• Latest Version, 2024 Assessment
• 2018 assessment

Non-indigenous species

The extent to which Good Environmental Status has been achieved

The achievement of Good Environmental Status (GES) with respect to non-indigenous species (NIS) is uncertain for both the Celtic Seas and the Greater North Sea due to data limitations and a lack of comprehensive NIS monitoring in UK waters.  

Progress since previous assessments

The progress towards GES for NIS is still uncertain. The present assessment concurs with the previous assessment, indicating that the cumulative numbers of NIS arriving to the UK continue to rise. However, there is no significant trend in the rate at which new NIS are introduced over the previous and current assessment periods from 2003 to 2008, 2009 to 2014 and 2015 to 2020.  

Confidence in the assessments remains low due to data limitations that were identified since the previous assessment. This highlights the need to improve the accuracy of existing data and its availability. Designing and implementing UK wide routine monitoring programmes is necessary to generate the data necessary to allow future assessments. 

The conclusions drawn, using the UK Marine Strategy assessment area, omit data from transitional waters. These contain some high-risk locations for NIS introduction and spread, such as marinas and aquaculture sites. 

Terminology used in this assessment: The term ‘non-indigenous species’ (NIS), as used by The Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR) Commission and the UK Marine Strategy (UKMS), is used throughout this thematic assessment. This is the equivalent of ‘alien species’ (as used by the Convention on Biological Diversity (CBD)) and ‘non-native species’. It refers to a species intentionally or unintentionally introduced outside its native range by human actions. An ‘invasive non-native species’ (INNS) is any non-native animal or plant that has the ability to spread, causing damage to the environment, the economy, our health, or the way we live. 

How progress has been assessed

Assessment overview

GES for NIS is determined using two indicators (Table 1). These indicators measure trends in numbers of newly introduced NIS in marine ecosystems (Criteria 1) and numbers of new populations of established invasive NIS (Criteria 2). There are currently no threshold values for either of the indicators which would indicate GES for NIS, so only increasing or decreasing trends in the number of new species or new populations are assessed.  

Table 1. Summary overview of the status for NIS (D2), GES target, criteria, and indicator assessments  

Overarching target: The rate of introduction of NIS, spread and impact of invasive NIS caused by human activities is not adversely altering ecosystems.  

Criteria 1	The introduction of NIS by human activities does not adversely alter the ecosystem
UKMS 2019 Target	The number of newly introduced NIS caused by human activities is minimised and, where possible, reduced to zero
Corresponding OSPAR Quality Status Report (QSR) 2023 Indicator	The number of newly introduced NIS
Greater North Sea	Uncertain
Celtic Seas	Uncertain
Criteria 2	The spread of established invasive NIS does not adversely alter the ecosystem
UKMS 2019 Target	The rate of spread of established invasive NIS, as a result of human activities, is minimised and reduced where possible
UK Only Indicator	The number of new populations of established invasive NIS
Greater North Sea	Uncertain
Celtic Seas	Uncertain

The environmental targets for marine NIS have been developed in the context of the increased importance of managing the pathways and vectors which facilitate the introduction and spread of NIS, as prevention is the most effective management method to avoid the impacts they may cause (HM Government, 2012). Although there are indicators for new introductions and spread of NIS, there is no indicator available to measure impact.  

Detailed assessments

NIS are species that are introduced outside of their natural range by human activities. This can result in pressures or impacts in the environment through competition for resources and space or causing wider changes in the marine ecosystem.  

In UK waters, GES in relation to NIS was assessed by two indicators: ‘Trends in new records of non-indigenous species introduced by human activities’ (i.e. newly recorded NIS – OSPAR common indicator) and ‘The number of new populations of established invasive NIS’ (i.e. ‘NIS spread’- UK only indicator). The NIS spread was assessed for the first time. The UK assessment time frame spanned 2003 to 2020, representing three six-year assessment periods. Data for UK waters for each indicator were collated from multiple sources and reviewed by experts to represent the UK Marine Strategy Spatial remit (i.e. including coastal waters but excluding transitional waters). Details of the data and methods used are provided in each indicator assessment linked below.  

Indicator 1 - NIS new introductions 

The cumulative number of newly introduced NIS rose throughout the reporting period. UK records show a total of 53 new NIS recorded for the first time between 2003 to 2020 in UK waters in the Greater North Sea or Celtic Seas (Figure1). There were 39 unique species reported, with 14 species first recorded in both areas during the assessment period. Each of these NIS is now considered either as being established in UK waters, or to have high potential to establish.

Figure 1. The number of new NIS introduced per year since 2013 into UK coastal waters across three assessment periods  (2003-2008), (2009-2014) and (2015-2020).  

Newly introduced species. The number of new species introduced continued throughout the assessment period of 2003-2020. There was no significant trend in the rate of new introductions each year of reporting period, or between the three six-year assessment periods (period 1: 2003-2008; period 2: 2009-2014; period 3: 2014-2020). 

