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Ireland, being an island situated on Europe’s western seaboard, has a fewer number of native species than mainland European Union Member States (MS). Increased numbers of vectors and pathways have reduced the island’s biotic isolation, increasing the risk of new introductions and their associated impacts on native biodiversity. It is likely that these risks are greater here than they are in continental MSs, where the native biodiversity is richer. A horizon scanning approach was used to identify the most likely invasive alien species (IAS) (with the potential to impact biodiversity) to arrive on the island of Ireland within the next ten years. To achieve this, we used a consensus-based approach, whereby expert opinion and discussion groups were utilised to establish and rank a list of 40 species of the most likely terrestrial, freshwater and marine IAS to arrive on the island of Ireland within the decade 2017–2027. The list of 40 included 18 freshwater, 15 terrestrial and seven marine IAS. Crustacean species (freshwater and marine) were taxonomically dominant (11 out of 40); this reflects their multiple pathways of introduction, their ability to act as ecosystem engineers and their resulting high impacts on biodiversity. Freshwater species dominated the top ten IAS (seven species out of ten), with the signal crayfish (Pacifastacus leniusculus) highlighted as the most likely species to arrive and establish in freshwaters, while roe deer (Capreolus capreolus) (second) and the warm-water barnacle (Hesperibalanus fallax) (fifth), were the most likely terrestrial and marine invaders. This evidence-based list provides important information to the relevant statutory agencies in both the Republic of Ireland and Northern Ireland to prioritise the prevention of the most likely invaders and aid in compliance with legislation, in particular the EU Regulation on Invasive Alien Species (EU 1143/2014). Targeted biosecurity in both jurisdictions is urgently required in order to manage the pathways and vectors of arrival, and is vital to maintaining native biodiversity on the island of Ireland.
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Management of Biological Invasions (2020) Volume 11, Issue 2: 155–177
Lucy et al. (2020), Management of Biological Invasions 11(2): 155–177, 155
Research Article
Horizon scan of invasive alien species for the island of Ireland
Frances E. Lucy1,*, Eithne Davis1,*, Roy Anderson2, Olaf Booy3, Ken Bradley4, J. Robert Britton5, Colin Byrne6, Joseph M.
Caffrey7, Neil E. Coughlan8, Kate Crane8, Ross N. Cuthbert8, Jaimie T.A. Dick8, James W.E. Dickey8, Jeffrey Fisher9, Cathal
Gallagher10, Simon Harrison11, Matthew Jebb12, Mark Johnson13, Colin Lawton13, Dave Lyons14, Tim Mackie4, Christine Maggs5,
Ferdia Marnell14, Tom McLoughlin15, Dan Minchin16, Oonagh Monaghan15, Ian Montgomery8, Niall Moore3, Liam Morrison13,
Rose Muir4, Brian Nelson14, Art Niven17, Colette O’Flynn18, Bruce Osborne19, Ruth M. O’Riordan11, Neil Reid8, Helen Roy20,
Rory Sheehan1, Dorothy Stewart15, Monica Sullivan21, Paula Tierney22, Paula Treacy23, Elena Tricarico24 and Wayne Trodd15
1Centre for Environmental Research, Innovation and Sustainability, Dept. of Environmental Science, Institute of Technology, Ash Lane, Sligo, Ireland,
2Royal Entomological Society, Belfast, Northern Ireland, 3GB Non-native Species Secretariat, Sand Hutton, York, UK, 4Department of Agriculture,
Environment and Rural Affairs, Dundonald House, Upper Newtownards Road, Ballymiscaw, Belfast, Northern Ireland, 5University of Bournemouth,
Poole UK, 6Dept of Housing, Planning and Local Govt., Custom House, Dublin, Ireland, 7INVAS Biosecurity Ltd., 82 Lakelands Close, Stillorgan, Co
Dublin, Ireland, 8Institute for Global Food Security, School of Biological Sciences, Queen’s University Belfast, 19 Chlorine Gardens, Belfast, BT9 5DL,
Northern Ireland, UK, 9Marine Institute, Rinville, Oranmore, Co. Galway, Ireland, 10Inland Fisheries, 3044 Lake Drive, Citywest Business Campus,
Dublin 24, Ireland, 11School of Biological, Earth and Environmental Sciences and the Environmental Research Institute, University College, Cork, Cork
