Citation: Sandvik, H., A. Taugbøl,
K. M. Bærum, T. Hesthagen, T. C. Jensen,
S. I. Johnsen, O. T. Sandlund, and A. K. Schartau
(2022) Alien species and the Water Framework Directive:
recommendations for assessing ecological status in fresh waters in Norway.
Aquatic Conservation, 32, 1195–1208.
Key words: Dispersal, ecological impact, freshwater bodies,
invasive alien species, lakes, rivers.
1. Invasive alien species are recognized as a significant anthropogenic threat
to freshwater ecosystems, because they may bring about the local extinction of native
species and the collapse of habitat types of special conservation concern.
2. The Water Framework Directive (WFD) is an important legislative tool for
the protection of water bodies in the European Union. It requires the assessment of
the ecological status of water bodies and the enforcement of measures for water
bodies that fail to achieve at least "good" ecological status. However, the WFD does
not explicitly mention alien species.
3. This article presents a three‐tiered approach for the incorporation of data
on alien species into WFD assessments of freshwater bodies in Norway. If relevant data
on WFD parameters are available for the water body under consideration, its ecological
status should be inferred from those data. Otherwise, ecological status should be
assessed using evidence of the effects that the alien species have on biological
quality elements in comparable water bodies. If neither of these options is feasible,
the ecological status should be classified according to the ecological effect score
of the alien species present, as obtained from the Generic Ecological Impact
Assessment of Alien Species (GEIAA).
4. It is further recommended that a water body cannot be assigned "high ecological
status" if at least one alien species is present. If more than one alien species is
present, the status is determined by the species with the highest impact.
5. Ecological, geographical, historical, and taxonomic delimitation criteria for
this assessment method are presented, together with a list of the alien species that at
present fulfil these delimitations in Norway.
6. The management implications of the recommendations are that more Norwegian
freshwater bodies are likely to require measures, and that further data must be
collected. Most of the recommendations are transferable to other countries, although
they may require adjustment.
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