Research led by the Centre for Ecology and Hydrology (CEH) has revealed the alien plant and animal species which are not yet established in the EU but could threaten European biodiversity.
43 scientists across Europe worked together to analyse 329 alien species and the level of threat they pose. They agreed that eight are considered to be very high risk, 40 are high risk and 18 are medium risk.
“Preventing the arrival of invasive alien species is the most effective way of managing invasions,” says Professor Helen Roy at CEH, who led the research.
“Predicting which species are likely to arrive and survive in new regions involves considering many interacting ecological and socio-economic factors including climate but also patterns of trade.”
There are currently more than 14,000 alien species in Europe, more than half of which originated outside EU territories and the remaining have originated in some EU countries and subsequently invaded others.
Some alien species are considered to be relatively benign in their new country, including the tree bumblebee in the UK, whereas some can cause harm or affect native species and are labelled as invasive species, including the signal crayfish.
"We know the sorts of impacts invasive alien species can cause," says Professor Juliet Brodie from the Natural History Museum, who was involved in the research.
"The green seaweed Codium parvulum, for example, has been reported to produce massive drifts c. 10 km long by 3 km wide and 20 cm thick, weighing an approximate 6000 tons."
The research shows that terrestrial invertebrates are most likely to arrive with goods such as plants, whereas aquatic species usually arrive via ships.
The eight species with the highest risk are:
Northern snakehead Channa argus
A fish species which is native to southern and eastern China. It is now widely distributed in Japan's shallow, marshy ponds and wetlands, where it preys on native fish species.
Rusty crayfish Orconectes rusticus
The large and aggressive freshwater crayfish species is native to the USA, but is now also found in Canada where is it more successful in deterring attack from predators than other crayfish, and is now outcompeting native species.
Striped eel catfish Plotosus lineatus
This venomous catfish species is native to the Indian Ocean, however it was recorded in the Mediterranean in 2002 and has spread rapidly along the Israeli coast. Inhabiting sandy and muddy substrates, it competes and displaces other species.
Codium green seaweed Codium parvulum
This seaweed species is considered to an ecosystem engineer as it alters the structure and functionality of ecosystems. It is native to the Indo-Pacific Ocean, but has also been found in the Red Sea, off the northern shores of Israel and the Lebanese coast.
Onyx slipper snail Crepidula onyx
A native to the southern coast of California and northern Pacific coast of Mexico, the onyx slipper snail is now widespread. It is highly invasive in Korea, Japan and Hong Kong.
Black striped mussel Mytilopsis sallei
The black striped mussel lives in brackish areas along the Pacific coast of Panama. However, it invaded the Indo-Pacific Ocean during the 1990s and has been found in Australia, Fiji, India, Japan, Malaysia and Taiwan. It can completely dominate some coastal areas as it is able to survive extreme environmental conditions.
Fox squirrel Sciurus niger
Native to eastern and central North America, the fox squirrel competes for resources with the western grey and Douglas squirrels.
