Frequently asked questions

No. Invasive alien species are “a subset of established NIS”: established, spreading or able to spread, and with a demonstrated effect. A species can be non-indigenous and casual, or established without any documented impact. MAMIAS records the NIS status and the establishment status separately (see section 02).

“Trends in abundance, temporal occurrence, and spatial distribution of non-indigenous species, particularly invasive, non-indigenous species, notably in risk areas”, in relation to the main vectors and pathways. IMAP treats it as “a trend monitoring, where it is key to establish reliable, standardized monitoring and long-term data-sets”. In practice its temporal trend is computed from the dates of first records, which is why backdating matters.

Not yet: “threshold values for the number of new introductions of non-indigenous species have not been set neither at the EU or the Mediterranean level.” The recommended approach is a percentage reduction of new NIS, decided per region or subregion. The Mediterranean analysis of 1970–2017 data found a significant rise in new NIS after 2000 that differs between EcAp subregions, so IMAP recommends:

• thresholds set at subregional level, not regional;
• only data after the 2000s used to set them;
• six-year assessment periods aligned with the MSFD, or three years where monitoring has been weak.

The assessment criteria decide which taxa (all, or without phytoplankton and parasites), which species (extinct, cryptogenic, crypto-expanding, questionable) and which pathways (all, or without unaided expanding species such as Lessepsian immigrants) enter the trend. “Partly native species, NIS introduced through natural dispersal, unicellular marine algae, parasites, extinct and freshwater species should be reported in NIS lists but considered in CI6 assessments on a case-by-case basis.” MAMIAS keeps them all, flagged, so each assessment can apply the criteria.

IMAP names it as a source for the national lists: “Based on existing regional databases, such as the Marine Mediterranean Invasive Alien Species database, (MAMIAS), […] each Contracting Party should update the list of IAS to be monitored in its national monitoring programme at the start of each new phase of IMAP” (Annex II, para. 66). MAMIAS also holds the regional baseline (UNEP/MED WG.521/Inf.8): validated records to the end of 2020, 1,011 NIS of which 748 established.

Galanidi et al. (2023, p. 13) accept a species when “(a) at least one record has been sufficiently documented (with detailed descriptions and/or illustrations); (b) and/or voucher specimen(s) are provided for inspection, which are deposited in a museum collection; (c) and/or genetic data have confirmed the record where ambiguities from morphological identification have arisen”.

• Records based on non-living animals, mostly mollusc shells.
• Species reported only from vectors, such as polychaetes and bryozoans found only on ship hulls.
• Unicellular plankton, as a rule, “because the origin of most species is in doubt”; parasites are included.

Either national experts could not agree whether it is alien or cryptogenic, or its taxonomy is unresolved (species complexes, suspected undescribed native species), or its record is questionable: “species records with insufficient information (e.g., no voucher or description provided), or with uncertain identification”. Data deficient species are kept apart until their status is settled.

A species that reaches the Mediterranean by its own means has not been introduced, so it falls outside the definition of a NIS. “Range-expanding and partly native (i.e., native in one country/subregion but introduced in another) species in the Mediterranean were excluded at Pan-Mediterranean scale. However, species partly native in a subregion were included at the subregional scale.”

They are two publications of the same validation work, both covering records to the end of 2020: the paper counts 1,006 validated NIS, and the regional baseline cited in Decision IG.27/6 (UNEP/MED WG.521/Inf.8) counts 1,011. The group totals differ in the same small way (for example 222 and 224 Mollusca). MAMIAS keeps the baseline current as new records are validated.

The pathway is the route and purpose of the introduction (the CBD category and subcategory); the vector is what physically carries the species: “agents that transport the alien species such as trains, containers, ships etc.” (p. 336). A ship is the vector of both ballast water and hull fouling, which are two stowaway pathways.

“Where the alien species has a trophic or abiotic relationship to a specific substrate, meaning it cannot survive without it, it is clearly a Contaminant.” And: “if the contaminated substratum is itself a commodity and a vector, then the assigned pathway should fall in the Contaminant category. However, if the contaminated substratum is only a vector (physical or biological), then the assigned pathway should fall in the Stowaway category.” A parasite of imported oysters travels as a contaminant; an organism fouling a hull travels as a stowaway.

The primary pathway brings the species into the region; secondary pathways spread it within the region afterwards. In Pergl et al., primary covers “all independent introductions to Europe from regions of their native range and also from regions outside Europe where they are alien”; secondary covers “means of dispersal or transfer of species between country/regions where the species is non-native after introduction through the primary pathway(s)”. For most groups, secondary spread is mostly “Unaided /natural spread across borders”.

Their primary pathway is not assessed: “if we knew that they were introduced with a specific pathway, we would be certain of their alien status. For these species, it makes sense to assess only the secondary spread pathways” (p. 351).

• Floating marine litter: Transport – stowaway, other means of transport. Drifting is natural, but “the presence of anthropogenic marine litter is a human influence”.
• Bilge water: Transport – stowaway, other means of transport, not ballast water, “due to their different character and aspect of regulation”.
• By-catch discards: a relevant pathway of secondary spread, highest from bottom trawlers (e.g. Plotosus lineatus in the Mediterranean).
• Aquarium species: “most often intentionally dumped into the waters”, so Release, with a new subcategory for pet and aquarium species proposed. The escape of Caulerpa taxifolia from the Monaco aquarium is the paper's example of escape.

The NIS indicator for Good Environmental Status, under the MSFD and IMAP, “currently relies on species first record dates to calculate temporal trends in marine NIS introduction rates.” Moving a first record changes the period it counts in, and “increased backdating will lengthen reporting time lags […], alter temporal and spatial trends in NIS inventories, and may affect policy indices that only consider species introduced after 1970 for the calculation of time trends.”

• It never overwrites a first record silently: the year, country and reference replaced are kept in the event's first-record history, with the reason.
• A weekly check lists events that another record dates earlier: an approved occurrence, a country's or a subregion's first record, or EASIN's first EU record.
• Data corrections are kept apart, so backdating figures count only real backdates.

The paper's rule: when a species is reported only as present before a year (e.g. < 1970), that year is used; when no date is given at all, “the year of the publication was registered as the year of the species record.” MAMIAS records which of the three a year is (exact collection year, before this year, or publication year), and only an exact year counts toward the reporting time lag.

The authors expect so: “It is expected that the number of backdated NIS will increase once several overlooked specimens stored in drawers or museum collections are re-examined and /or new techniques are applied”, including DNA from formalin-preserved specimens. Backdating intervals grew with the date of the original record up to about 1970 and have shortened since, a sign of faster taxonomic work and its use in NIS management.