B6. Pressure from invasive species
a. Freshwater invasive species
b. Marine (coastal) invasive species
c. Terrestrial invasive species
Type: Pressure Indicator
This indicator was updated in 2023.
Introduction
Non-native species are those that have reached Great Britain accidentally on human transport (e.g. ships, planes), or have been deliberately introduced. Others may have arrived naturally, but from a non-native population in Europe. Species that have arrived since 1500 are included within this indicator. Most non-native species are considered benign or positive, but some have a negative impact on native species through the spread of disease, competition for resources, or by direct consumption, parasitism or hybridisation. Non-native species are considered to be ‘invasive’ if they have a negative impact on native species and a high capacity to spread to natural and semi-natural habitats.
This indicator shows the change in number of invasive non-native species established across 10% or more of the land area of Great Britain, or along 10% or more of the extent of its coastline.
Contents
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Key results
- Figure B6i. Number of invasive non-native species established in or along 10% or more of Great Britain’s land area or coastline, 1969 to 2022
- Assessment of change in the cumulative net total number of invasive non-native species established in or along 10% or more of Great Britain’s land area or coastline
- Relevance
- Background
- Goals and Targets
- Web links for further information
- References
- Downloads
Key results
There are 3,343 non-native species in Great Britain, 2,074 of which are classified as established (reproducing in the wild). This indicator contains 195 non-native species that are considered to be exerting a negative impact on native biodiversity (48 freshwater species, 39 marine species and 108 terrestrial species). The majority (189) of these species are established; six are long-term residents but not known to breed in the wild, (two species of terrapin (Emys orbicularis and Trachemys scripta) and four freshwater fish (Ameiurus melas, Leuciscus idus, Salvelinus fontinalis and Oncorhynchus gorbuschas).
Over the period 1969 to 2022, invasive non-native species have become more prevalent in the countryside. Since 1969, the number of these species established in or along 10% or more of Great Britain’s land area or coastline has increased in the freshwater, marine (coastal) and terrestrial environments, thereby increasing the likely pressure on native biodiversity (Figure B6i).
Figure B6i. Number of invasive non-native species established in or along 10% or more of Great Britain’s land area or coastline, 1969 to 2022
Notes about Figure B6i:
- Each data point reported for this indicator represents the count of invasive non-native species for the preceding 10 years rather than annual data (i.e. the data point for 1969 relates to the count of invasive species present in the period 1960 to 1969).
- The square marker on the line chart (figure B6i) shows the 2022 data point which covers a shorter time period than the triangular markers on the line chart (currently three years, 2020 to 2022).
Source: Botanical Society of Britain & Ireland; British Trust for Ornithology; UK Centre for Ecology & Hydrology; Marine Biological Association; National Biodiversity Network.
This indicator shows a count of invasive species for each decade, unlike the majority of other indicators that report annually. For example, the data point for 1969 relates to the count of invasive species present in the period 1960 to 1969. Therefore, it is only possible to assess long-term trends as there are insufficient data to establish trends over shorter time periods.
Comparing the latest data point from 2022 with the previous one, 2019, the number of invasive non-native species established in or along 10% or more of Great Britain’s land area or coastline has increased in terrestrial (from 60 to 61 species), in freshwater (from 13 to 14 species) and remained the same in marine environments (29 species).
Assessment of change in the cumulative net total number of invasive non-native species established in or along 10% or more of Great Britain’s land area or coastline
| Long term | Short term | Latest year | |
| Freshwater invasive species |
Deteriorating 1969–2022 |
Not assessed |
Not assessed |
| Marine (coastal) invasive species |
Deteriorating 1969–2022 |
Not assessed |
Not assessed |
| Terrestrial invasive species |
Deteriorating 1969–2022 |
Not assessed |
Not assessed |
Notes for Assessment of Change table:
Analysis of the underlying long-term trends is carried out by the data providers. See Assessing Indicators. Short-term trends and latest-year changes are not assessed.
Relevance
The United Nations Convention on Biological Diversity (CBD) identifies invasive non-native species as a major threat to biodiversity. Many non-native species do not threaten biodiversity, but invasive non-native species can spread disease (for example, signal crayfish, Pacifastacus leniusculus), modify ecosystems (for example, rhododendron, Rhododendron ponticum), drastically reduce populations of native species (for example, American mink, Mustela vison), or hybridise with native species (for example, ruddy duck, Oxyura jamaicensis).
Under the CBD, the United Kingdom has an international obligation to address the impacts of invasive non-native species. The UK government has published 3 strategies, with the current one starting in 2022, under the Invasive Non-native Species Framework for Great Britain.
Background
The indicator and background charts are based on species distribution data available through the National Biodiversity Network (NBN), supplemented by expert knowledge and in house datasets of the Botanical Society of Britain and Ireland (BSBI), British Trust for Ornithology (BTO), UK Centre for Ecology & Hydrology (UKCEH), the Environment Agency (EA) and Marine Biological Association (MBA). Trends in the extent of invasive non-native species, as presented in Figure B6i and B6ii were derived through a two-stage process. The number of invasive non-native species included within the indicator was substantially expanded from the 49 species used in the indicator published in 2009 (Hill et al., 2009). An initial list was derived from the GB Non-native Species Information Portal (GB-NNSIP) (Roy et al., 2014) by selecting all non-native species within the database that are noted to have, or potentially have, a negative or strongly negative ecological effect, including all 49 species from the original indicator. This list was subsequently reviewed by experts. Species for which there was a high degree of uncertainty with respect to negative impact were removed and new species were added as deemed appropriate. The revised list in 2014 comprised of 179 species, but has been subsequently amended in 2015, 2017, 2018, 2019, 2020, 2021, 2022 and 2023 to now comprise of 195 species (see technical background document).
