Corresponding author: Jan Pergl ( jan.pergl@ibot.cas.cz ) Academic editor: Tammy B. Robinson
© 2020 Jan Pergl, Giuseppe Brundu, Colin A. Harrower, Ana C. Cardoso, Piero Genovesi, Stelios Katsanevakis, Vanessa Lozano, Irena Perglová, Wolfgang Rabitsch, Gareth Richards, Alain Roques, Stephanie L. Rorke, Ricardo Scalera, Karsten Schönrogge, Alan Stewart, Elena Tricarico, Konstatinos Tsiamis, Andrea Vannini, Montserrat Vilà, Argyro Zenetos, Helen E. Roy.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Pergl J, Brundu G, Harrower CA, Cardoso AC, Genovesi P, Katsanevakis S, Lozano V, Perglová I, Rabitsch W, Richards G, Roques A, Rorke SL, Scalera R, Schönrogge K, Stewart A, Tricarico E, Tsiamis K, Vannini A, Vilà M, Zenetos A, Roy HE (2020) Applying the Convention on Biological Diversity Pathway Classification to alien species in Europe. In: Wilson JR, Bacher S, Daehler CC, Groom QJ, Kumschick S, Lockwood JL, Robinson TB, Zengeya TA, Richardson DM. NeoBiota 62: 333-363. https://doi.org/10.3897/neobiota.62.53796
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The number of alien species arriving within new regions has increased at unprecedented rates. Managing the pathways through which alien species arrive and spread is important to reduce the threat of biological invasions. Harmonising information on pathways across individual sectors and user groups is therefore critical to underpin policy and action. The European Alien Species Information Network (EASIN) has been developed to easily facilitate open access to data of alien species in Europe. The Convention on Biological Diversity (CBD) Pathway Classification framework has become a global standard for the classification of pathways. We followed a structured approach to assign pathway information within EASIN for a subset of alien species in Europe, which covered 4169 species, spanning taxonomic groups and environments. We document constraints and challenges associated with implementing the CBD Pathway Classification framework and propose potential amendments to increase clarity. This study is unique in the scope of taxonomic coverage and also in the inclusion of primary (independent introductions to Europe) and secondary (means of dispersal for species expansion within Europe, after their initial introduction) modes of introduction. In addition, we summarise the patterns of introduction pathways within this subset of alien species within the context of Europe.
Based on the analyses, we confirm that the CBD Pathway Classification framework offers a robust, hierarchical system suitable for the classification of alien species introduction and spread across a wide range of taxonomic groups and environments. However, simple modifications could improve interpretation of the pathway categories ensuring consistent application across databases and information systems at local, national, regional, continental and global scales. Improving consistency would also help in the development of pathway action plans, as required by EU legislation.
