Trends in newly recorded non-indigenous species introduced by human activities
Newly introduced non-indigenous species continue to be recorded in UK waters, with 39 species reported for the first time between 2003 and 2020. No significant trend in the rate of new introductions was observed over this period. It is uncertain whether GES has been achieved for this indicator.
Assessment method
Records of new marine NIS recorded from UK waters in each of the two OSPAR regions (Greater North Sea and Celtic Seas) were requested from a network of UK experts to determine the first record of occurrence of each NIS from 2003 to 2020. Further records, and confirmation of the dates of first occurrence, were obtained by reviewing published literature, and by searching records published by the National Biodiversity Network Atlas NBN Atlas - UK’s largest collection of biodiversity information. The taxonomic range considered covers all animals, plants and algae. Cryptogenic species (i.e. species for which native or non-native status in the UK is unclear) are not included. Records from transitional waters (estuaries) are included only when the species is predominantly marine.
NIS data for introductions in the UK waters in this assessment considers the dates of records and location as the first observation in UK waters of a species. The exact date and location of the introduction (or arrival) of NIS is generally difficult to obtain. The data set collated for the new introductions in UK waters assessment can be found at Davison and others (2025).
The data analysis to identify trends in new records of introductions of NIS considers the data set from 2003 to 2020, that is relevant to three six-year assessment periods (period 1: 2003-2008; period 2: 2009-2014; period 3: 2014-2020). Non-parametric statistical analysis was used to assess differences including Mann-Kendal test to assess the existence of a significant trend.
Results
The cumulative number of newly introduced marine NIS recorded in UK waters has increased throughout the period 2003-2020 inclusive (Figure 1). A total of thirty-nine species were first recorded in one or both of the regions (Greater North Sea and Celtic Seas) during this period, of which fourteen species were recorded in both regions. There was no significant trend in the rate of new introductions each year of this reporting period, or between the three six-year assessment periods (period 1: 2003-2008; period 2: 2009-2014; period 3: 2015-2020).
Figure 1. The number of new NIS introduced per year since 2003 into UK coastal waters across three assessment periods (2003-2008), (2009-2014) and (2015-2020).
A total of seventeen species were first recorded only in the Greater North Sea area during the period 2003-2020, compared to eight species first recorded only in the Celtic Seas. Many of the species recorded in both regions were first observed in ports and marinas on the English south coast before extending their range westwards towards the Celtic Seas region, demonstrating that these sites are important hotspots for NIS introduction (although higher observer effort may also play a part in the discrepancy).
As there is no routine monitoring programme for NIS in the UK, the results should be interpreted with some caution due to the caveats involved with the data used. The dates should be regarded as the first record of a species and not the date of arrival, which is usually unknown; there will usually be a delay between the arrival of the first NIS individuals and the first recording of them. This time-lag between arrival, recording and reporting will vary according to species and location, with more noticeable and easily identifiable species at regularly visited sites being more likely to be recorded within a shorter time of their arrival. The temporal and spatial coverage of NIS recording is unevenly distributed along the UK coast, introducing uncertainties when comparing NIS introduction between regions and time periods. In this assessment (Figure 1), noticeable step increases in 2004 and 2009 relate to specific surveys of key ports and marinas which were little visited by experts in the intervening years.
Conclusions
Marine NIS continue to arrive in UK waters, with 39 species being recorded for the first time in one or both of the UK regions (Greater North Sea and Celtic Seas) between 2003 and 2020 inclusive. There was no significant trend in the rate of new introductions was observed over this period. This pattern of continued increase in marine newly introduced NIS mirrors that seen in neighbouring countries, including Netherlands and the French Channel coast (Gittenberger and others 2023, Massé and others 2023).
Data limitations in both spatial and temporal contexts from the lack of a routine risk-based monitoring programme for NIS limit the ability to accurately assess Good Environmental Status in the UK for this indicator. The cumulative increase in marine NIS present in UK waters, some of which will have environmental or economic impacts, also underlines the need to focus on methods of preventing their arrival.
