Research and analysis

Linking the presence of invasive non-native species to measures of ecological quality: summary

Published 10 May 2021

Applies to England

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This publication is available at https://www.gov.uk/government/publications/linking-the-presence-of-invasive-non-native-species-to-measures-of-ecological-quality/linking-the-presence-of-invasive-non-native-species-to-measures-of-ecological-quality-summary

Invasive non-native species (INNS) are one of the biggest threats to biodiversity, undermining the inherent resilience of ecosystems and causing significant economic costs for sectors such as agriculture and fisheries. It is vital that any tools used to assess the status of ecosystems are accurate in their representation of the ecological reality.

This project looked at what impact INNS have on the ecology of sites at which they are recorded. It also analysed whether tools the Environment Agency uses to assess the Ecological Quality Ratio (EQR) of water bodies in England under the Water Framework Directive (WFD) reflect the impacts of INNS by asking the following questions:

  • Is any effect of INNS reflected in measures of ecological status of a water body as measured by the WFD tools?
  • Which WFD tools are likely to respond to each particular INNS species?
  • Is it possible to identify when these biological tools may have ‘missed’ an impact or provided a false signal?

1. How did we assess the evidence?

A list of relevant INNS was compiled and their presence and extent in water bodies was determined from both Environment Agency and National Biodiversity Network data. Statistical analyses were applied to Environment Agency data gathered for macrophytes, fish and macro-invertebrates during long-term operational monitoring of water bodies throughout England. Analysis was conducted at two scales to increase the probability of detecting differences in measures of ecological quality and being able to attribute these to INNS:

  • Reach scale over individual years
  • Water body scale over WFD reporting periods

In both cases EQR data from sites where the INNS were present was compared to similar ‘reference’ sites where the INNS were absent.

2. Findings and implications

  • For some species our tools detect the impact of INNS and those impacts become more pronounced with the length of time the species has been present. This is shown most strongly for signal crayfish where impacts are detectable at both reach and water body scales and become greater the longer the species have been established.

  • Some of the biological tools include INNS in the EQR and that means that interpreting results is not always straightforward. The report supports previous findings that care must be taken to interpret EQR results when INNS are present. Tools such as the macrophyte tool are pressure based and so the EQR is not truly an ecological measure, rather it is a measure of nutrient EQR and was not designed to incorporate other impacts.

  • The analysis suggests that a levelling off in invertebrate NTAXA (number of taxa) scores where demon shrimp are present compared to water bodies where they are not, is due to the species constraining improvement.

3. Conclusion

These findings emphasise the need for effective monitoring since WFD tools may not detect INNS in the early stages of invasion. An understanding of these findings should lead to both a more accurate representation of the ecosystem state when making assessments using biological tools and the implementation of effective programmes of measures to help mitigate the impacts of INNS.

4. Further information

This summary relates to information from project SC170007, reported in detail in the following output:

  • Report: SC170007
  • Title: Linking the presence of invasive non-native species to measures of ecological quality
  • Project manager: David Smith/Jon Barrett
  • Research Contractors: River Communities Group, Queen Mary, University of London, Mile End Road, London E1 4NS. T: 01929 401892 Centre for Ecology and Hydrology, Maclean Building, Benson Lane, Crowmarsh Gifford, Wallingford, Oxfordshire, OX10 8BB. T: 01491 838800

This project was funded by the Environment Agency’s Chief Scientist’s Group, which provides scientific knowledge, tools and techniques to enable us to protect and manage the environment as effectively as possible.

Enquiries: [email protected]

© Environment Agency

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