Pathways of introduction of marine non-indigenous species
Justification for indicator selection
Biological invasions are widely recognized as one of the main threats to biodiversity next to habitat destruction. 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 introduction of NIS and further spread of those that are invasive.
Knowledge of the invasion process of marine non-indigenous species is essential for designing adequate management plans and to attempt preventing the large-scale spread of IAS. Marine non-indigenous species may arrive and enter a new region mainly through three broad mechanisms: importation of a commodity, arrival in a transport vector and/or natural spread from a neighboring region where the species is itself alien. These are then further related to pathways, which describe the processes of introduction of a species from a location to another. Analyses of management actions against these pathways of introduction and number of alien species introduced over time may help prioritize responses.
In the absence of data on trends of invasive alien species in European seas, trends in marine NIS (i.e. all introduced species which have the potential to become invasive) is used as a proxy.
- No rationale references available
This indicator shows trends of marine non-indigenous species per pathway of introduction recorded in European seas since 1950. Analysis is shown at both European and regional sea level.
Number of non-indigenous species
Policy context and targets
The EU Biodiversity Strategy (EU, 2011) specifically stresses the need to assess pathways of biological invasions through its Target 5: "By 2020, invasive alien species and their pathways are identified and prioritized, priority species are controlled or eradicated, and pathways are managed to prevent the introduction and establishment of new invasive alien species".
The recently adopted European Commission Regulation on the prevention and management of the introduction and spread of invasive alien determines that Member States carry out a comprehensive analysis of the pathways of unintentional introduction and spread of invasive alien species of Union concern, at least, in their territory, as well as in their marine waters as defined in Article 3(1) of Directive 2008/56/EC, and identify the pathways which require priority action ('priority pathways'), because of the volume of species or of the potential damage caused by the species entering the Union through them. They will also need to establish and implement action plans to address the priority pathways identified within three years of the initial assessment.
Other international agreements cover different groups of MAS or pathways of their introduction and start to address MAS as a threat to biodiversity:
1. It has been recognized that aquaculture and related activities (e.g. sport fishing, fishery stock enhancement, ornamental trade) have been important drivers of alien species in Europe in the past and that the trade in alien species needs specific rules in order to prevent target and non-target species introduction into the wild. In 2007 the first EC regulation on alien species was approved: No 708 on 11 June 2007 (implemented rules: No. 535 on 13 June 2008) concerning the use of alien and locally absent species in aquaculture.
2. The International Maritime Organisation (IMO) adopted the "International Convention for the Control and Management of Ships' Ballast Water and Sediments". The aim of the Convention is to prevent, minimize and ultimately eliminate the transfer of harmful aquatic organisms and pathogens through the control and management of ships' ballast water and sediments.
3. The Convention for the Control and Management of Ship’s Ballast Water and Sediments under the International Maritime Organisation addresses ballast water as the main pathway for MAS.
4. The Convention on International Trade in Endangered Species of Wild Flora and Fauna (CITES) adopted a resolution on IAS during COP13 (and reviewed at COP14) (resolution 13.10, trade in alien invasive species).
Related policy documents
AFS, 2001. International Convention on the Control of Harmful Anti-Fouling Systems on Ships.
International Maritime Organization, London. 2001.
COM(2008) 789 Final
Communication from the Commission to the Council, the European Parliament, the European Economic and Social Committee and the Committee of the Regions Towards an EU Strategy on Invasive Species [SEC(2008) 2887 Et SEC(2008) 2886
Council of Europe (2003). European strategy on invasive alien species. Convention on the Conservation of European Wildlife and Natural Habitats (Bern Convention).
Council of Europe, T-PVS (2003) 7 revised: 60 pp.
Decision VI/23 on Alien Species that threaten ecosystems, habitats and species.
(COPVI, The Hague, April 2002) to which are annexed the Guiding Principles for the Prevention, Introduction and Mitigation of Impacts of Alien Species that threaten Ecosystems, Habitats or Species.
