Frequently Asked Questions

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What are Non-indigenous species ?

Non-indigenous species (NIS; synonyms: alien, exotic, non-native, allochthonous) are species, subspecies, or lower taxa introduced outside of their natural range (past or present) and outside of their natural dispersal potential.


What are Invasive Non-indigenous species ?

Invasive alien species (IAS) are a subset of established NIS which have spread, are spreading, or have demonstrated their potential to spread elsewhere, and which have an effect on biological diversity and ecosystem functioning (by competing with and on some occasions replacing native species), socioeconomic values, and/or human health in invaded regions.


What is Common Indicator 6?

In the context of the Barcelona Convention, a common indicator is an indicator that summarizes data into a simple, standardized, and communicable figure and is ideally applicable in the whole Mediterranean basin, or at least on the level of sub-regions, and is monitored by all Contracting Parties. A common indicator is able to give an indication of the degree of threat or change in the marine ecosystem and can deliver valuable information to decision makers.


What is WoRMS?

The aim of a World Register of Marine Species (WoRMS) is to provide an authoritative and comprehensive list of names of marine organisms, including information on synonymy. While the highest priority goes to valid names, other names in use are included so that this register can serve as a guide to interpret taxonomic literature.

The content of WoRMS is controlled by taxonomic and thematic experts, not by database managers. WoRMS has an editorial management system where each taxonomic group is represented by an expert who has the authority over the content, and is responsible for controlling the quality of the information. Each of these main taxonomic editors can invite several specialists of smaller groups within their area of responsibility to join them.



Usage of data from WoRMS in scientific publications should be acknowledged by citing as follows:

MAMIAS (yyyy).MArine Mediterranean Invasive Alien Species Database. Available from Accessed Accessed dd-mm-yyyy. doi:10.14284/170

Pathways categorization is aligned to the one proposed by the Convention of the Biological Diversity (CBD, 2014).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 See Guidance for interpretation of CBD

Certainty is given following the criteria identified in Tsiamis et al. 2018,:

  • High: there is direct evidence of a pathway;
  • Medium: a likely pathway can be inferred; the NIS appears for the first time in a locality where a pathway is known to operate. This applies to many species introduced e.g. by shipping ballast (Transport – Stowaway: ship/boat ballast water) or as aquaculture contaminants (Transport – Contaminant: contaminant on animals – except parasites, species transported by host/vector).
  • Low: NIS cannot be convincingly ascribed to a single pathway; usually, two or more possible pathways can be inferred.

  • NIS: Species non-native to the ecosystem (introduced outside its natural distribution range);
  • Cryptogenic: Species with no definite evidence of their native or introduced status according to CARLTON (1996);
  • Debatable: species with an unresolved taxonomic status.

  • Established: a species with at least a selfmaintaining population currently known to occur in the wild.
  • Casual: a species whose only a single or few specimens have been recorded
  • Invasive: an established species that is spreading rapidly, with documented impacts on the ecosystem and its services
  • Questionable: species whose presence in the country is questionable and needs to be confirmed (re-examination of material if available).
  • Unknown: mainly for old records whose recent population status is not reported/published as well as for newly reported species.