Top 10 Facts: Surprising UK Non-Natives

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American Bullfrog Lithobates catesbeianus. Around twice the length of our native Common Frog, American Bullfrogs are most often identified by their loud, deep calls. Deemed a risk to British wildlife due to their tendency to prey on everything from small mammals and ducklings to other amphibians, Bullfrogs may also spread Batrachochytrium dendrobatidis – a form of Chytrid fungus – to native amphibians. Due to their negative impact on the native ecosystems, bullfrogs have been subject to an eradication scheme, costing up to £100,000 to date. Despite conservationist’s best efforts, this species remains present in a select few areas across England. Did you know that bullfrog tadpoles can grow up to 15cm?

Topmouth Gudgeon Pseudorasbora parva. Widespread but scattered across England, Topmouth Gudgeon inhabit well-vegetated ponds, channels and lakes. This nondescript fish species compete with native fish and farmed stock for food, and has been found to severely deplete or even eradicate native fish and invertebrate populations in areas of particularly high density – gudgeon have been recorded at densities of up to 60 fish per square meter – and has been directly linked to the eutrophication of British waterbodies due to it’s feeding tendencies which limit zooplankton abundance. Thus, in turn, increasing phytoplankton prevalence.

Coati Nasua nasua. A close relative of the North American Raccoon, up to ten animals were known to be living wild in South Cumbria until at least 2008. Given the small-scale of the reported population there are no known environmental impacts at present; though it is thought that, should this population expand or future escapes occur, that the Coati could become a significant predator of native wildlife. South Lakes Wild Animal Park was initially implicated in the spread of Coati’s in Cumbria, although the spread of sightings – ranging from Kendal and Kentmere to Langdale and Penrith – suggest other possible escapes.

American Skunk-cabbage Lysichiton americanus. A rather conspicuous plant boasting yellow flowers aesthetically similar to native Lords and Ladies, the stronghold of Skunk-cabbage appears to be Southeast England, most notably Hampshire. Although populations now exist at various intervals between Cornwall and Inverness. Like many invasive botanicals, this species is thought to decrease floral diversity within occupied areas and it is thought – based on Germans studies – that it can have a significant impact upon marshland plant communities. The economic impact of American Skunk-cabbage remains unknown; though with the species seemingly consolidating its hold in the UK, it is likely that further study will be needed to properly assess its impact.


American Skunk-cabbage

Quagga Mussel Dreissena bugensis. In October 2014 Quagga Mussel was found in Wraysbury Reservoir and the Wraysbury River, near Egham, Surrey –  the first UK record of this decorative yet damaging species. Originally from the Ponto-Caspian region, the mussel can significantly alter whole ecosystems by filtering out large quantities of nutrients and is also a thought to pose a serious biofouling risk by blocking pipes and smothering boat hulls. It is thought that there are no effective eradication techniques for Quagga Mussel once it becomes established, thus all records of this species should be reported immediately.

Carolina Wood Duck Aix sponsa. The wood duck is the only congener of mandarin duck and females and young birds are hard to distinguish from that species – meaning that this species may go unrecorded in many instances. First reported in the wild during the 1830’s Wood Ducks have been recorded breeding at many locations across the UK including in Wiltshire, Berkshire, Devon and Kent. Despite this, the species has not yet formed a self-sustaining population anywhere in the UK. While there is potential for Wood Ducks to compete for nest-sites with other hole-nesting bird species, this is one non-native species that does not appear to have an overwhelmingly negative impact on the British ecosystem. With escapes from captivity still relatively common, it is likely that individuals will continue to be found wild long into the future.


Carolina Wood Duck

Pitcher Plant. There are currently twelve known populations of this carnivorous plant species known from the UK, with the largest being found on Wedholme Flow where there are ongoing efforts to control numbers. The species has been eradicated from a further ten sites across the UK; where the vector for introduction was thought to be transplanting from private collections. Large Pitcher Plant populations have been shown to restrict the growth of native botanicals and, based on studies in Ireland, it is thought that the species may impact upon peat regeneration due to its tendency to restrict the growth of Sphagnum Moss. There are no known economic effects of this species, with the cost of removal covered, to date, by conservation bodies in charge of the reserves on which it grows.

Wels Catfish Silurus glanis. Growing up to 3m in length across its native range in Europe and Asia, this catfish is a voracious predator of birds, mammals, amphibians and invertebrates and. as such, there is concern that the presence of this species within UK waters may have an adverse effect on biodiversity. Indeed, studies from Spain suggest that the Wels may have a detrimental impact on waterbird populations. Widespread but scarce in the UK, the majority of Wels sightings come from Southern England where, despite expert advise, it is continuously stocked for sporting purposes. The first official record of this species living wild in the UK was at Morton Hall, Norfolk during 1864.


Wels Catfish

Tree-Of-Heaven Ailanthus altissima. With elongated, pinnate leaves, this species appears not dissimilar to Walnut or Ash and is planted heavily in urban areas. This has led to its escape in Southern England – occurring to such an extent that it has now become invasive in the London area. The impact of Tree-Of-Heaven remains relatively small due to its presence in areas of low conservation value; though it is thought that as temperatures warm, the species will acclimatise more readily to the natural ecosystem. In areas of Southern Europe – where the species has already established – Tree-Of-Heaven has been shown to actively exclude native flora. The plant also poses a slight risk to humans with the mild toxins found within the leaves often causing dermatitis upon contact.

Killer Algae Caulerpa taxifolia. A bright green seaweed with upright leafy fronds, dense growths of this marine plant can significantly alter habitat structure by displacing both floral and faunal species. It is also inedible to most native species, has been shown to smother sea-grass meadows – an important habitat type for many native marine species – and causes myriad problems for humans by reducing fish stocks and impacting upon the performance of fishing gear. Very popular in the marine aquarium trade in the UK, this species is not known to exist in the wild just yet; though based on it’s severe impact upon the Mediterranian ecosystem, it deserves a spot on this list nonetheless. Indeed, conservationists and anglers alike are predicting its spread into the wild in the very near future. Perhaps this addition to the list can be seen as a forewarning of things to come?