Alien species and the EU Water Framework Directive: a comparative assessment of European approaches.
Although the European Water Framework Directive (WFD) does not refer explicitly to alien species (AS), it is clear that invasive AS (IAS) are considered a pressure on WFD water bodies. This article discusses the results of a questionnaire sent to all EU Member States, demonstrating considerable variability in the way that AS data are used in implementing the WFD. Responses were received from 18 countries. Most countries define AS in a similar way, but there are discrepancies, for example, in the use of historical dates to determine whether or not a species is considered non-native biogeographically. All countries have developed lists of AS, but those specific for WFD assessments are only used at present in the UK and the Republic of Ireland. Few countries monitor AS specifically for the WFD, or assess the risk that IAS are likely to cause water bodies to fail to achieve Good Ecological Status. This article discusses the results of a questionnaire sent to all EU Member States, demonstrating considerable variability in the way that AS data are used in implementing the WFD. Perhaps the most important difference among countries is in the use of AS data in WFD classification; many countries assume that classification methods take account of the impacts of AS, whereas separate 'downgrading' procedures that modify classification based on the presence and impact of IAS are used more rarely. New approaches merit further consideration, such as the application of 'biopollution indices' to highlight the impact of AS without affecting WFD classification. Alien species feature to some extent in river basin management plans, but more emphasis on action is needed. In addition, closer links with the Marine Strategy Framework Directive and with the 2014 EU Regulation on alien species are required to improve the control of aquatic AS.