Indicator Specification

Trends in marine non-indigenous species

Indicator Specification
  Indicator codes: MAR 002
Published 03 Mar 2015 Last modified 10 Dec 2019
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This indicator shows the cumulative number and rate of introductions of marine Non-Indigenous Species (NIS) recorded in the regional seas of Europe since 1950. 

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Justification for indicator selection

Biological invasions are widely recognised as one of the main threats to biodiversity next to habitat destruction and pollution. Non-indigenous species (NIS), also known as alien, are species introduced outside their natural environment. They are referred to as 'invasive alien species' (IAS) if they find adequate conditions to survive, reproduce, spread, and cause widespread harm to biodiversity and human livelihood. 

The introduction of alien species is closely linked to the increasing globalisation of trade and travel. The development of maritime activities has also provided new and enhanced pathways for the spread of alien invasive species. While many of these species become part of the ecosystem they are introduced into, only a few actually become invasive and cause negative impacts. These impacts can range from reducing genetic variation and eroding gene pools to the extinction of endemic species, and the alteration of habitat and ecosystem functioning. Alien species can also hamper human activities and livelihoods that use or depend on the ecosystem, including shipping, fisheries, aquaculture production, recreation and tourism. They can also represent a threat to public health. Even when introduced locally, the impacts of marine invasions are generally widespread and irreversible. Invasive alien species can therefore cause significant ecological, economic, or social effects, threatening biodiversity and ecosystem services.

Impacts on local ecosystems are, however, still poorly assessed. The ecological impacts of invasions are often inferred from distribution data under the assumption that the more abundant the alien species, the more severe the impact. In the absence of data on both trends and impacts of invasive alien species in European seas, trends in marine NIS (i.e. all introduced species which have the potential to become invasive) are used as a proxy. 

Scientific references

Indicator definition

This indicator shows the cumulative number and rate of introductions of marine Non-Indigenous Species (NIS) recorded in the regional seas of Europe since 1950. 


The unit of measurement is the number of NIS per taxonomic group (primary producers, invertebrates and vertebrates) at Pan-European and regional sea levels.


Policy context and targets

Context description

There is currently no EU framework for tackling Invasive Alien Species (IAS) comprehensively. Current legislation is considered fragmented and addresses only a few IAS, mostly targeting disease agents and pests of animals and their products. For the marine environment, these are covered in particular by the animal health regime (various regulations and directives) and the Regulation on the use of alien and locally absent species in aquaculture. More broadly, the Birds Directive, the Habitats Directive, the Water Framework Directive (WFD) and the Marine Strategy Framework Directive (MSFD) require the restoration of ecological conditions and refer to the need to take IAS into consideration. Nevertheless, it was considered that this existing union action left most IAS unaddressed.

The European Commission formally recognised the urgent need to tackle invasions in Europe in its Communication 'Towards an EU Strategy on Invasive Species', in 2008. The EU Biodiversity Strategy, which translates the international commitments adopted by the parties to the Convention for Biological Diversity in 2010 in Nagoya, Japan, further identified combating IAS as key to safeguard European biodiversity, and sets a dedicated target and actions. In particular, it identified the need for a specific EU legislative instrument that could tackle outstanding challenges relating, inter alia, to IAS pathways, early detection and response and containment and management of IAS. As a result, in 2014, the European Commission adopted a Regulation on the prevention and management of invasive alien species in Europe. It aims to bring a more comprehensive approach to deal with IAS in Europe, across all environments. This regulation should therefore be able to integrate and ensure consistency of existing EU, global, regional and national initiatives in order to increase their effectiveness in combating invasive alien species.

The four Regional Sea Conventions have also been active in developing regional action to address non-indigenous species and are increasingly streamlining their efforts with relevant EU policy implementation. Synergies in the work to implement the ecosystem approach, taking into account the HELCOM Roadmap are discussed between HELCOM and OSPAR, Bonn Agreement, Black Sea Commission and ICES Joint Assessment and Monitoring Programme (JAMP), sets the basis on which the OSPAR Contracting Parties will work together in fulfilling these obligations over the period from 2010 until 2014. UNEP/MAP (2014) is setting a monitoring protocol to be implemented by contracting parties for producing the data necessary to calculate the non-indigenous species trend indicator. The Black Sea Commission is also working on MSFD Guiding Improvements In The Black Sea Integrated Monitoring System (MISIS).

OSPAR continues its close cooperation with the Helsinki Commission in the Baltic Sea on the development and adoption of Joint Guidelines on the granting of exemptions from the International Maritime Organisation Ballast Water Management Convention, allowing a consistent approach across Northern Europe to minimise the risk of introduction of non-indigenous species.