Invasive non-native species were categorised according to the extent of the land area or coastline of Great Britain in which they were found in the decades of 1960 to 1969, 1970 to 1979, 1980 to 1989, 1990 to 1999, 2000 to 2009, 2010 to 2019 and the present period of 2020 to 2029 (see Table B6i). The categorisation was achieved by combining assessment of modelled distributions based on data available from the NBN with expert opinion and the use of additional datasets where available (for more details see the technical background document).
Table B6i. Invasion extent of non-native species
|
Definition |
Interpretation |
Extent |
|
Not present in territory |
Absent |
0 |
|
Present in territory and either not established or with established populations that have not spread more than 10 km from their source |
Not or scarcely established |
1 |
|
Established populations represent less than 10% of territory, with some having arrived from further than 10 km from their source; or if more widespread then populations scattered and sparse |
Established but still generally absent or at most occasional |
2 |
|
Established populations present in 10% to 50% of the territory |
Established and frequent in part of the territory |
3 |
|
Established in more than 50% of the territory |
Widespread |
4 |
Figure B6ii. Changes in the extent (as listed in table B6i) of invasive non-native species in freshwater, marine (coastal) and terrestrial environments of Great Britain, 1969 to 2022
Notes about Figure B6ii (a, b, c):
- Each data point reported for this indicator represents the count of invasive non-native species for the preceding 10 years (i.e. the data point for 1969 relates to the count of invasive species present in the period 1960 to 1969).
- The 2022 data point covers a shorter time period (2020 to 2022) than the previous data points.
- Extent level ranges from 1 (Not or scarcely established) to 4 (Widespread) (see Table B6i).
Source: Botanical Society of Britain & Ireland; British Trust for Ornithology; UK Centre for Ecology & Hydrology; Marine Biological Association; National Biodiversity Network.
The indicator is compiled from those invasive non-native species established in or along 10% or more of Great Britain’s land area or coastline (that is, extent categories three and four). There are limitations to this approach:
- The list of invasive non-native species has been derived through the rapid assessment of impacts based on expert opinion. A semi-quantitative approach is currently being developed to improve the certainty and reliability of the list.
- The extent value is based on relatively broad categories. The extent of some species can increase multi-fold within a single category, for example, the number of invasive non-native species in 10% to 50% of the land area of Great Britain, which can reduce the sensitivity of the indicator.
The occurrence data obtained from the NBN may not be representative of the species distribution in each decade, especially for both the earlier and most recent time periods, because there is often a time lag before occurrence data appear on the NBN. Furthermore, the availability of occurrence data reflects the intensity of survey effort applied in a time period that has subsequently been submitted to the NBN. The attribution of extent categories has, however, been supplemented by expert opinion and in some cases by more complete datasets.
Goals and Targets
The UK and England Biodiversity Indicators are currently being assessed alongside the Environment Improvement Plan Targets, and the new Kunming-Montreal Global Biodiversity Framework Targets, when this work has been completed the references to Biodiversity 2020 and the Aichi Global Biodiversity Framework Targets will be updated.
Aichi Targets for which this is a primary indicator
Strategic Goal B. Reduce the direct pressures on biodiversity and promote sustainable use.
Target 9: By 2020, invasive alien species and pathways are identified and prioritized, priority species are controlled or eradicated, and measures are in place to manage pathways to prevent their introduction and establishment.
Aichi Target for which this is a relevant indicator
None
Web links for further information
- Developing an indicator of the abundance, extent and impact of invasive non-native species (PDF, 382kb)
- Delivering Alien Invasive Species Inventories for Europe (DAISIE)
- EU Invasive Alien Species – Regulation
- NBN Atlas
- GB Non-native Species Secretariat
- The Invasive Non-native Species Framework Strategy for Great Britain
References
Hill, M. O., Beckmann, B. C., Bishop, J. D. D., Fletcher, M. R., Lear, D. B., Marchant, J. H., Maskell, L. C., Noble, D. G., Rehfisch, M. M., Roy, H. E., Roy, S. & Sewell, J. (2009). Developing an indicator of the abundance, extent and impact of invasive non-native species. Final report. Defra.
Roy, H. E., Preston, C. D., Harrower, C. A., Rorke, S. L., Noble, D., Sewell, J., Walker, K., Marchant, J., Seeley, B., Bishop, J., Jukes, A., Musgrove, A. & Pearman, D. (2014). GB Non-native Species Information Portal: documenting the arrival of non-native species in Britain. Biological Invasions, 16(12), 2495–2505.
Downloads
Download the Datasheet and Technical background document from JNCC's Resource Hub.
Last updated: November 2023
Latest data available: 2022
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