Scientists have identified 66 alien plant and animal species that are not yet established in the EU region, but if introduced would be most likely to pose a threat to biodiversity and ecosystems.

From an initial working list of 329 alien species considered to pose threats to biodiversity recently published by the EU, scientists have derived and agreed a list of eight species considered to be very high risk, 50 considered to be high risk, and 18 considered to be medium risk.
The research, with substantial contribution of Sven Bacher of the University of Fribourg and involving 43 people from across Europe and funded by the European Commission, is due to be published on 6 December in the journal Global Change Biology.
The authors developed a horizon scanning approach in order to derive a ranked list of potential invasive alien species (IAS). Using this procedure, they worked collaboratively to reach consensus about the alien species most likely to arrive, establish, spread and have an impact on biodiversity in the region over the next decade.

The approach is unique in the continental scale examined, the breadth of taxonomic groups and environments considered, and the methods and data sources used.  Species considered included plants, terrestrial invertebrates, marine species, freshwater invertebrates and vertebrates.

The eight species that pose the highest risk are:

• Channa argus – northern snakehead, a fish species native to southern and eastern China but introduced to Japan in early 1900s. It is distributed widely in Japan within shallow, marshy ponds and wetlands where it preys on native fish species. Most likely pathway is the introduction of live food fish.
• Limnoperna fortunei – golden mussel, native to rivers in China and south-eastern Asia but became established in Hong Kong in 1965, Japan and Taiwan in the 1990s. Subsequently invaded the United States and South America. As an efficient filter-feeder it alters communities of native macro-invertebrates which has cascading effects through freshwater food webs.
• Orconectes rusticus – rusty crayfish, native to the United States but invasive within Canada, they are large and aggressive freshwater crayfish which are more successful in deterring attack from predators than other crayfish and so their populations increase rapidly in invaded aquatic ecosystems. They outcompete native species and there is evidence of their declines where the rusty crayfish has become the dominant species.
• Plotosus lineatus – striped eel catfish, native to the Indian Ocean but first recorded in the Mediterranean in 2002 where it subsequently spread rapidly throughout the entire Israeli coast within a few years. This venomous catfish now inhabits all sandy and muddy substrates feeding on benthic species and contributing to species declines through competition and displacement.
• Codium parvulum – green alga, native to the Indo-Pacific Ocean and subsequently described from the Red Sea but since recorded off the northern shores of Israel in the Mediterranean and along the Lebanese coast. It is considered an ecosystem engineer altering the structure and functionality of ecosystems.
• Crepidula onyx – onyx slippersnail, native to the Southern coast of California and northern Pacific coast of Mexico. It is now widespread and considered highly invasive in Asia where it has been reported from Korea, Japan and Hong Kong. Slipper snails are sedentary filter-feeders and as such ecosystem engineers.
• Mytilopsis adamsi – black striped mussel described from the Pacific coast of Panama is a brackish species that invaded the Indo-Pacific Ocean during the 1900s and has reached Fiji, India, Malaysia, Taiwan, Japan, and Australia. In some of these coastal areas the species completely dominates fouling communities where it is considered to be highly opportunistic and prolific and can survive extreme environmental conditions.
• Sciurus niger – fox squirrel native to eastern and central North America, the impact of S. niger on the native western gray (S. griseus) and Douglas squirrels (Tamiasciurus douglasii) on the western United States coast is attributed to competition for resources.

Key findings include:

• The highest proportion of the species identified originate in Asia, North America and South America. 
• Aquatic species were most likely to arrive as accidental hitchhikers in or on ships (“stowaways”), while the terrestrial invertebrates were most likely to arrive as contaminants of plants.
• The Mediterranean, Continental, Macaronesian and Atlantic biogeographic regions are predicted to be the most threatened across all taxonomic groups, while the Baltic, Black Sea and Boreal regions are least at risk. The Alpine region appears not to be under threat by any species. 

The study provides a basis for full risk assessments that can comprehensively evaluate the threat posed by these species to EU biodiversity.

Sven Bacher of the University of Fribourg said: “Preventing the arrival of invasive alien species is the most effective way of managing invasions. Predicting which species are likely to arrive and survive in new regions involves considering many interacting ecological and socio-economic factors, including climate and patterns of trade. ”

Paper details
H.E.Roy, S. Bacher et al. (2018). Developing a list of invasive alien species likely to threaten biodiversity and ecosystems in the European Union. Global Change Biology.

About invasive alien species (IAS)
There are currently more than 14000 alien species recorded in Europe with more than half originating from outside EU territories, while the remainder have originated within parts of the EU and subsequently invaded others. Their numbers are rapidly increasing and in most groups so is their rate of spread. A number of alien species cause serious problems for the environment and society and these are termed invasive alien species (IAS).