accidental introduction, alien species, deliberate introduction, pathways, secondary spread
Over the last decade, there has been considerable improvement in understanding macro-ecological determinants of biological invasions (
It has been repeatedly suggested that one of the most effective strategies to prevent new introductions of invasive alien species (IAS) and, hence, to limit future costs to society and protect biodiversity and ecosystems, is through the management of major (or “priority”) pathways and corresponding vectors (
Acknowledging the importance of assessing patterns in pathways where alien species arrive within new regions (primary introductions) or their spread following introduction (secondary spread), a standardised pathway terminology and hierarchical classification was proposed (Hulme et al. 2008). This framework has been extensively used in various studies assessing variation in pathways of introduction across different environments, taxonomic groups and ecological impacts (
The DAISIE database, including the records of impact, pathways and associated references, was added to the European Alien Species Information Network (EASIN;
Successively, a new unified system to categorise introduction pathways of alien species was proposed by the CBD (2014) through the document UNEP/CBD/SBSTTA/18/9/Add.1 to improve the understanding of the most relevant vectors (agents that transport the alien species such as trains, containers, ships etc.) and activities of introduction of alien species. The CBD Pathway Classification framework has since become a standard for pathway terminology, which is a key requirement for interoperability and harmonisation of databases (
A number of pathways associated with the introduction of alien species have been well-documented. These include the ornamental horticultural trade (
The EU IAS regulation requires EU Member States to carry out a comprehensive analysis and prioritisation of the pathways of unintentional introduction and spread of invasive alien species of Union concern. This is based on the number or volume of species or the potential adverse impact caused. A description of the active pathways of introduction and spread, including where relevant vectors and commodities with which the species is generally associated, is also required for risk assessments according to the EU IAS regulation (
In this paper, we discuss issues arising from the implementation of the CBD Pathway Classification framework, based on an expert assessment within the EASIN database, to assigning pathway information for a large subset of alien species in Europe. We summarise the patterns and trends amongst the taxon groups in this dataset, which is based on the experience gained through the process. We also discuss the potential amendments which may be required to the CBD Pathway Classification framework to improve consistency in its application. We are aware that the set of taxa is not exhaustive and does not randomly cover the full alien species pool in Europe; however, no comparable dataset is currently available that uses the primary and secondary pathways in the detailed CBD Pathway Classification framework. Therefore, this study can be considered as the first and only experience available globally and carried out on a large scale to align the pathway information of a regional database with the proposed CBD Pathway Classification framework.
The study was based on review and classification of pathways for alien species in Europe as part of a study funded by the European Commission to populate the EASIN catalogue. The EASIN catalogue was established by the EU, but it covers the whole area of Europe (https://easin.jrc.ec.europa.eu/easin/Catalogue). Pathways, based on Hulme et al. (2008), were initially assigned by the Joint Research Centre (JRC) of the European Commission for selected species covering a range of taxonomic groups and environments. A proportion of the above pathways (catalogue version from 2017) did not directly map on to a single pathway within the CBD Pathway Classification framework (see comparison of CBD and EASIN subcategory comparison in
Number of alien species included in the study (see Suppl. material
Taxonomic/environmental groups | No. of assessed taxa | EASIN species |
Algae | 129 | 150 |
Microorganisms | 567 | 900 |
Marine and Freshwater invertebrates | 718 | 2300 |
Nematodes | 39 | 170 |
Plants | 434 | 6600 |
Terrestrial invertebrates | 2102 | 3400 |
Vertebrates | 180 | 700 |
For each species, 3–4 experts with knowledge of the specific taxonomic/environmental groups were selected. Each expert was assigned a subset of alien species and performed searches of the scientific literature (WoS), online repositories of information on alien species (e.g. CABI Invasive Species Compendium, CABI abstracts, DAISIE database, EPPO Global Database) and grey-literature to find information on primary introduction and secondary spread pathways. For each assessed alien species, these pathways were then assigned to one or more of the CBD pathways categories and subcategories and at least one supporting reference was given for each recorded pathway. This was based on the CBD Pathway Classification guidance document that was developed during the same period (
As many alien species spread within or between neighbouring regions through secondary pathways, which often differ from the primary ones, each assessor had to distinguish between the primary and secondary pathway(s). Primary pathways in this study covered all independent introductions to Europe from regions of their native range and also from regions outside Europe where they are alien. Secondary pathways cover means of dispersal or transfer of species between country/regions where the species is non-native after introduction through the primary pathway(s) (i.e. from a European country/region where the species is alien to another European country/region where it is also alien, but was not previously present). The primary pathways were not applied to species with both a native and alien range within Europe (alien in) because the assignment of pathways was at the European scale.
In addition to the pathway assignments, experts were asked to provide a measure of their confidence (i.e. low, intermediate or high) for each pathway assigned to an alien species. To determine the confidence related to a given pathway assignment, several aspects were considered. Two of the most important aspects were the quality of the source in which the pathway information was found and the quality and appropriateness of the evidence itself (see Fig.