City, Ireland, 12Office of Public Works, National Botanic Gardens, Glasnevin, Dublin, Ireland, 13National University of Ireland, Galway, Ireland,
14National Parks and Wildlife Service, 90 North King Street, Dublin, Ireland, 15Environmental Protection Agency, Clondalkin, Dublin, Ireland, 16Marine
Organisms Investigation, Killaloe, Co. Clare, Ireland, 17Loughs Agency, 22 Victoria Road, Londonderry, Northern Ireland, 18National Biodiversity Data
Centre (Ireland), WIT West Campus, Carriganore, Waterford, Ireland, 19UCD school of Biology and Environmental Science and UCD Earth Institute,
University College Dublin, Belfield, Dublin 4, Ireland, 20UK Centre for Ecology and Hydrology, Maclean Building, Crowmarsh Gifford, Wallingford, Oxon,
UK, 21Jennings O’Donovan and Partners Limited, Finisklin Business Park , Sligo, Ireland, 22Department of Botany, School of Natural Sciences, Trinity
College Dublin, Dublin 2, Ireland, 23Waterways Ireland, 2 Sligo Road, Enniskillen, Co Fermanagh, Northern Ireland, 24University of Florence, Via
Madonna del Piano 6, 50019 Sesto Fiorentino, Florence, Italy
Author e-mails: (FEL), (ED), (DM), (OM), (IM), (NM), (LM), (RM), (BN), (AN), (COF), (BO), (RO), (PTi), (NR), (HER), (RS), (DS), (MS), (PTr), (ET), (WT)
*Сorresponding joint first authors
Ireland, being an island situated on Europe’s western seaboard, has a fewer number of native
species than mainland European Union Member States (MS). Increased numbers of vectors and
pathways have reduced the island’s biotic isolation, increasing the risk of new introductions
and their associated impacts on native biodiversity. It is likely that these risks are greater
here than they are in continental MSs, where the native biodiversity is richer. A horizon
scanning approach was used to identify the most likely invasive alien species (IAS) (with the
potential to impact biodiversity) to arrive on the island of Ireland within the next ten years.
To achieve this, we used a consensus-based approach, whereby expert opinion and discussion
groups were utilised to establish and rank a list of 40 species of the most likely terrestrial,
freshwater and marine IAS to arrive on the island of Ireland within the decade 2017–2027.
The list of 40 included 18 freshwater, 15 terrestrial and seven marine IAS. Crustacean
species (freshwater and marine) were taxonomically dominant (11 out of 40); this reflects
their multiple pathways of introduction, their ability to act as ecosystem engineers and their
resulting high impacts on biodiversity. Freshwater species dominated the top ten IAS (seven
species out of ten), with the signal crayfish (Pacifastacus leniusculus) highlighted as the most
likely species to arrive and establish in freshwaters, while roe deer (Capreolus capreolus)
(second) and the warm-water barnacle (Hesperibalanus fallax) (fifth), were the most likely
terrestrial and marine invaders. This evidence-based list provides important information to
the relevant statutory agencies in both the Republic of Ireland and Northern Ireland to
prioritise the prevention of the most likely invaders and aid in compliance with legislation, in
particular the EU Regulation on Invasive Alien Species (EU 1143/2014). Targeted biosecurity
in both jurisdictions is urgently required in order to manage the pathways and vectors of
arrival, and is vital to maintaining native biodiversity on the island of Ireland.
Key words: signal crayfish, freshwater, marine, terrestrial, biosecurity, biodiversity,
Citation: Lucy FE, Davis E, Anderson R,
Booy O, Bradley K, Britton JR, Byrne C,
Caffrey JM, Coughlan NE, Crane K,
Cuthbert RN, Dick JTA, Dickey JWE,
Fisher J, Gallagher C, Harrison S, Jebb M,
Johnson M, Lawton C, Lyons D, Mackie
T, Maggs C, Marnell F, McLoughlin T,
Minchin D, Monaghan O, Montgomery I,
Moore N, Morrison L, Muir R, Nelson B,
iven A, O’Flynn C, Osborne B,
O’Riordan RM, Reid N, Roy H, Sheehan
R, Stewart D, Sullivan M, Tierney P,
Treacy P, Tricarico E, Trodd W (2020)
Horizon scan of invasive alien species for
the island of Ireland. Management of
iological Invasions 11(2): 155–177,
Received: 3 October 2019
Accepted: 9 April 2020
Published: 27 April 2020
Handling editor: Vadim E. Panov
Copyright: © Lucy et al.
