The European Alien Species Information Network on the Convention on Biological Diversity pathways categorization

The adoption of a consistent alien species pathways categorization, hierarchy and terminology is crucial for increasing the interoperability of different online databases. In the present paper the European Alien Species Information Network (EASIN) classification system of pathways is compared and discussed with the classification scheme recently published by the Convention on Biological Diversity (CBD). Although the main pathway categories of the two classifications overall match, there are substantial differences in their subcategorization, with EASIN including 20 pathway subcategories while CBD considers 44 subcategories. In most cases, each EASIN subcategory pathway can correspond to two or more CBD subcategories. About 5,500 species listed in EASIN do not match directly with the CBD pathway subcategories, most of which are terrestrial invertebrates. Aiming at achieving synchronization between the two classification systems and at facilitating the access to information to researchers and policy makers, EASIN is trying to align with the CBD pathway classification scheme. This alignment process requires the involvement of a large number of experts, especially from the terrestrial realm, and the adoption of commonly accepted definitions of the CBD pathways.

Invasive Alien Species (IAS) constitute one of the most important threats to biodiversity, causing severe ecological and socio-economic impacts (Ricciardi et al. 2013, Jeschke et al. 2014).A conservative estimate of the annual damage caused in the European Union (EU) by IAS is €12 billion (Kettunen et al. 2009).In addition, there is an increasing trend of new alien introductions (Essl et al. 2015, Roques et al. 2016).Aiming at protecting European biodiversity, the European Parliament and the Council adopted the EU Regulation no.1143/2014 (EU 2014; hereafter referred to as the IAS Regulation) on the prevention and management of the introduction and spread of IAS, which entered into force on the 1 st of January 2015, and a list of 37 invasive alien species of Union concern, by means of Implementing Regulation 1141/2016.
The European Alien Species Information Network (EASIN, http://easin.jrc.ec.europa.eu/)has been developed by the European Commission's Joint Research Centre (JRC) (Katsanevakis et al. 2012), and formally recognized as the information system supporting European Member States in the implementation of the IAS Regulation (EU 2014, Art. 25).EASIN aims at allowing easier access to data of alien species occurring in Europe, and to provide a one-stop shop to access all the information necessary to underpin alien species related policy and management decisions (Katsanevakis et al. 2013).
Information on alien species introduction pathways is fundamental for the reliability and effectiveness of alien species risk assessments, management, monitoring, and surveillance (EU 2011, Ojaveer et al. 2014, McGeosh et al. 2016).Pathways categorization is an essential aspect, and can benefit from applying consistent pathways classification, hierarchy, and terminology (Essl et al. 2015).To aid these efforts, a standardized pathways terminology and hierarchical classification has been proposed by Hulme et al. (2008) and largely adopted by EASIN in 2012 (Katsanevakis et al. 2012).Since then, EASIN datasets have been used for pan-European or regional assessments of pathways of alien species invasions, towards the fulfilment of the related targets of the Convention on Biological Diversity (CBD) and of European policies (Katsanevakis et al. 2015).
The increasing threat of IAS has lead CBD to a comprehensive review of the alien species pathways, adopting a note of the executive Secretary on the categorisation of identified pathways of introduction of IAS (CBD 2014), addressing the needs of Aichi Biodiversity Target 9 concerning the identification, prioritization and management of IAS by 2020, which is reflected in Target 5 of the EU Biodiversity Strategy (EU 2011).The CBD pathway analysis was based on Hulme et al. (2008) study, and integrates a set of international standards and guidelines, aiming at harmonizing the existing large number of pathways described.CBD (2014) scope is to develop a categorization of pathways using standard terminology applicable at a global scale, facilitating the interoperability of different online databases.
In the present paper a comparative analysis between the EASIN and the CBD pathway classification schemes is presented (Table 1), highlighting the need for harmonization to allow data interoperability.Both systems exhibit very good match (83%) regarding their main-category pathways ("release in nature", "escape from confinement", "transport contaminant", "transport-stowaway", "corridor"), since they are Table 1.Comparison of sub-category pathways between CBD and EASIN classification systems; green colour corresponds to perfect match between the two systems; blue colour includes cases where an EASIN pathway corresponds to two (or more) CBD pathways; orange colour indicates a case where a CBD pathway corresponds to two EASIN pathways; red colour refers to cases where an EASIN pathway does not match with any CBD pathway or vice versa.The number of related species for each pathway in EASIN is also provided.2008) concept.The only mismatch observed concerns the "unaided" category, adopted by CBD.EASIN uses instead "other" as a category which includes the "unaided" pathway.On the other hand, substantial differences are observed in the subcategorization of pathways: EASIN includes 20 pathway subcategories, while the CBD includes 44 subcategories (Table 1), and thus offers more detailed information on species introduction channels.A perfect match is observed for 10 pathway subcategories between the two systems.More frequently, each EA-SIN subcategory corresponds to two or more CBD subcategories, or the opposite in one case, including 24 non-matching pathway subcategories considering both sides.A typical example is the EASIN "trade of contaminated commodities" pathway, assigned to about 3,400 species in EASIN, which could correspond to one or more among the ten related pathways of the CBD scheme (Table 1).Finally, there is no match at all concerning 14 subcategories included in both systems (Table 1).