The EU Biodiversity Strategy to 2020 and its target 5 on combating invasive alien species (IAS) determines that: “By 2020, Invasive Alien Species and their pathways are identified and prioritised, priority species are controlled or eradicated, and pathways are managed to prevent the introduction and establishment of new IAS”.

The MSFD's main objective is to reach Good Environmental Status (GES) of the marine environment by 2020. It has 11 environmental quality descriptors to determine GES. Descriptor 2 addresses non-indigenous species: “Non-indigenous species introduced by human activities are at levels that do not adversely alter the ecosystems”. The initial reporting of Member States in 2012 has not allowed to establish adequate or regionally coherent environmental targets. These are currently being discussed.

Related policy documents

Key policy question

Are marine non-indigenous species increasing in European Seas?



Methodology for indicator calculation

Data sources

Data on marine Non-Indigenous Species is retrieved from several sources, namely: 

a) most recent updates of European online databases (i.e. DAISIE, NOBANIS, ESENIAS, AquaNIS);

b) annual reports of the ICES Working Group on the introduction and transfers of marine organisms and ICES/IOC/IMO Working Group on Ballast and Other Ship Vectors. The group meets annually and functions through extensive collaboration by expert scientists from all over the world, representing leading knowledge and expertise on this topic. They keep annual records on new invasions in the ICES area and provide management advice upon request;

c) results of the main European research projects (such as PERSEUS, COCONET, VECTORS);

d) revision of scientific publications; and

e) consultation with international and national experts.

All data is stored in a regularly updated working database maintained by the Hellenic Center for Marine Research (HCMR - presently not available online – contact Argyro Zenetos, containing more than 7800 records for over 2490 aquatic species (freshwater species included). These records were harmonised in 2009 with those contained in the main European marine alien species, as part of the Streamlining European 2010 Biodiversity Indicators (SEBI 2010) project.


Geographical aggregation and respective country data availability

Marine and estuarine species data was extracted from the working database and grouped by country at Pan-European level (i.e. EU and non-EU). Country data was further aggregated at regional sea level, following the geographical delineation of the regional seas surrounding Europe.

Country data was available at the regional sea level as follows:

Baltic Sea: EU (Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Sweden) + Russia

Greater North Sea: EU (Denmark, France, Germany, Netherlands, Sweden, UK) + Norway

Celtic Sea: EU (Ireland, UK)

Bay of Biscay & Iberian Coast: EU (Portugal, Spain, France)

Western Mediterranean Sea: EU (Spain, France, Italy) + Monaco, Algeria, Morocco, Tunisia

Ionian Sea and the Central Mediterranean Sea: EU (Greece, Italy, Malta) + Albania, Libya, Tunisia

Adriatic Sea: EU (Croatia, Italy, Slovenia) + Albania, Montenegro

Aegean-Levantine Sea: EU (Greece, Cyprus) + Egypt, Israel, Lebanon, Palestine, Syria, Turkey

Black Sea: EU (Bulgaria, Romania) + Georgia, Russia, Turkey, Ukraine

Iceland Sea: Iceland


Species filtering and taxonomic aggregation

For each regional sea, marine and estuarine species were grouped by selected taxonomic groups: vertebrates, invertebrates and primary producers (i.e. Chromista, vascular plants, algae and fungi). Estuarine species are those aquatic species that do not complete their entire life cycle in freshwater. Birds have been excluded from calculations. Established, non-established and cryptogenic species are included. Species currently reported as "extinct" in the literature and those considered to be observed due to natural or climate-driven expansion from one regional sea to the neighbouring one are excluded from calculations.


Data analysis

Individual species records were analysed to determine the year of first sampling from the environment (or first reporting when the former is missing), for each regional sea separately. For the Pan-European analysis, the very first sampling or reporting date is used.

Data is then calculated to show the cumulative number of non-indigenous species and the rate of new introductions, presented per decade since 1950. The total number of NIS recorded up until 1950 is also presented. These analyses are made both at Pan-European level and per regional sea. Non-indigenous species that have been registered in more than one regional sea have been recorded in each of them. This means regional assessments don't add up to the Pan-European assessment since the latter only considers species once. Moreover, NIS that have been recorded but with an unknown year of introduction were nevertheless considered when providing the total number of NIS, both at the Pan-European and regional sea levels.

Care has been taken to ensure that the nomenclature problems encountered have not resulted in multiple separate recordings (e.g. the same species recorded in different regions or species lists, data bases with different synonyms for the same species). Recent scientific literature was consulted to solve taxonomic problems and revise nomenclature in some cases (i.e.Marenzelleria, Mnemiopsis). Thus, some species reported as alien in national databases have been excluded as native ones. Synonyms of species reported differently in existing European systems have been sorted by using the nomenclature of WoRMS (World Registry of Marine Species) - WoRMS Editorial Board (2014). Available at 

Methodology for gap filling

When the exact date of the first sampling of a non-indigenous species is not known, the year of the relative publication has been used instead.

