|Native wildlife species
|Invasive species risk
White-clawed crayfish (Austropotamobius pallipes)
UK locations: scattered locations across England and Wales
Population decline: Around 70% of the UK population has been lost since the 1970s
Vulnerability: Endangered worldwide
|The introduction of the American Signal crayfish (Pacifastacus leniusculus) to the UK by the fishing industry in the 1970s and 1980s, has decimated our only native crayfish. Signal crayfish aggressively out-compete for food and habitat and pass on crayfish plague, a lethal fungal infection for White-clawed crayfish. Their burrowing in riverbanks also harms the economy - affecting flooding, livestock safety and river-side structures – alongside predation on fish eggs reducing fish-stocks.
Red squirrel (Sciurus vulgaris)
UK locations: Extinct in large parts of England. Declining in Northern England, Scotland and Ireland.
Population decline: Reduced from an estimated 3.5million in the 19th century to 140,000 (a 96% loss)
Vulnerability: Endangered in Britain
|The decline of one of the nation’s most beloved species is a result of the introduction of an invasive species. The grey squirrel (Sciurus carolinensis) was introduced to the UK from North American by the Victorians, with escaped populations documented from 1876. Since then the red squirrel’s American cousin has been the main threat to its population, through transmitting squirrelpox and indirect competition for food and habitat.
Water vole (Arvicola amphibius)
UK locations: Across the UK but declining
Population decline: Disappeared from 94% of their former sites in Britain
Vulnerability: Endangered in Britain
|Best-known as the inspiration for ‘Ratty’ in Wind in the Willows, water voles have sharply declined in the UK. Predation by American mink (Neovison vison) is one of the main drivers of this loss. American mink first arrived in Britain in 1929 in commercial fur farms, with escaped and released mink reported as breeding wild from 1956. They are now present across most of the country and water voles form a key part of their prey.
Ash tree (Fraxinus excelsior)
UK locations: Nationwide
Population decline: Expected 80% decline
Vulnerability: Common but declining
|The non-native fungus Hymenoscyphus fraxineus caused the Ash dieback epidemic. It was confirmed in the UK in 2012 with contaminated imported saplings facilitating its spread. It is estimated to have a £15 billion economic cost this century – with half of this by 2030 – faced mostly by over-stretched Local Authorities.
Ash face additional invasive species threats with the Emerald Ash Borer beetle (Agrilus planipennis) progressing across Europe (though not yet found in the UK), which is highly fatal for ash populations
British freshwater shrimp (Gammarus pulex)
UK locations: Across Britain
Population decline: Unknown but declining
|Killer shrimp (Dikerogammarus villosus) were first discovered in the UK in 2010. They are considered one of the most damaging invasive species in the world. Not only do they eat other shrimp, invertebrates, fish eggs and small fish, they often kill other species but leave them uneaten, causing huge ecosystem damage.
Common earthworm (Lumbricus terrestris)
UK locations: Nationwide
Population decline: Under-recorded but declining
Vulnerability: Not monitored
|The New Zealand flatworm (Arthurdendyus triangulatus) was introduced to the UK through imported potted plants, soils and compost as early as the 1960s. This Invasive flatworm is already widespread and is a voracious predator which can reduce earthworm populations by 20% This earthworm loss impacts soil health, agricultural productivity and wildlife including birds.
Manx shearwater (Puffinus puffinus)
UK locations: UK offshore islands, such as Skomer (Wales) and Rum (Scotland).
Population decline: UK population may be up to 600,000 breeding pairs.
Vulnerability: Amber listed as a conservation priority
|The UK homes 80% of the world’s Manx Shearwater. But these globally important populations are threatened by the historical human-assisted introduction of brown and black rats (Rattus norvegicus & Rattus rattus) to their island homes. At least 13 colonies have gone extinct due to this invasive species. The population of this beloved bird is significantly rising after successful rat population control on several islands, but rat predation remains a big issue.
Juniper tree (Juniperus communis)
UK locations: patchy - mostly in Northern England and Scotland.
Population decline: Declining throughout the UK
Vulnerability: classed as Vulnerable and near-threatened
|One of the UK’s rarest trees, Juniper is threatened by the fungus-like pathogen Phytophthora austrocedri . This attacks the roots, and causes lesions into the lower stem, eventually cutting off the flow of nutrients entirely, killing the tree. This aggressive invasive species is thought to have arrived in Britain through the plant trade.
It is now found in over 100 sites – across the whole of the Juniper’s range in the UK. Loss of Juniper is impacting the Scottish Gin industry and affects specialised insects, lichens, and birds like the goldcrest.
Native flat oysters (Ostrea edulis)
UK locations: Distributed around Britain
Population decline: A critically low population as a result of overfishing in the 60s and invasives impacts.
Vulnerability: A species of national (GB) importance
|Both pacific oysters (Magallana gigas) and carpet sea squirt (Didemnum vexillum) threaten our native oysters. Pacific oysters were introduced to the UK in the 60s as it was thought our waters were too cold for them to breed. But warmer conditions from climate change are now facilitating population explosions throughout southern England and Wales, displacing native oysters. Carpet sea squirts are marine hitchhikers from the North West Pacific, which were first discovered in Great Britain in 2008. Colonies can smother species like our native oysters competing for a fix on a hard surface.
Depressed river mussel (Pseudanodonta complanata)
UK locations: Found in large running water habitats; large lowland rivers, large ditches and canals
UK Population decline: Distribution has declined by an estimated 30% in the last century
Vulnerability: Globally Vulnerable
|Native to the drainage basins of the Black, Caspian and Aral Seas, Zebra mussels (Dreissena polymorpha) have been in the UK since the 1800s. The Quagga mussel (Dreissena rostriformis bugensis) is originally from the Ukraine and was first found in the UK in Egham, Surrey, in October 2014. They both form massive populations covering the beds of water courses and water bodies, attaching to the shells of, and smothering, native mussel beds. They also have an economic impact, clogging water intake pipes and filter screens and causing damage to boat hulls.
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