the mink, which eats water voles.

Water primrose, the floating pennywort and parrot's feather are pond plants which have caused problems after spreading into the environment, clogging up and damaging water habitats.

Giant hogweed, Japanese knotweed and Himalayan balsam are all taking their toll on riverbanks and other areas across the UK.

The hogweed contains a poisonous sap, the knotweed causes structural damage and all three suppress native plants and cause soil erosion.

The Environment Agency warned that the invasive species could hamper efforts to improve the quality of rivers to meet tough new EU targets.

It said it is already spending £2m a year controlling invasive species, and will be increasing its efforts with partners such as government conservation agency Natural England.

Trevor Renals, invasive species expert at the Environment Agency, said if invasive species are not controlled there is a risk of losing some native species and incurring even more clean-up costs, as well as "falling short of the strict EU targets for our rivers and lakes".

He said: "The Environment Agency will be working with other environment bodies as well as community and volunteer groups to manage the spread of these damaging plants and animals.

"We would urge everyone to help stop the spread of these species by making sure that garden and pond plants don't end up near rivers and parkland and thoroughly cleaning any fishing, boating and canoeing equipment when moving between waterways."