Knowledge gaps
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The lack of systematic risk-based NIS monitoring in the UK marine environment is a limiting factor when assessing GES. Most newly introduced NIS records in the UK originated from opportunistic records from volunteers, or from monitoring programmes on a relatively small spatial scale, or from discrete and ad hoc studies with limited spatial and temporal scales. The UK lacks monitoring programmes for NIS at high-risk locations, which limits the power of detection at key points of introduction such as ports and harbours. There are few local scale NIS monitoring programmes that are exceptions, such as the established NIS monitoring programme in Orkney (Kakkonen and others 2019) and the NIS monitoring in Shetland Islands.
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The lack of a dedicated marine NIS data repository. There is a need for records to be consistently documented with associated data quality controls verified by experts.
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Data gaps on pathways linking to NIS introductions.
There are other knowledge gaps in terms of how marine NIS spread between UK sites, and the level of impact they have in our waters.
References
Davison, P., Matejusova, I., Garnacho, E., Barry, P., Giesler, R., Grant, L., Jones, J., Kakkonen, J., McCambridge, S., and Wood, C. (2025). Non-indigenous species introduction records in UK waters 2003 to 2020. Cefas, UK. V1. doi: https://doi.org/10.14466/CefasDataHub.168.
Gittenberger, A., Rensing, M., Faasse, M., van Walraven, L., Smolders, S., Keeler Perez, H. and Gittenberger, E. (2023). Non-indigenous species dynamics in time and space within the coastal waters of the Netherlands. Diversity, 15(6), p.719. https://doi.org/10.3390/d15060719 .
Kakkonen, J.E., Worsfold, T.M., Ashelby, C.W., Taylor, A. and Beaton, K. ( 2019). The value of regular monitoring and diverse sampling techniques to assess aquatic non-native species: a case study from Orkney. Management of Biological Invasions 10(1): 46–79. https://doi.org/10. 3391/mbi.2019.10.1.04 .
Massé, C., Viard, F., Humbert, S., Antajan, E., Auby, I., Bachelet, G., Bernard, G., Bouchet, V.M., Burel, T., Dauvin, J.C. and Delegrange, A. (2023). An overview of marine non-indigenous species found in three contrasting biogeographic metropolitan French regions: Insights on distribution, origins and pathways of introduction. Diversity, 15(2), p.161. https://www.mdpi.com/1424-2818/15/2/161
Authors
Authors: Phil Davison1, Eva Garnacho1, Iveta Matejusova2
1 Centre for Environment, Fisheries and Aquaculture Science
2 Marine Directorate of the Scottish Government
Acknowledgements: Peter Barry1, Rebecca Giesler3, Laura Grant4, Jennie Jones4, Jenni Kakkonen5, Susan McCambridge6, Hannah Tidbury1, Christine Wood7.
3 University of Highlands and Islands
4 Natural Resources Wales
5 Orkney Islands Council Harbour Authority
6 Department of Agriculture, Environment and Rural Affairs (DAERA)
7 Marine Biological Association
Assessment Metadata
Please contact marinestrategy@defra.gov.uk for metadata information
Assessment metadata
| Assessment Type | UK Marine Strategy Framework Directive Indicator Assessment |
|---|---|
Descriptor 2. Non-indigenous species do not adversely alter the ecosystem | |
Changes to non-indigenous species communities | |
OSPAR CEMAP Guidelines Common Indicator NIS3: Changes to non-indigenous species communities | |
| Point of contact email | marinestrategy@defra.gov.uk |
| Metadata date | Monday, January 1, 2024 |
| Title | Trends in newly recorded non-indigenous species introduced by human activities in the United Kingdom’s Greater North Sea and the Celtic Seas sub-regions. |
| Resource abstract | |
| Linkage | |
| Conditions applying to access and use | Crown copyright, licenced under the Open Government Licence (OGL). |
| Assessment Lineage | |
| Dataset metadata | |
| Dataset DOI | https://doi.org/10.14466/CefasDataHub.168 Non-indigenous species introduction records in UK waters 2003 to 2020 (Davison and others 2025). |
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