This is an open access article distributed under t erms
of the Creative Commons Attribution License
(Attribution 4.0 International - CC BY 4.0).
Horizon scan of invasive alien species for the island of Ireland
Lucy et al. (2020), Management of Biological Invasions 11(2): 155–177, 156
Invasive alien species (IAS) are widely recognised as one of the greatest
threats to biodiversity, particularly through their interactions with other
drivers of change (Millenium Ecosystem Assessment 2005; Vilá et al. 2011;
Blackburn et al. 2015; Dick et al. 2017; IPBES 2019). Predicting the arrival,
establishment, spread and impact of IAS to any region is a challenging task;
nevertheless, establishing a list of likely candidate species is a vitally
important first step in complying with legislation (EU 2014) and mitigating
the environmental and economic impacts associated with an established
IAS. This information can then be promptly used to direct policy and
target resources, on a national or cross-jurisdictional level, towards
prevention, early detection and rapid response for the most impactful IAS.
Ireland, being an island, has fewer native species than mainland Europe,
and therefore the potential impacts of damage to biodiversity by IAS are
greater than in mainland Europe (Simberloff 1995; Stokes et al. 2006a;
Cabot 2009). A workshop entitled, “Identification of emerging Invasive
Alien Species with the potential to threaten biodiversity in Ireland” was
held in April 2017 at the Institute of Technology, Sligo, Ireland. The
workshop applied a horizon scan process to forecast IAS arrival,
establishment and impact for the island of Ireland (both jurisdictions) and
was attended by experts from the Republic of Ireland, Northern Ireland,
and Great Britain. These experts were selected from a range of disciplines
(scientific researchers, practitioners and responsible authorities) in order
to provide a balance of expertise throughout terrestrial, freshwater and
marine taxa.
Horizon scanning is the systematic process of conducting a contextualised
search for potential threats and opportunities that need identification, to
inform future decision-making and policy development (Sutherland et al.
2011; Peyton et al. 2019; Roy et al. 2014, 2019; Vilá et al. 2009). This is an
essential tool for anticipating which IAS are most likely to arrive and which
will cause the greatest impacts, such that preventative action can be taken.
Accordingly, horizon scanning is recognised as an essential component in
IAS management (Roy et al. 2015, 2019) and has been specifically used in
several IAS exercises, such as: 1) identifying emerging IAS with the potential
to threaten biodiversity in Great Britain (Roy et al. 2014); 2) prioritising
prevention efforts for the introduction of IAS in the EU (Roy et al. 2015,
2019); and 3) identifying the top twenty key issues relating to IAS in
Europe (Caffrey et al. 2014). In these studies and others (Parrott et al. 2009;
Gallardo and Aldridge 2013), horizon scanning was utilised as an effective
screening tool to identify potential IAS invasions and associated impacts,
and also to inform efficient and effective management techniques.
The systematic approach for IAS identification differentiates horizon
scanning from other, less robust, processes such as stand-alone literature
searches and trend analysis (Sutherland and Woodroof 2009). Relevant
Horizon scan of invasive alien species for the island of Ireland
Lucy et al. (2020), Management of Biological Invasions 11(2): 155–177, 157
evidence is obtained through literature, databases and expert knowledge. A
horizon scanning exercise consists of several distinct phases and when
effectively undertaken, provides decision-makers with information on
which to base cogent but flexible strategies and plans for future
environmental management (Sutherland and Woodroof 2009). Horizon
scanning provides opportunities for conservation biology to be a proactive
rather than a reactive science (Sutherland et al. 2018) where it can be used
in a consensual process to prioritise prevention efforts for introduction of
IAS (Roy et al. 2015, 2019) and to help inform rapid response measures to
those IAS recently introduced (Caffrey et al. 2014).
The main aim of this work was to produce a list of the top 10 IAS in
order of priority with a further continued ranking of the next 30 species most
likely to arrive, establish and cause impacts to biodiversity in terrestrial,
freshwater and marine biomes on the island of Ireland within the decade
2017–2027. A workshop was organised to generate this list, which can
inform the statutory agencies and other concerned stakeholders in both
jurisdictions in the need to prioritise the prevention, surveillance and rapid
response for the most likely invaders. Pathways of introduction were also
addressed to determine the most likely routes of introduction for these
species to inform on biosecurity strategies for the management of these
pathways. This exercise focussed on the pathways of introduction specific
to Ireland, and serves to enhance the pathway analysis as carried out by MSs.