European Commission (2006). Proposal for a Council Regulation concerning use of alien and locally absent species in aquaculture.
COM(2006) 154 final: 32 pp.
European Commission (2013). Regulation Of The European Parliament And Of The Council on the prevention and management of the introduction and spread of invasive alien species.
COM(2013) 620 final 9.9.13, 46pp
IMO (1997). International Maritime Organisation, Guidelines for the Control and Management of Ships’ Ballast Water to Minimise the Transfer of Harmful Aquatic Organisms and Pathogens.
IMO Resolution A.868 (29). IMO, London.
IMO (2004). International Convention for the Control and Management of Ships’ Ballast Water and Sediments.
Methodology for indicator calculation
The list of species used is the same as that considered for the trends in introduction analysis (MAR002) and stored in HCMR/EEA data base. It includes both alien and cryptogenic species. The information on the country, year of first introduction of each species and pathway (s) is publicly available through the species search widgets of EASIN updated as of October 2013 (http://easin.jrc.ec.europa.eu/use-easin/species-search) and is also provided in the supplementary file of Nunes et al. (2014) http://www.aquaticinvasions.net/2014/Supplements/AI_2014_Nunes_etal_Supplement.xls. The HCMR/EEA data base is in full agreement with the classification given in EASIN, yet updated to June 2014.
Trends in introduction per pathway was calculated on a decadal basis, considering the very first sighting/collection of the species in European Waters. In the absence of exact collection date the date of publication was used as the best available information. All species, established plus casual were taken into account.
The primary pathway/vector was filled in to the degree possible. Marine and estuarine species are those aquatic species which do not complete their entire life cycle in freshwater (modified after ICES, 2005). Vagrant species, mostly fish and crustaceans of tropical Atlantic origin, whose mode of introduction is unknown, were not considered in our calculations. Thus, the pathway was calculated for 1416 species.
To categorize pathways of primary introduction of alien species into a new region, we have followed the framework proposed by Katsanevakis et al (2013).
Five pathways are associated with human activity either as commodities (release and escape), contaminants of commodities, stowaways on modes of transport and opportunists exploiting corridors resulting from transport infrastructures. The sixth category highlights alien species that may arrive unaided in a region as a result of natural spread (rather than human transport) following a primary human-mediated introduction in a neighbouring region.
Aquaculture: Historically, aquaculture and stock transfers of aquatic species resulted in a significant amount of taxa being transported worldwide. Of the species imported for mariculture, it is not known how many have been intentionally released for stocking. This is a practice for introduced species in inland waters not considered in this analysis. So, this category is not analysed here. However, we have included under the category ‘aquaculture escape’ those imported species that have escaped from aquaculture and spread in the wild, even if they are released freshwater species if found in estuarine areas of the Baltic Sea. The so called aquaculture contaminants is hereby assigned as ‘aquaculture accidentally introduced’ species.
Shipping: With regard to NIS, stowaways include organisms that foul the hulls of ships, are transported as seeds or resting stages in ballast water, as well as in shipping containers, cargo. Estimations reveal that more than 480,000 annual ship movements occur worldwide with the potential for transporting organisms. Various calculations have been made on the amount of ballast water carried with the world’s fleet of merchant ships – it has been estimated that 2–12 billion t of ballast water are transported annually. In ballast tanks and also other ship vectors including hulls, anchor chains and sea chests, ships may carry 4,000 to 7,000 taxa each day (Gollasch, 1996). Under shipping we have also included species transferred with recreational boats, mostly encountered in marinas, and species transferred with fishing boats.
Given the IMO Policies on Ballasts after 2004 (BWC), it was deemed important to examine the trends in the two different modes of introduction (ballasts and fouling) separately.