The pathways and associated confidence level assigned by an expert were subsequently reviewed by another expert from the same taxonomic/environmental group within the project team. For each pathway assignment, the reviewer could either agree with the initial expert or disagree with the assigned pathway and/or its confidence level. Reviewers were also asked to provide any comments and/or justification related to their decision. In addition to agreeing or disagreeing with the assignments made by the initial expert, the reviewers were also invited to assign new additional primary or secondary pathways for the species, if any. The final assignment to pathways and confidence levels were then reviewed by additional experts from the same taxonomic/environmental group.
We were not able to provide any pathway information for 327 fungi and pathogens, 51 terrestrial arthropods, eight aquatic invertebrates (marine and freshwater) and one plant (Carduus nutans), because of a lack of available evidence. Therefore, the final list of species with at least one pathway was 3782. In total, the assignment of pathway information resulted in 7658 taxon/pathway combinations, supported by 2288 references (i.e. unique articles, web pages, reports). With the exception of plants and terrestrial arthropods, the number of identified secondary pathways was lower than that of primary introductions, with the greatest relative difference observed for vertebrates (Table
Number of alien species within each broad taxonomic/environmental group assigned to introduction (primary pathway) and spread (secondary pathway).
Taxonomic/environmental groups | Primary introduction | Secondary spread |
Algae | 126 | 36 |
Microorganisms | 221 | 100 |
Marine and Freshwater invertebrates | 620 | 207 |
Nematodes | 29 | 19 |
Plants | 298 | 303 |
Terrestrial invertebrates | 1345 | 1499 |
Vertebrates | 177 | 15 |
Table
(part 1) Percentages within the broad taxonomic/environmental groups and numbers (in brackets) of records per taxon/pathway combinations and CBD Pathway Classification subcategories. Data are shown separately for introduction (primary pathway) and spread (secondary pathway).
Pathway type (Hulme et al. 2008) | Release in nature | Escape from confinement | |||||||||||||||||||||||
CBD Pathway Classification category | Biological control | Erosion control/ dune stabilization (windbreaks, hedges, …) | Landscape/flora/fauna “improvement” in the wild | Fishery in the wild (including game fishing) | Hunting | Introduction for conservation purposes or wildlife management | Release in nature for use (other than above, e.g., fur, transport, medical use) | Other intentional release | Agriculture (including Biofuel feedstocks) | Farmed animals (including animals left under limited control) | Forestry (including afforestation or reforestation) | Fur farms | Aquaculture / mariculture | Botanical garden/zoo/aquaria (excluding domestic aquaria) | Pet/aquarium/terrarium species (including live food for such species) | Horticulture | Ornamental purpose other than horticulture | Research and ex-situ breeding (in facilities) | Live food and live bait | Other escape from confinement | |||||