These results for the UK are different from those reported in the OSPAR QSR (2023) assessment for both regions. The QSR 2023 assessment concluded that there is a decreasing trend in the rates of NIS introduction in both Greater North Sea and Celtic Seas, based on data sets submitted from all contracted parties in each region.  

Indicator 2- NIS spread 

This indicator assessment estimates the rate of spread of thirteen established high-impact NIS that are considered invasive and listed on the UK Marine NIS Priority List (external link). Their establishment in other areas and habitats could have a negative impact. The rate of their spread was estimated through quantification of the relative change in the number of 10km grid cells they occupied within UK coastal waters (excluding transitional waters) over the reporting period.  

The outcome of the analysis was species dependent. A decreasing rate of spread from 2003 to 2020 was reported for five established NIS (Caprella mutica, Crepidula fornicata, Sargassum muticum, Solidobalanus fallax and Styela clava); while increasing rate of spread was seen for Grateloupia turuturu. No significant change in the rate of spread was found for the remaining seven species (Bonnemaisonia hamifera, Diadumene lineata, Ensis leei, Ficopomatus enigmaticus, Magallana gigas, Undaria pinnatifida and Urosalpinx cinerea).  

Limitations of NIS assessment for both indicators 

The lack of a routine risk-based monitoring programme for NIS in the UK means that data available for the assessment were limited in both spatial and temporal contexts. The survey effort between years is not comparable as there are no prescribed site visits every year, no list of agreed species for which presence and absence data are recorded, and there is no consistent methodology used across surveying organisations. Additionally, some NIS records reach the relevant databases, or appear in databases, with a substantial delay.  

The results of this assessment should be interpreted with the following set of caveats:  

• In most cases, there will be a delay between the arrival of the first NIS individuals and time when the population is large enough for it to be found using current monitoring efforts and the methodology used. Consequently, the data in this assessment should be regarded as the date of first record and not the date of introduction. 

• This time-lag between introduction, recording, and reporting will depend on frequency of monitoring at each location. NIS hotspots are not monitored on an annual basis. The noticeable step increase in the number of new species reported for example in 2004-2005 is most likely due to a specific survey of key ports and marinas undertaken by the Marine Biological Association (external link) in those years. A further step increase can be seen in 2009-2010 when a survey of the same sites was repeated (Bishop et al., 2015).  

• The time-lag between introduction, recording, and reporting will also vary between species, depending on survey methodologies and the surveyors’ expertise in finding and identifying certain species. The majority of recorded marine NIS belong to relatively well-studied groups such as benthic crustaceans, molluscs, tunicates, and bryozoans which are likely to be found and identified by the survey methods used. Less-studied groups such as planktonic species, polychaete worms and algae are intrinsically less likely to appear in this dataset due to difficulty of capture without specialist methods, difficulty in identification, or difficulty in assigning non-native status to UK records due to poorly understood native ranges. 

• Exact dating of the first UK records for species might need continuous adjustment. There are several examples in this dataset where first records were backdated, based on results of delayed analysis of archive material.  

Achievement of targets and indicators used to assess progress in 2024

NIS spread

Newly recorded non-indigenous species

 

Drivers, activities and pressures affecting the state of the marine environment

The key drivers and activities are maritime traffic, aquaculture, and the presence of artificial hard substrate structures at sea. Available data indicate that maritime traffic associated with cargo, fishing, military, and recreational vessels is likely the major pathway for NIS introduction and spread in the reporting period. This would include transport of NIS as biofouling on ship hulls or in ballast water.  

Aquaculture (including fish, shellfish, and seaweed farming; also termed ‘mariculture’ in marine environments) is a pathway for introduction and spread of NIS, both as the target species for farming and as accidental contaminants.  

Increasing demands for energy are resulting in the introduction of more hard substrate structures to the marine environment (e.g. infrastructure for renewable energy, and the oil and gas industries) which may facilitate the establishment and spread of NIS. Currently, these installations are not monitored, or data is not made available, and this represents a significant gap in data.  

Impact of pressure on ecosystem services

NIS are known to impact negatively on native species and communities through competition for space or resources, degradation of habitat, alteration of food webs, predation, and disease introduction. Aquaculture production can be negatively affected by fouling NIS, resulting in clean-up costs, reduced yields, and potential stock movement restrictions. Another impact of NIS is on commercial and fishery species through competition or hybridisation. NIS can impact human wellbeing, through their effects on valued habitats and features, and environment aesthetics.  

Impacts of climate change on pressures and state

Climate change, primarily ocean temperature increases, may facilitate the establishment of introduced NIS and unaided dispersion of NIS, particularly for warmer water species. Climate change may also lead to changing patterns in international trade and shipping activity, resulting in new pressures in different geographic areas. Resilience of ecosystems to invasive species might be weakened by climate change. Coastal protection created to mitigate against sea-level rise due to climate change, such as sea walls and breakwaters, provides additional hard structures and therefore might promote NIS establishment and spread. The expansion of energy infrastructure at coastal and offshore areas, as one of climate change mitigation, might facilitate the introduction and spread of new species by creating hard substrate stepping stones for NIS.  

