Relevant Terminology

1. Definitions as referred to by PortShield
1.1. Alien Species

Source: As agreed by the Convention on Biological Diversity (CBD)
Definition: A species, subspecies or lower taxon (such as a variety, race, provenance or stock), introduced outside its natural past or present distribution; includes any part, gametes, seeds, eggs, or propagules of such species that might survive and subsequently reproduce (COP 6, decision VI/23)
Known synonyms: Non-Native Species, Non-Indigenous Species, Foreign Species, Exotic Species, Introduced Species

Based on the above then: Marine Alien Species

Definition: Alien species found in marine habitats.
Known synonyms: Marine Non-Native Species, Marine Non-Indigenous Species, Marine Foreign Species, Exotic Marine Species, Introduced Marine Species

1.2. Invasive Aquatic Species (IAS)

Source: As used by the International Maritime Organisation (IMO)
Definition: A species which may pose threats to human, animal and plant life, economic and cultural activities and the aquatic environment (MEPC 62/24/Add.1, Annex 26, page 4)

Known synonyms: Invasive Aquatic Alien Species, Invasive Non-Native Aquatic Species, Invasive Non-Indigenous Aquatic Species

Note: It should be noted that ‘aquatic’ habitats may include freshwater, marine, or brackish water. PortShield subscribes to the terminology adopted by the International Maritime Organsation for consistency purposes, however, it is recognised that the main types of species that may be translocated as a result of international shipping are marine fouling organisms.

2. The difference between alien species and invasive aquatic species (IAS)

2.1. Alien species and invasive species

It should be borne in mind that not all alien species are invasive but some might become invasive (International Union for Conservation of Nature, 2018 ). However, the potential impact on biodiversity and the economic impact of managing and eradication programmes can be severe.

The EU regulation on the prevention and management of the introduction and spread of invasive alien species (Regulation (EU) No 1143/2014 of the European Parliament and of the Council of 22 October 2014) states:

  1. ‘The appearance of alien species, whether of animals, plants, fungi or micro-organisms, in new locations is not always a cause for concern. However, a significant subset of alien species can become invasive and have serious adverse impact on biodiversity and related ecosystem services, as well as have other social and economic impact, which should be prevented. Some 12 000 species in the environment of the Union and in other European countries are alien, of which roughly 10 to 15 % are estimated to be invasive.
  2. Invasive alien species* represent one of the main threats to biodiversity and related ecosystem services, especially in geographically and evolutionarily isolated ecosystems, such as small islands. The risks such species pose may intensify due to increased global trade, transport, tourism and climate change.
  3. The threat to biodiversity and related ecosystem services that invasive alien species pose takes different forms, including severe impacts on native species and the structure and functioning of ecosystems through the alteration of habitats, predation, competition, the transmission of diseases, the replacement of native species throughout a significant proportion of range and through genetic effects by hybridisation. Furthermore, invasive alien species can also have a significant adverse impact on human health and the economy…’

Katsanevakis et al (2013) warn about the potential negative impact of marine alien species:

‘Marine alien species may become invasive and displace native species, cause the loss of native genotypes, modify habitats, change community structure, affect food-web properties and ecosystem processes, impede the provision of ecosystem services, impact human health, and cause substantial economic losses (Grosholz, 2002; Molnar et al., 2008; Vilà et al., 2010; Wallentinus and Nyberg, 2007).’

2.2. Invasive species – existing definitions

There are many existing definitions of ‘invasive species’. In some instances, ‘invasive species are simply defined as ‘any species reported to have become established outside of its native range’ (Molnar et al 2008). Such broader definitions are sometimes used in the literature especially in studies which aim to capture data on introductions (Molnar et al, 2008).

However, the definitions of ‘invasive species’ used for public policy purposes usually stipulate that for species to be regarded as ‘invasive’ they need to pose a threat and to have a potentially negative impact from an environmental, economic or public health perspective. For example, the definition used in the US Federal Executive Order 13112 (1999), which is similar to the one used by PortShield, states that invasive species are:

‘alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health’

Academic References:
Katsanevakis, S., Zenetos, A., Belchior, C., Cardoso, A. C. 2013. Invading European Seas: Assessing pathways of introduction of marine aliens. Ocean & Coastal Management, Volume 76: pp 64-74,

Molnar, J., Gamboa, R., Revenga, C., Spalding, M. 2008. Assessing the global threat of invasive species to marine biodiversity. Front Ecol Environ; 6(9): pp 485–492, doi:10.1890/070064

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