Primary introduction | Algae | 0.8 (1) | 2.3 (3) | ||||||||||||||||||||||
Microorganisms | |||||||||||||||||||||||||
Marine and Freshwater invertebrates | 0.7 (5) | 0.1 (1) | 1.1 (8) | 1.1 (8) | 0.3 (2) | ||||||||||||||||||||
Nematodes | |||||||||||||||||||||||||
Plants | 6.5 (28) | 2.8 (12) | 1.2 (5) | 2.3 (10) | 8.1 (35) | 4.6 (20) | 0.7 (3) | 6.2 (27) | 6 (26) | 10.9 (47) | 46.4 (201) | 0.5 (2) | |||||||||||||
Terrestrial invertebrates | 0.2 (4) | 0.1 (2) | 0.2 (4) | 0.5 (11) | 0.2 (5) | 0 (1) | |||||||||||||||||||
Vertebrates | 2.8 (5) | 2.2 (4) | 23.3 (42) | 22.2 (40) | 3.3 (6) | 1.1 (2) | 28.3 (51) | 0.6 (1) | 2.2 (4) | 10 (18) | 2.8 (5) | 11.1 (20) | 0.6 (1) | 7.2 (13) | |||||||||||
Secondary spread | Algae | 0.8 (1) | |||||||||||||||||||||||
Microorganisms | 0.4 (1) | ||||||||||||||||||||||||
Marine and Freshwater invertebrates | 0.1 (1) | 0.3 (2) | 0.7 (5) | 0.6 (4) | 0.1 (1) | ||||||||||||||||||||
Nematodes | |||||||||||||||||||||||||
Plants | 7.6 (33) | 2.5 (11) | 1.8 (8) | 1.8 (8) | 7.2 (31) | 3 (13) | 0.7 (3) | 5.3 (23) | 3.5 (15) | 9.7 (42) | 13.6 (59) | 0.5 (2) | 1.6 (7) | ||||||||||||
Terrestrial invertebrates | 0.2 (4) | 0.2 (5) | |||||||||||||||||||||||
Vertebrates | 0.6 (1) | ||||||||||||||||||||||||
Pathway type (Hulme et al. 2008) | Transport- contaminant | Transport- stowaway | Corridor | Unaided | |||||||||||||||||||||
CBD Pathway Classification category | Contaminant nursery material | Contaminated bait | Food contaminant (including of live food) | Contaminant on animals (except parasites, species transported by host/vector) | Parasites on animals (including species transported by host and vector) | Contaminant on plants (except parasites, species transported by host/vector) | Parasites on plants (including species transported by host and vector) | Seed contaminant | Timber trade | Transportation of habitat material (soil, vegetation,…) | Angling/fishing equipment | Container/bulk | Hitchhikers in or on airplane | Hitchhikers on ship/boat (excluding ballast water and hull fouling) | Ship/boat ballast water | Ship/boat hull fouling | Machinery/equipment | People and their luggage/equipment (in particular tourism) | Organic packing material, in particular wood packaging | Vehicles (car, train, …) | Other means of transport | Interconnected waterways/basins/seas | Tunnels and land bridges | Natural dispersal across borders of invasive alien species that have been introduced through pathways 1 to 5 | |
