Alien Organisms and trade in Endangered Species (CITES)
Report no: 2017: 33
11 species of alien terrestrial snails have the potential to establish a population in Norway, given a warmer climate in the next 50 years. The potential impact include harming local flora and native snails and slugs. They may also harm crops.
This is the conclusion of the risk assessment of the Scientific Committee for Food and Environment (VKM), which has assessed the risks to the Norwegian biodiversity associated with import and keeping of terrestrial gastropods.
The assessment was conducted on request from the Norwegian Environment Agency based on several applications regarding import of terrestrial gastropods intended for private, indoor, keeping, following the entry into force of the Regulations relating to alien organisms under the Norwegian Nature Diversity Act on January 1st.2016.
VKM has determined which species of terrestrial gastropods that are relevant for trade in Norway, and assessed what properties of the species and the environment that determines whether a species can establish and spread in Norway. Their potential impact was also assessed.
The assessment was conducted with a 50-year perspective, taking climate change into account.
VKM has considered 116 species. 83 come from tropical or subtropical climate, and their establishment in Norway was deemed very unlikely based on the climate conditions in their native range. These species were not assessed further as we concluded that they pose minimal threat to Norwegian biodiversity due to their low establishment potential.
33 species inhabits areas with a climate more similar to the Norwegian climate, in a 50-year perspective.18 of these were assessed as having a low risk in terms of negative impact on Norwegian biodiversity, whiletenspecies have a medium risk, and only a single species was classified as having a high risk.
- For the ten species with medium risk, today’s climate is most probably too cold for these to survive. If climate change results in increased temperatures, as predicted by the Climate Panel, we believe these have the potential to survive in Norway. If they are able to establish populations here, they might have negative impact on the local flora and native snails and slugs, in addition to damage on crops, says Anders Nielsen, who has led the scientific part of the project.
The greatest risk is posed by the European Brown Garden Snail (Helix aspersa).
- This species is known to be highly invasive, and has spread to many new areas around the world, and has had a huge impact on the environments there. It is considered to be a garden and agricultural pest in many areas where it has been introduced, and can act as a host for parasites that can infect both gastropods, birds and mammals, says Dr. Nielsen.
There was some lack of information for most of the species that was assessed. Especially for species that inhabit a climate resembling the Norwegian one, it is important to obtain information regarding what range of temperatures that can tolerate. As this information tends to be missing, the risk assessment for some of the species is associated with high uncertainty.
This lack of information is not critical for the tropical and subtropical species.
The Panel on Alien Organisms and Trade in Endangered Species is responsible for this report.