Incorporating Invasive Alien Species into Ecological Assessment in the Context of the Water Framework Directive

Abstract

The Water Framework Directive (WFD) is currently the principal document covering the management of inland, transitional and coastal waters in the EU. The current approach to its implementation regarding ecological assessment using biological elements is to develop assessment systems tailored to detect a response to a specific pressure. Although the WFD does not specifically mention invasive alien species (IAS) discussion has commenced on how to incorporate them into ecological assessment owing to their ability to significantly alter the structure and functioning of aquatic ecosystems. A potential framework is presented whereby IAS are treated as both a pressure and as part of a biological element to be monitored. It is proposed that the densities and distribution of IAS in water bodies are matched to normative definitions for quality classes in the WFD by expert groups at EU level. This would allow a rapid and consistent assignment of ecological status on the basis of IAS abundance and distribution in a water body. Such assessment should deal with IAS separately from other pressures. This would allow a separate report of the ecological degradation resulting from IAS so that specific management measures may be designed.