Primary introduction | Algae | 51.2 (66) | 1.6 (2) | 0.8 (1) | 32.6 (42) | 53.5 (69) | 0.8 (1) | 17.8 (23) | |||||||||||||||||
Microorganisms | 72.5 (174) | 3.8 (9) | 7.1 (17) | 18.3 (44) | 24.6 (59) | 25.8 (62) | 5.4 (13) | 20.8 (50) | 2.1 (5) | 2.5 (6) | 2.5 (6) | 0.8 (2) | 1.7 (4) | 1.3 (3) | |||||||||||
Marine and Freshwater invertebrates | 12.7 (90) | 5.6 (40) | 1.3 (9) | 2.5 (18) | 0.3 (2) | 0.1 (1) | 53.7 (381) | 48 (341) | 0.1 (1) | 2.4 (17) | 15.9 (113) | 0.1 (1) | |||||||||||||
Nematodes | 30.8 (12) | 2.6 (1) | 30.8 (12) | 10.3 (4) | 46.2 (18) | 10.3 (4) | 5.1 (2) | 30.8 (12) | 5.1 (2) | 10.3 (4) | 17.9 (7) | 7.7 (3) | 10.3 (4) | ||||||||||||
Plants | 0.9 (4) | 0.9 (4) | 2.3 (10) | 0.2 (1) | 0.5 (2) | 0.5 (2) | 14.5 (63) | 0.9 (4) | 3.5 (15) | 0.2 (1) | 0.7 (3) | 1.8 (8) | 0.2 (1) | 0.9 (4) | 0.2 (1) | 0.9 (4) | 0.9 (4) | 0.9 (4) | 0.2 (1) | ||||||
Terrestrial invertebrates | 11.3 (232) | 11.8 (241) | 0.1 (2) | 3.5 (72) | 32.2 (660) | 0.9 (18) | 2 (42) | 2.8 (57) | 8.5 (175) | 2.9 (60) | 0.4 (8) | 4.4 (90) | 0 (1) | 0.3 (7) | 1.7 (34) | 0.9 (18) | 0.2 (4) | 0.1 (2) | |||||||
Vertebrates | 3.3 (6) | 0.6 (1) | 1.1 (2) | 1.1 (2) | 0.6 (1) | 0.6 (1) | 0.6 (1) | 17.8 (32) | 13.3 (24) | 1.1 (2) | 0.6 (1) | 0.6 (1) | 0.6 (1) | 5.6 (10) | |||||||||||
Secondary spread | Algae | 4.7 (6) | 7 (9) | 5.4 (7) | 15.5 (20) | 15.5 (20) | |||||||||||||||||||
Microorganisms | 10 (24) | 3.8 (9) | 0.4 (1) | 5 (12) | 2.9 (7) | 0.4 (1) | 0.4 (1) | 9.2 (22) | 1.7 (4) | 1.7 (4) | 1.3 (3) | 2.5 (6) | 20.8 (50) | ||||||||||||
Marine and Freshwater invertebrates | 0.1 (1) | 6.1 (43) | 4.8 (34) | 1.1 (8) | 0.3 (2) | 2 (14) | 1.4 (10) | 0.3 (2) | 12.4 (88) | 7.2 (51) | 2 (14) | 0.1 (1) | 0.4 (3) | 2.3 (16) | 5.9 (42) | ||||||||||
Nematodes | 15.4 (6) | 7.7 (3) | 30.8 (12) | 7.7 (3) | 7.7 (3) | 25.6 (10) | 5.1 (2) | 5.1 (2) | 5.1 (2) | 2.6 (1) | 5.1 (2) | 5.1 (2) | |||||||||||||
Plants | 2.3 (10) | 0.5 (2) | 6.2 (27) | 0.5 (2) | 2.1 (9) | 0.9 (4) | 21.5 (93) | 0.5 (2) | 13.4 (58) | 0.2 (1) | 2.8 (12) | 0.7 (3) | 20.1 (87) | 4.2 (18) | 0.9 (4) | 6 (26) | 3.2 (14) | 2.1 (9) | 0.2 (1) | 19.4 (84) | |||||
Terrestrial invertebrates | 10.3 (211) | 13 (267) | 0.1 (3) | 3.3 (68) | 35.7 (733) | 0.5 (11) | 2.9 (59) | 5.2 (107) | 10.4 (213) | 0.3 (7) | 0 (1) | 2 (41) | 0 (1) | 0.8 (17) | 2 (40) | 4.6 (95) | 0.1 (2) | 0 (1) | 2.6 (54) | ||||||
Vertebrates | 0.6 (1) | 1.1 (2) | 6.1 (11) |
There was variation in the frequency of CBD Pathway Classification (sub)categories relevant to primary and secondary introduction/spread across taxonomic groups and environments (Table
The three most frequently assigned CBD Pathway Classification framework subcategories associated with each broad taxonomic/environmental group for both introduction (primary pathway) and spread (secondary pathway). Rel – Release, Esc – Escape, Cont – Contaminant, Stow – Stowaway, Cor – Corridor, Un – Unaided (Hulme et al. 2008).