A thorough comparison between the EASIN and CBD systems reveals that the sub-category pathways of about 5,500 alien species registered in EASIN (51% of the EASIN species with assigned pathway) do not match directly with the available CBD pathway subcategories.Similar comparisons were made by Essl et al. (2015) between the CBD scheme and GISD (Global Invasive Species Database), DAISIE (Delivering Alien Invasive Species Inventories for Europe) and GBNNSIP (Great Britain's Non-Native Species Information Portal) data, revealing higher levels of direct matching (from 79% to 99%).However, the number of species with assigned pathways in these databases is by far lower when compared with EASIN.
A more detailed analysis of the EASIN data reveals that 52% of the terrestrial alien species included in EASIN match with the CBD classification.In comparison, the matching between the two systems is higher for the freshwater species of EASIN (70%), but lower for the marine species (43%).Still, the corresponding number of the EASIN alien species per habitat is much higher for the terrestrial group compared to the marine and freshwater (Figure 1).When it comes to alien species of EASIN per main taxonomic group, a low match is observed for the invertebrates (28%, Figure 2); most of the mismatched species of EASIN are assigned to the pathway "trade of contaminated commodities" and "shipping" (Figure 3).On the other hand, there is a relatively good match for plants (66%), although given the size of the group, a considerable number of them do not match with the CBD pathways (Figure 2), most of them assigned to "trade of contaminated commodities" and "cultivation and livestock" (Figure 3).A good match is observed for vertebrates (80%), with a low number of mismatched species (Figure 2), most of which are related with 'game animals" and 'shipping" (Figure 3).When it comes to fungi and chromista, there is a very low match for both of them (1% and 22%, respectively), although their species number is by far lower compared to the other main taxonomic groups (Figure 2).Almost all mismatching fungi are assigned to "trade of contaminated commodities", while most mismatching chromista to "shipping" (Figure 3).It should be noted that the accurate determination of an alien species pathway is not always an easy task and it may be characterised by high levels of uncertainty (Katsanevakis et al. 2013).Therefore, higher level of detail in subcategorization will inevitably lead to further difficulties in pathways accurate determination.For example, it is known that most of the marine aliens in European seas have been introduced through shipping (Nunes et al. 2014), but the accurate assignment of their pathway in terms of CBD subcategories related to shipping ("hitchhikers on ship-boat excluding ballast water and hull fouling" / "ship-boat ballast water" / "ship-boat hull fouling") could offer a real challenge even to experts.On the other hand, higher level of pathways distinction could allow a better definition of legislative instruments or tailored measures preventing the entry of new aliens.
In addition, there are some points in the CBD scheme that need further clarification.For example, the distinction between the CBD sub-category pathways "horticulture" and "ornamental purpose other than horticulture" is not clear and could result in different interpretations among stakeholders.This is especially important for alien land plants, where about 2,000 species in EASIN are assigned to the "ornamental planting" pathway (Table 1).
Still, the need for interoperability among pathway classification systems is today crucial, considering also the recent IAS Regulation implementation needs.Pathway terminology has historically varied among alien species databases (Hulme et al. 2008), restricting comparisons across data repositories (CBD 2014).In order to tackle this, JRC is revising the EASIN pathway classification system and harmonise it with the CBD scheme, aiming at enhancing interoperability and facilitate exchange of information amongst databases on alien species, but also to support the analysis of pathways and their relative importance for prioritising management and to facilitate the development of response options to tackle IAS.
The alignment of the EASIN species to the CBD pathway sub-categories is challenging and resources demanding due to the high number of EASIN species that need to be revised.In some cases this can be relatively simple; i.e. species assigned to "game animals" correspond either to "fishery in the wild" or to "hunting" in terms of the CBD classification.However, for species related with other pathway subcategories (e.g.'trade of contaminated commodities") their alignment to the CBD system is more demanding and requires deep search in the scientific literature and any other relevant sources of information.Moreover, pathway assignment for less documented species is subject to uncertainty (Essl et al. 2015), setting the need for experts' judgement.Therefore, a large number of experts will be involved in the revision process of the EASIN pathways, covering a broad range of taxonomic groups and habitats.Emphasis should be given to the terrestrial species due to their large number, with the involvement of additional experts, especially when it comes to invertebrates (mostly insects), higher plants and fungi.In addition, uncertainty values attached to each pathway (Katsanevakis et al. 2013) will be included in the alignment process.Finally, it should be noted that the harmonization process of pathways requires a consensus from the scientific community on commonly accepted definitions and related interpretations of the CBD pathways, ensuring homogeneous alignment outcomes.

Figure 1 .
Figure 1.Pathway matching between EASIN and CBD sub-category classification systems for alien species included in EASIN per habitat.

Figure 3 .
Figure 3. Number of EASIN alien species per main taxonomic group with assigned pathway not matching the CBD classification.The related number of alien species corresponding to each EASIN pathway is also depicted.

Figure 2 .
Figure 2. Pathway matching between EASIN and CBD sub-category classification systems for alien species included in EASIN per main taxonomic groups.