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Non-Indigenous Species Thematic Assessment

Executive Summary

Non-indigenous species (NIS) may cause unpredictable and irreversible changes to marine ecosystems, such as predation of or competition with indigenous species, modification of habitats, and trophic impacts. A variety of economic or human health impacts are possible through, for example, fouling, harmful non-indigenous algal blooms or damage to structures. Of the known pathways, shipping and mariculture are responsible for most introductions into the OSPAR Maritime Area.

The results of this assessment indicate that in the last assessment period (2015-2020) there was a statistically significant reduction in introductions compared with the first assessment period (2003-2008). This indicates that the range of management measures adopted since QSR 2010 might be having a positive effect. However, there are uncertainties around monitoring effort and the timing of the data reporting for the assessment, suggesting a higher rate of introductions than was assessed for this period.

It is therefore important for OSPAR not to become complacent. With ever increasing global shipping, and the effects of climate change warming the waters of the North-East Atlantic, there is a continued risk of new non-indigenous species being translocated and establishing themselves as our climate changes. Therefore, continued and strengthened monitoring are required.

Q1. Identify the problems? Are they the same in all OSPAR Regions?

QSR 2010 provided evidence of 160 non-indigenous species in the OSPAR Maritime Area, of which 30 were identified as having an adverse impact on ecosystems or human health.

The growing demand for goods, energy and food means that the activities which provide pathways for non-indigenous species are likely to increase in the future. The introduction and translocation of non-indigenous species can cause declines in the abundance of native species, increase parasites and pathogens, negatively affect the food web, and impact on the provision of ecosystem services. Climate change, primarily increases in ocean temperature, may facilitate the introduction and establishment of new NIS as conditions become more suitable for them, as well as potential increases in global maritime trade.

Over the recent assessment period (2015-2020) the rate of introductions appears to have fallen in the Greater North Sea, Celtic Seas and Bay of Biscay and Iberian Coast, with much lower rates in the Celtic Seas. This suggests that the measures adopted are having a positive effect, although several new non-indigenous species were introduced in the OSPAR Maritime Area in the assessment period. However, there are uncertainties around the monitoring effort and the timing of the data reporting for assessments, potentially leading to a higher rate of introductions than was assessed for this period. Continued effort is required to reduce or prevent the introduction of new non-indigenous species.

OSPAR has taken action to reduce the introduction of NIS from ships’ ballast water. © Shutterstock

OSPAR has taken action to reduce the introduction of NIS from ships’ ballast water. © Shutterstock

Q2. What has been done?

Preventing the introduction of NIS is currently considered the only feasible management option for the marine environment. This is because there are limited practical and cost‐effective means available for eradicating or controlling NIS in the marine environment without harming the local ecosystem.

OSPAR has taken action to reduce the introduction of NIS from ships’ ballast water by developing general guidance on voluntary ballast water exchange (Agreements 2010-07, 2014-11) and by establishing a joint task group with HELCOM to manage non-indigenous species in relation to ballast water management exemptions and to manage ballast water and biofouling (JTG BALLAST & Biofouling). This has resulted in the adoption of the Joint Harmonised Procedure […] on the granting of exemptions under the International Convention for the Control and Management of Ship’s Ballast Water and Sediments (Agreement 2020-01) by both OSPAR and HELCOM.

The International Maritime Organization (IMO) has adopted a range of measures in relation to ballast water and biofouling aimed at reducing the risk from the transfer of non-indigenous species.

Q3. Did it work?

The assessment of the Common Indicator “ Trends in New Records of Non-indigenous Species Introduced by Human Activities ” showed an overall reduction in the rate of introduction of non-indigenous species, which indicates that the applied threshold (a decreasing trend) is generally being achieved in the assessed regions of the Greater North Sea, Celtic Sea and Bay of Biscay and Iberian Coast. Thus, while the annual rate of new non-indigenous species introduction remains high, the indication of a decreasing trend towards the most recent assessment period might suggest that the current measures have the effect of reducing the introduction and spread of non-indigenous species in the OSPAR Maritime Area. However, these findings must be used with caution due to publication lag and uncertainties in monitoring effort. Since the 2010 QSR, there has been significant progress made in the responses to address non-indigenous species; nevertheless, the introductions continue, and this issue will require continued effort to prevent further introductions.

Figure 1: The total number of new NIS records in each Region and period assessed

Q4. How does this field affect the overall quality status?

The non-indigenous species objective in NEAES 2010-2020 was to “endeavour to limit the introduction of non-indigenous species by human activities to levels that do not adversely alter ecosystems”. The evidence presented in the assessment suggests that progress has been made in terms of achieving this. However, it is also evident that the threat to marine ecosystems from non-indigenous species will remain, given the potential impact of the NIS already introduced and the increasing pressure from several activities known to be pathways for new introductions.

Q5. What do we do next?

NEAES 2030 Operational Objective S7.O2 states that by 2025, OSPAR will develop a coordinated management approach to ensure the number of non-indigenous species introduced by human activity is minimised and, where possible, reduced to zero.

Continued implementation of the joint response by OSPAR and HELCOM, the EU Marine Strategy Framework Directive (MSFD), the EU Invasive Alien Species Regulation (1143/2014) and the IMO Ballast Water Management Convention should ensure that some of the identified gaps in monitoring are addressed and should strengthen monitoring so that bias and data gaps are reduced. The potential for developing new monitoring approaches such as eDNA should be explored.

Other potential responses have been identified, including the strengthening of national biosecurity plans, consideration of NIS in relation to ecosystem restoration, addressing the issue of the potential for offshore renewables infrastructure to act as a vector for the spread of NIS, and linkage to S7.O2.

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Non-Indigenous Species Assessments


Lead author: Peter A. U. Staehr

Supporting authors: Laurent Guerin, Saa Kabuta, Ania Carbonell Quetglas, Hannah Tidbury, Frédérique Viard and Janos Hennicke

Supported by: Biodiversity Committee (BDC), Intersessional Correspondance Group on the Quality Status Report (ICG-QSR), Intersessional Correspondance Group on Ecosystem Assessment Outlook (ICG-EcoC), Intersessional Correspondance Group on Economic and Social Analysis (ICG-ESA), Climate Change Expert Group (CCEG) and the OSPAR Secretariat.


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

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