Taxonomic/ environmental group | Primary introduction | Secondary spread |
---|---|---|
Algae | Stow: Ship/boat hull fouling; Cont: Contaminant on animals (except parasites, species transported by host/vector); Stow: Ship/boat ballast water | Stow: Ship/boat hull fouling; Un: Natural; Stow: Angling/fishing equipment |
Microorganisms | Cont: Contaminant nursery material; Cont: Seed contaminant; Cont: Contaminant on plants (except parasites, species transported by host/vector) | Un: Natural; Cont: Contaminant nursery material; Cont: Transportation of habitat material (soil, vegetation,…) |
Marine and Freshwater invertebrates | Stow: Ship/boat ballast water; Stow: Ship/boat hull fouling; Cor: Interconnected waterways/basins/seas | Stow: Ship/boat ballast water; Stow: Ship/boat hull fouling; Contaminant on animals (except parasites, species transported by host/vector) Un: Natural |
Nematodes | Cont: Parasites on plants (including species transported by host and vector); Cont: Contaminant nursery material; Cont: Parasites on animals (including species transported by host and vector); Cont: Transportation of habitat material (soil, vegetation, …) | Cont: Parasites on animals (including species transported by host and vector); Cont: Transportation of habitat material (soil, vegetation, …); Cont: Contaminant nursery material |
Plants | Esc: Ornamental purpose other than horticulture; Cont: Seed contaminant; Esc: Horticulture | Cont: Seed contaminant; Stow: Machinery/equipment; Un: Natural |
Terrestrial invertebrates | Cont: Contaminant on plants (except parasites, species transported by host/vector); Cont: Food contaminant (including of live food); Cont: Contaminant nursery material | Cont: Contaminant on plants (except parasites, species transported by host/vector); Cont: Transportation of habitat material (soil, vegetation,…); Cont: Contaminant nursery material |
Vertebrates | Rel: Other intentional release; Rel: Fishery in the wild (including game fishing); Rel: Hunting | Un: Natural; Cor: Interconnected waterways/basins/seas |
The confidence levels of pathway assignments varied amongst the taxonomic groups. Pathways assigned to fungi and pathogens had the highest percentage of low confidence amongst groups, whereas vertebrates, plants and parasites were typically assigned with intermediate or high confidence (Fig.
Our study highlights that the importance of different pathways differs amongst taxonomic/environmental groups and for both primary introductions and secondary spread in Europe. However, it is apparent that some of the CBD Pathway Classification framework subcategories were not used at all or were relevant for only a few species (see Table
The ease of assigning pathway information using the CBD Pathway Classification framework depends on the availability of information. For many species, there was limited evidence available and many records were based on grey literature sources and consequently were assigned low confidence. This is highlighted also by
We are aware that the pre-selection of the species in this study may introduce biases. The dataset described in this study has a limited coverage of some large taxonomic groups (e.g. only about 400 species of plants were included from the 6600 species within the EASIN catalogue). Nevertheless, this pathway dataset covers about one third of the alien flora and fauna of Europe and so, we believe, the observed patterns of pathways have wide relevance. Furthermore, the analysis presented is limited by the fact that the pathways were not prioritised according to their relative importance, for example, in terms of rates of introduction or propagule number, because of lack of robust data. In addition, the importance of specific pathways can vary regionally and temporally (
The CBD Pathway Classification framework has value for underpinning prioritisation of pathways – to assist in development of policies and in their implementation, i.e. executing pathway management activities. It can be combined with assessments of impacts (
The terminology in the CBD Pathway Classification framework and in other broadly-used schemes is somewhat different. Although the CBD Pathway Classification framework provides a detailed level of pathway categories and subcategories, in a number of cases, the framework lacks a clear connection to trade and policy regulation terminology. Indeed, in other systems, a well-defined terminology for trade exists (e.g. International Plant Protection Convention/International Standards for Phytosanitary Measures, the EU Combined Nomenclature for custom and trade, https://comtrade.un.org). In addition, there is a plethora of possible combinations of pathways and vectors, some of which have been described in literature with specific terms (e.g. acclimatisation societies and gardens;
We argue that some of the CBD Pathway Classification framework subcategories or, rather, their descriptions, are not sufficiently distinct so their delimitation and interpretation, in some cases, overlap (see also
Some pathways are relatively specific (“Biological control”, “People and their luggage/equipment – in particular tourism”), while others are broader and less specific. Examples are the CBD pathway subcategories like “Seed contaminant”, “Contaminant on animals (except parasites and species transported by host/vector)” or “Timber trade”. These groups include a variety of different sources and vectors that can be controlled at borders and regulated. Specifically, the pathway “Contaminant on animals” is based on a number of activities, mainly related to the breeding of animals and trade with products derived from them. This subcategory applies, for example, to seeds/propagules on the fur or in the digestive tract of live animals, as well as to animal products (or by-products) – for example, on the skin and in the wool. It also includes, for example, transport in bedding. The pathway “Timber trade” includes logs, sawn timber and processed wood products (e.g. furniture) or sawdust and firewood. Similarly, the pathway “Seed contaminant” would be better split into at least two pathways as the risk of introduction differs greatly between contaminants of seeds for planting, compared with contaminants of seed that will be processed for food production (see our comment above and definition of “Food contaminant (including of live food) ” or as animal feed.