Under Corridors, we have separated those species progressively introduced via the Suez Canal (mostly Indo-Pacific species occurring in the eastern Mediterranean, called also Lessepsian immigrants) and those Ponto-Caspian species spreading in the Baltic via inland canals.
A final category is aquarium trade. The recent focus on the aquarium trade as a possible mechanism for environmentally sustainable development poses an especially dangerous threat (Papavlassopoulou et al, 2014), although this has so far escaped the attention of most environmentalists, conservationists, ecologists, and policy makers.
On investigating gateways of introduction in European Seas, the country and year of initial introduction of marine alien species in Europe was identified (for 1380 species in Nunes et al 2014). The country through which a species was first introduced in Europe will hereafter be called ‘recipient country’. For 31 species, more than one recipient country was associated to their introduction into European Seas. This may happen when a species has been collected independently at the same year from different countries, such as for example Desdemona ornata (Banse, 1957) from Italy (Lardicci and Castelli 1986) and Greece (Panagopoulos and Nicolaidou 1989-90),Fibrocapsa japonica (Toriumi and Takano, 1973) from France (Billard 1992) and Germany (Elbrächter 1994) or Hemigrapsus sanguineus (De Haan, 1835) from France and the Netherlands (Breton et al. 2002).
Given a potential multiple way of introduction at Pan European level, percentages add to more than 100% (i.e. 116.3%) as some species are linked to more than one pathway). Temporal trends in the numbers of new recorded marine aliens in Europe in relation to the pathways of introduction. Some species that were linked to more than one pathways were given a value of 1/k for each of the k associated pathways so that the overall contribution of each species to the total number of new aliens per decade was always 1 (Katsanevakis et al, 2013).
Methodology for gap filling
Unless found when deliberately moved, evidence of actual transmission is seldom known.
Information on vectors are mostly derived from expert judgement on an extensive review of the referred databases, since specific research projects aimed at identifying vectors and occurrences are complicated and demanding large resources. The only exception is published reports issued on maritime traffic worldwide (BWM, 2005). In a large number of cases, likely pathways are merely inferred, for example taking into account the most common activity occurring in a specific location (shipping, aquaculture), but no scientific evidence is provided.
Vertebrate pathways tend to be characterized as deliberate releases, exempting the Lessepsian immigrants that arrived unintentionally via the Suez Canal, invertebrates were introduced mostly as contaminants and plants as escapees. Pathogenic micro-organisms and fungi are generally introduced as contaminants of their hosts.
No methodology references available.
EEA data references
- No datasets have been specified here.
External data references
- MAMIAS - Marine Mediterranean Invasive Alien Species
- NOBANIS - European Network on Invasive Alien Species
- ICES/ WGITMO :Working Group on Introduction and transfers of Marine Organisms
- HCMR DataBase (not online)
- ELNAIS - invasive alien species data
- BSASD - Baltic Sea Alien Species Database
- AquaNIS, 2013. Information system on Aquatic Non-Indigenous species.
- EASIN: European Alien Species Information Network
- DAISIE - Delivering Alien Invasive Species Inventories for Europe
- GISD - Global Invasive Species Database
- GISIN - Global Invasive Species Information Network
- EPPO lists and documentation on invasive alien plants
- ICES/ WGBOSV:Working Group on Ballast and Other Ship Vectors
- REABIC - Regional Euro-Asian Biological Invasions Centre
Data sources in latest figures
In many cases, it is impossible to identify the introduction vector. Thus the pathway of 100 species is assigned as ‘unknown’. In bivalves, for example, introductions may be attributed to larval transport in ballast water releases, adults in hull fouling of ships or imports of stock for aquaculture purposes, or for direct human consumption but released into the environment
For species that are most frequently associated with hull fouling, this form of transport was assumed to be the responsible vector. For planktonic taxa and microscopic resting stages we have deemed ballast water to be the most likely vector since such species that are associated with hull fouling might be expected to become flushed away during ship journeys at sea. The human activities near to the site of the first records generally are assumed to be responsible for an introduction event. However, such deductions are not always secure and for this reason we have calculated more than one vector where the likely vector remains unclear. Forty species of tropical Atlantic origin have entered recently the Mediterranean via Gibraltar. These are classified as ‘vagrant’ and ‘range expansion’ and are not included in the pathway analysis.