Management actions taken

Management measures currently applied are focussed on prevention of NIS introductions, including pathway management and biosecurity, via mechanisms such as biosecurity campaigns, toolkits and plans, as well as codes of practice and relevant legislations. 

The International Maritime Organisation have adopted measures in relation to ballast water and biofouling under the  International Convention for the Control and Management of Ships' Ballast Water and Sediments and Voluntary IMO Hull Fouling Guidelines to limit introductions via shipping. More recently, the UK has developed the voluntary Recreational Boating and Angling Pathway Action Plans, and has implemented the International Ballast Water Convention’s requirements through the Merchant Shipping (Control and Management of Ships’ Ballast Water and Sediments) Regulations .  

Legislation varies between regions; the Scottish Government introduced a code of practice on Non-Native Species in 2012, and relevant bodies are able to set out measures to control or eradicate NIS through voluntary Species Control Agreements and mandatory Species Control Orders. In England and Wales, the Invasive Alien Species (Enforcement and Permitting) Order 2019 aims to prevent and minimise the impact of the introduction and spread of a restricted list of high priority species. Currently, there is no reliable data on uptake of these guidelines, codes and regulations and their effectiveness has therefore not been assessed for this reporting period.  

Next steps

Evidence challenges

• The lack of systematic risk-based NIS monitoring in the UK marine environment is the main limiting factor for accurate, evidence-based assessment of GES with respect to NIS. Currently, most new species are recorded opportunistically by volunteers, or from monitoring programmes on a relatively small spatial scale (for example, regular monitoring in Orkney), or from discrete and ad hoc studies with limited spatial and temporal scales. 

• Without standardisation there is low confidence in the trends observed for two NIS GES indicators. Reporting NIS absence as well as presence is essential to distinguish between true trends observed and biases resulting from changes in monitoring efforts. Development of improved statistical approaches to quantify changes in monitoring effort and trends in NIS GES indicators is needed to improve confidence of future assessments.  

• The lack of a dedicated NIS marine data repository, with records verified by experts and agreed reporting workflows with data quality controls leads to delays and gaps in NIS records. 

Operational objectives

• We will progress the recommendations of the UK Marine INNS Task and Finish Group (to be agreed in 2025) to improve management of pathways (aquaculture, recreational boating, and ballast water) by which new NIS are arriving.  

• We will complete, and then review and refine where necessary, Pathway Action Plans on angling and recreational boating to reduce the risk of introduction and spread of marine NIS.  

• We will work towards delivering a programme of standardised monitoring surveys with appropriate spatial and temporal coverage to provide adequate data and improve confidence in future assessments.  

• We will continue with work on identifying NIS hotspots for surveillance, development of DNA-based monitoring tools for marine NIS, and improving NIS data repositories and reporting workflows. 

• We will work nationally and with other countries, particularly those in OSPAR, to establish threshold values for NIS indicators.  

Technical Detail: Good Environmental Status for the next cycle

Table 2 shows the overarching targets (characteristics) for GES, along with their criteria, individual GES targets and associated indicators for the next assessment cycle (subject to change following the UKMS Part 1 public consultation). 

Table 2. GES criteria and targets for NIS for next assessment cycle. 

Overarching target: The rate of introduction of NIS, spread and impact of invasive NIS caused by human activities is not adversely altering ecosystems. 

Criteria	2024-2030 GES targets	Comment	Indicators
Newly introduced NIS	The number of newly introduced NIS, as a result of human activities, is minimised and where possible reduced to zero	No change in the target.	The number of records of newly- introduced NIS
The spread of established invasive NIS	The rate of spread of established invasive NIS, as a result of human activities, is minimised and reduced where possible	No change in the target.	The number of populations of established invasive NIS

 There is no indicator to assess impacts of established NIS. 

References

Bishop, J.D., Wood, C.A., Yunnie, A.L. and Griffiths, C.A. (2015). Unheralded arrivals: non-native sessile invertebrates in marinas on the English coast. Aquatic Invasions, 10(3), 249-264. 

HM Government (2012). Marine Strategy Part One: UK Initial Assessment and Good Environmental Status. 163 pp.  

OSPAR (2023). Non-Indigenous Species Thematic Assessment. In: OSPAR, 2023. Quality Status Report 2023. OSPAR Commission, London.  

Contributors

Authors: Phil Davison¹, Eva Garnacho¹, Hannah Tidbury¹, Iveta Matejusova² 

¹Centre for the Environment, Fisheries and Aquaculture Science,² Marine Scotland Science 

Acknowledgements: Peter Barry, Rebecca Giesler, Laura Grant, Jennie Jones, Jenni Kakkonen, Susan McCambridge, Christine Wood.