We are not recommending an increase of the hierarchical levels of the CBD Pathway Classification framework, but to adjust the width of the subcategories and their direct link to vectors and possible legislation management. In many cases there is a residual subcategory “other” (e.g. “Other intentional release”, “Other escape from confinement”), so that one possible approach would be to specify and split this residual subcategory, limiting the number of unclassified pathways. Adopting a nested structure in the pathway descriptions would need to be reflected in the database structures and most of the data would be available at a less detailed scale.
Furthermore, we found that it is difficult to separate the pathways for “Horticulture” and “Ornamental purposes other than horticulture”. The distinction is based on the risk or event of escape from a private garden compared to an escape from horticultural (commercial, industrial) facilities. Indeed, although the risk is vastly different, based on information available, there is often the possibility to use only a single pathway, that corresponds to Escape from culture/captivity: gardening. In the guidance document (
There was also some confusion in the use of the high level categories Stowaway and Contaminant. This appeared to be remedied following detailed consideration of the definitions within the Guidelines. On the one hand, experts agreed that, 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. The uncertainty arises where an alien species is typically associated with a substrate, but is able to survive away from it. These two subcategories are distinguished by the nature of the contaminated substratum; 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.
Parasitic alien species, whether in or on plants or animals, were mostly easy to categorise. The categories of pathways related to parasites, however, appear to be less useful in terms of managing the IAS, without the information on pathways applying to the host species (see, for instance, Navajas et al. 2012).
In aquatic environments, plastics or other human-made floating materials can travel considerable distances on ocean currents and are capable of transporting and spreading reproductively viable biota (see review in
Bilge waters are another issue for the aquatic environment and identified as an important vector. The metabarcoding analysis of 23 bilge samples collected from yachts and motorboats operating commercially and recreationally in two boating hubs in New Zealand’s South Island, led to the identification of five alien species, including the polychaete, Boccardia proboscidea (
The release of by-catch fish in commercial fishing can be a relevant pathway of secondary spread. This will depend on fishing and discard practices, with the highest risk from bottom trawlers. Survival rates of discarded fish (e.g. Plotosus lineatus in the Mediterranean Sea) are unknown, but can be high for some species. Such secondary spread was classified by
Assessments of presence and impact of IAS is always affected by the uncertainty in available data (
The biogeographic status of many species remains uncertain. These species are flagged as ‘cryptogenic’ when there is medium uncertainty about their origin, that is, whether they are native or alien or ‘data deficient’ when there is high uncertainty on their biogeographic status (
One of the greatest challenges experienced by the project team in assigning pathways based on the CBD Pathway Classification framework was ensuring the accurate classification of intentional releases from pathways classified only amongst those listed as “Escape from confinement”. A notable example is the “Pet/aquarium/terrarium species (including live food for such species)”. Indeed, this subcategory has been systematically used also to cover species which were introduced in a country intentionally for such purpose, but that either escaped in the environment accidentally or were released intentionally (for example, in the case of animals abandoned). Similarly, this may be the case also with other subcategories, such as “Live food/bait”, “Horticulture”, “Ornamental purpose other than horticulture” etc. (for example, in the case of live baits or cut plants dumped in the environment).
