Environmental risk assessment for invasive alien species: A case study of apple snails affecting ecosystem services in Europe

The assessment of the risk posed by invasive alien species (IAS) to the environment is a component of increasing importance for Pest Risk Analysis. Standardized and comprehensive procedures to assess their impacts on ecosystem services have been developed only recently. The invasive apple snails (Pomacea canaliculata and P. maculata) are used as a case study to demonstrate the application of an innovative procedure assessing the potential impact of these species on shallow freshwater ecosystems with aquatic macrophytes in Europe. The apple snail, Pomacea maculata, recently established in the Ebro delta in Spain resulting in a serious threat to rice production andwetlands, having also a high risk to spread to other Europeanwetlands. Here, the population abundance of apple snails is regarded as themain driver of ecosystemchange. The effects of ecosystemresistance, resilience and pestmanagement on snail population abundance are estimated for the short (5 years) and the long (30 years) term. Expert judgment was used to evaluate the impacts on selected ecosystem services in a worstcase scenario. Our study shows that the combined effects of apple snails are estimated to have profound effects on the ecosystem services provided by shallow, macrophyte-dominated ecosystems in Europe. This case study illustrates that quantitative estimates of environmental impacts fromdifferent IAS are feasible and useful for decision- makers and invasive speciesmanagers that have to balance costs of control efforts against environmental and economic impacts of invasive species.