Personal communication with national and taxonomic experts was carried out when relevant to verify the data.  The following experts were contacted:

Belgium: Sonia VANDERHOVER, Etienne BRANQUART, Francis KERKOFF

Denmark: Kathe Rose JENSEN, Mads THOMSEN

Estonia: Henn OLJAVEER, Andres JAANUS

Finland: Maiju LEHNAMEN, Reetta LJUNGBERG

France: Marc VERLAQUE, Philippe GOULLETQUER, Laurence MIOSSEC

Germany: Ralf BANSTROP, Stephan GOLLASCH, Stefan NEHRING

Italy: Adriana ZINGONE, Carla MORRI

Lithuania: Anastasia ZAIKO

Malta: Patric SCHEMBRI

Netherlands: Rob LEWIS, Hans De BAUWE, Marco FAASE, Herre STEGENGA, 'Arjan GITTENBERGER

Norway: Vivian HUSA 


Portugal: Anna AMORIM



Turkey: Melih CINAR


Methodology references



Methodology uncertainty

The year of introduction is based on the first sampling date or reported date of the species, but it does not necessarily imply the real year of introduction. This may have happened earlier.

For the last four years (2011-14) of the analysis, the number of recorded species is an underestimate. This is due to the time lag between the sampling of the non-indigenous species and the publication of the data, which can take several years.

Data sets uncertainty

Data sets on non-indigenous species in official sources such as NOBANIS, HELCOM and AquaNiS are often contradictory. This is mainly due to the fact that these sources include freshwater species, which are encountered in the upper estuarine reaches (oligohaline waters with salinities < 5ppt), in their inventories. 

Geographical discrepancies between regional or national sources of data and those presented here may occur, namely in the North Sea. These arise from the definition of the borders between regional seas, which may not concur with the map of regional seas around Europe used in this indicator. Individual experts were also contacted in many cases.

In the Black Sea, divergence between the regional experts used for reference makes the compilation of an agreed list impossible at the moment. As a result, the number of marine invertebrates (mostly copepods) and fish are considered to be over-estimated and need further revision. Moreover, six species which were intentionally imported for aquaculture are not included as they are mostly freshwater species (see Yankova et al., 2014). Cryptogenic species are included by most scientists but excluded by others as native. In many cases historical introductions such as the ship worm Teredo navalis are not perceived as aliens and not included in lists. Species reported from drift material washed ashore are included as casual records.

The list for Mediterranean alien species is still an underestimate as it does not include monocellular algae. The diversity of marine microalgae is scarcely known in wide areas of the Mediterranean Sea. This makes it difficult to determine if a suspected microalgal invader was already present as part of the rare, hidden and un-sampled phytoplankton. Therefore phytoplankton has not been included in the analysis of the indicator.  

The uncertainties behind data sets on non-indigenous species reflect the challenge of adequately discovering and reporting new species or mapping their distribution, but also of compiling data at a national level.



Yankova, M., Pavlov, D., Ivanova, P., Karpova, E., Boltachev, A., Öztürk, B., Bat, L., Oral, M., Mgeladze, M. (2014). Marine fishes in the Black Sea: recent conservation status. Mediterranean Marine Science,15/2, 366-379. Available at:

Rationale uncertainty

In the absence of data on both trends and impacts of invasive alien species in European Seas, trends in marine alien species (i.e. all introduced species that have the potential to become invasive) are used as a proxy of the trends of the most invasive marine alien species.

Climate change is proved to enhance the establishment of alien species (see Raitsos et al, 2010). Consequently, the presented analysis skews the real magnitude of the phenomenon since it focuses on non-indigenous species directly introduced by human activities.



Raitsos, D. E., Beaugrand, G., Georgopoulos, D., Zenetos, A., Pancucci-Papadopoulou, A. M., Theocharis, A., & Papathanassiou, E. (2010). Global climate change amplifies the entry of tropical species into the Eastern Mediterranean Sea.Limnology and Oceanography,55(4), 1478-1484. Available at:

Further work

Short term work

Work specified here requires to be completed within 1 year from now.

Long term work

Work specified here will require more than 1 year (from now) to be completed.

General metadata

Responsibility and ownership

EEA Contact Info

Stéphane ISOARD


European Environment Agency (EEA)


Indicator code
MAR 002
Version id: 1

Frequency of updates

Updates are scheduled every 3 years


DPSIR: Pressure
Typology: Descriptive indicator (Type A - What is happening to the environment and to humans?)


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