Where more than one pathway of introduction is suspected/documented , the analysis has considered both modes of introduction. Thus the resulting percentage of contribution per pathway amounts to more than 100 %.
Data sets uncertainty
See rationale uncertainty
Different levels of certainty are associated with alien species that become introduced. A scheme proposed by Dan Minchin (2007), provides a basis for an improved quality of information for pathways and vectors.
(1) There is direct information of a pathway/vector: The species was clearly associated to a specific vector(s) of a pathway at the time of introduction to a particular locality. This is the case in intentional introductions (i.e. aquaculture/commodity) and in many cases of Lessepsian immigrants (when there was direct evidence of a gradual expansion along the Suez Canal and then in the localities around the exit of the Canal in the Mediterranean).
(2) Amost likely pathway/vector can be inferred: The species appears for the first time in a locality where a single pathway/vector(s) is known to operate and there is no other rational explanation for its presence except by this pathway/vector(s). This applies to many species introduced by shipping or aquarium trade or as aquaculture contaminants. In some cases a specific vector could not be inferred, e.g. some species probably introduced by shipping could not be further linked to ballasts or hull fouling and were classified as ‘shipping/unknown’. In many cases inference is based on known examples of introductions elsewhere for the same or similar species,the biology and ecology of the species, the habitats and locales it occupies in both the native and introduced range, and its pattern of dispersal (if known), e.g. for a fouling species frequently recorded in ports, shipping has been assumed to be the most probable vector.
(3) One or more possible pathways/vectors can be inferred: The species cannot be convincingly ascribed to a single pathway/vector. Inference is based on the activities in the locality where the species was found and may include evidence on similarly behaving species reported elsewhere.
(4) Unknown: Where there is doubt as to any specific pathway explaining an arrival. Herein, the pathway of 100 species has been assigned as ´unknown´.
Gruet, Y., Heral, M., Robert, J.-M., 1976. Premie`res observations sur l’introduction de la faune associe΄e au naissain d’huı tres Japonaises Crassostrea gigas (Thunberg), importe΄ sur la coˆ te Atlantique FrancΈaise. Cahiers de Biologie Marine 17, 173–184.
Hare, J.A., Whitfield, P.E., 2003. An integrated assessment of the introduction of lionfish (Pterois volitans/miles complex) to the Western Atlantic Ocean. NOAA Technical memorandum NOS NCCOS 2, 21
McMahon, R.F., 1983. Ecology of an invasive pest bivalve, Corbicula. In: The Mollusca, Vol. 6. Academic Press, pp. 505–553.
Minchin D., 2007. Aquaculture and transport in a changing environment: Overlap and links in the spread of alien biota. Marine Pollution Bulletin 55 (2007) 302–313
Lilly, E.L., Kulis, D.M., Gentien, P. & Anderson, D.M. (2002) Paralytic shellfish poisoning toxins in France linked to human-induced strain of Alexandrium catanella from the western Pacific: evidence from DNA and toxin analysis. Journal of Plankton Research, 24, 443–452.
Ruiz, G.M. & Carlton, J.T. (2003) Invasive Species: Vectors and Management Strategies. Island Press, Washington, DC.
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.
Responsibility and ownership
EEA Contact InfoConstança De Carvalho Belchior
Frequency of updates
Typology: Policy-effectiveness indicator (Type D)
For references, please go to www.eea.europa.eu/soer or scan the QR code.
This briefing is part of the EEA's report The European Environment - State and Outlook 2015. The EEA is an official agency of the EU, tasked with providing information on Europe’s environment.
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