As stated in the guidelines on the CBD Classification Pathway framework (
A pathway framework needs to be based on sound science while flexibly accommodating the dynamic nature of biological invasions to satisfy policy and practitioner needs underpinning research and management of IAS. It is important that the compilation of information, such as pathways of introduction for alien species, follows global standards (see, as example, the Darwin Core Initiative;
It is essential that the experts, who assign pathways, openly share information and provide updates to the CBD Pathway Classification framework guidance to reduce ambiguity. To date, the broad hierarchical CBD Pathway Classification framework provides a tool which can be applied in diverse contexts, enabling rapid analysis of changing patterns and trends in biological invasions to be communicated rapidly and transparently, so that periodical updates will increase its value and effectiveness over time. However, it is essential that modifications are agreed collaboratively and communicated to everyone using the framework to reduce subsequent inconsistencies in use. We describe potential discrepancies and potential solutions to provide an updated CBD Pathway Classification framework (Table
Summary of some issues (including illustrative examples) and recommendations for changes to the CBD Pathway Classification framework or accompanying guidance document.
Topic | Issues | Example | Recommendation |
---|---|---|---|
Modification of subcategories | Pathway subcategory too broad and thus ambiguous | Seed contaminant | Divide into two subcategories: 1. contaminants of seeds for planting, 2. contaminants of seed that will be processed for food production or as animal feed |
Overlap amongst pathway subcategories | Agriculture, Horticulture, Ornamental purpose other than horticulture (horticulture is an industry process compared to ornamental purposes) | Ensure clear definitions, consistent with standard use in other sectors. Classify pathways to horticulture as a branch of agriculture separated clearly from ornamental use. | |
Revision of descriptions | Short pathway names attributed within the framework are unclear or ambiguous | Contamination on plants | Contamination on plants that are not part of the nursery trade |
Allow revisions based on new and emerging pathways | Vector does not correspond to the pathway category | Intentional release in the wild of aquarium kept species is different from unintentional Escape from Confinement. | Assign to the “Release” – Other intentional release or add a new vector category “Release”-aquarium/terrarium-zoo species |
Biological invasions are dynamic processes and there is a need to update the classification accordingly including emerging pathways | Floating marine litter | Assign floating marine litter to the pathway “Transport – stowaway” | |
Bilge waters as a secondary means of transport | Assign to the pathway “Transport – stowaway” other means of transport | ||
The release of by-catch fish in commercial fishing | Assign to “Transport-stowaway” Angling/fishing equipment” category. |
The authors gratefully acknowledge funding from European Commission funded study (ENV.B.2/SER/2015/0037rl) and the COST Action CA17122. JP and IP were partly supported by the Czech Ministry of Environment, project no. 20-10349J (Czech Science Foundation) and long-term research development project RVO 67985939 (Czech Academy of Sciences). HER and SR were partly supported by the Natural Environment Research Council award number NE/R016429/1 as part of the UK-SCAPE programme delivering National Capability. WR was partly supported by the project “Capacity building Neobiota” (Federal Ministry for Sustainability and Tourism) and MV by the Belmont Forum and BiodivERsA joint call for research proposals, under the BiodivScen ERA-Net COFUND programme funded by the Spanish Ministry of Science and Innovation (PCI2018-092939, MCIU/AEI/FEDER, UE). We are grateful for the many helpful comments received from Siobhan Edney, Wojciech Solarz, Quentin Groom and Tammy B. Robinson in revising this manuscript. The topic of the paper was discussed at a workshop on ‘Frameworks used in Invasion Science’ hosted by the DSI-NRF Centre of Excellence for Invasion Biology in Stellenbosch, South Africa, 11–13 November 2019, that was supported by the National Research Foundation of South Africa and Stellenbosch University.