Materials and methods
For this horizon scan of IAS, we used an adapted version of the consensus
method used by Roy et al. (2014) as outlined here. The main deviation
from the Roy et al. methodology was in reducing the number of expert
groups to three habitats, and focussing on pathways appropriate to the
island of Ireland. The process involved two distinct phases.
1. Preliminary consultation between groups of experts in Freshwater,
Terrestrial, and Marine species.
2. Consensus building among and between expert groups to provide a
ranked list of species mostly likely to invade the island of Ireland,
based on the probability of the arrival, establishment and impact of
individual species.
Preliminary Consultation
Twenty-three experts in the marine, freshwater and terrestrial ecology were
selected to complete the preliminary consultation phase of the study. This
took place five months in advance of the workshop, and involved ecologists
from both the Republic of Ireland and Northern Ireland. These were
assigned to groups comprised of between 7–8 experts that included a group
Horizon scan of invasive alien species for the island of Ireland
Lucy et al. (2020), Management of Biological Invasions 11(2): 155–177, 158
leader, co-leader/rapporteur and the core group. Experts were assigned to
groups according to their complimentary expertise across taxa, with the
intention of ensuring the best possible balance of expertise within each
biome group, and within the workshop as a whole. When participants had
confirmed their availability, they were provided with baseline information
regarding the workshop and detailed information followed in March 2017.
Each expert received a group-relevant list of IAS (via email), selected
from six relevant sources: (1) the species identified previously as High Risk
in the GB horizon scanning for IAS (Roy et al. 2014), (2) the previous
Invasive Species Ireland horizon scan (O’Flynn et al. 2014), (3) a marine list
(Minchin 2014), (4) Non-native species APplication based Risk Analysis
for Ireland (NAPRA 2014) major risk species, and (5) species not currently
established in Ireland pursuant with the 37 species named in the EU Invasive
Alien Species Regulation 1143/2014 and the EU Implementing Regulation
(EU) 2016/1141 of 13 July 2016 adopting a list of IAS of Union concern.
Experts were invited to use these or alternative sources to suggest other
IAS that may be likely to arrive, establish, spread and impact on native
biodiversity within the next decade, together with supporting evidence
(generally peer-reviewed publications but also grey literature, where the
former was lacking). Experts were provided with relevant reference sources
(MSFD 2012; Kelly et al. 2013a; Roy et al. 2014, 2015) and databases (e.g.
DAISIE, NOBANIS, EASIN, GISID, CABI, EPPO), but were also asked to
review and, if necessary, supplement these using other literature sources
and their own and others’ expert opinion. Suggested additional species
proposed by individual experts were circulated to the expert group as a
whole in advance of the workshop by the group leader, along with details
of supporting literature. These additional species were brought forward for
discussion in detail within the group. The total number of IAS that were
assessed during this study was 348, with 80 marine, 87 freshwater and 181
terrestrial species (Figure 1).
Each expert group was provided with a spreadsheet template to ensure
consistency in the collated information. Table columns had the following
headings: species, taxonomic group, functional group, native range, likely
pathway of arrival, and uncertainty (see below).
Guidance notes were provided. Functional groups were classified as
primary producer, herbivore, omnivore, predator and parasite. Pathways
of arrival were defined following IUCN classification (UNEP/CBD/
SBSTTA/18/9/Add.1). Management of species or pathways was not to be
considered. The likelihood of arrival, likelihood of establishment/spread
and likelihood of impact on biodiversity was scored from 1 (very unlikely)
to 5 (very likely). Impact on biodiversity was assessed by considering the
following parameters, adapted from Branquart (2007) as used by Roy et al.
Horizon scan of invasive alien species for the island of Ireland
Lucy et al. (2020), Management of Biological Invasions 11(2): 155–177, 159
Figure 1. Consideration and consensus process for horizon scanning of IAS in Ireland.
1. Dispersal potential
2. Colonization of high conservation value habitats
3. Adverse impacts on native species:
a) Predation/herbivory
b) Competition
c) Transmission of pathogens and parasites to native species
d) Genetic effects
4. Alteration of ecosystem functions:
a) Modification to nutrient cycling
b) Physical modifications to the habitat
c) Modifications of natural successions
d) Disruption of food webs
An overall score for each species was determined as the product of the
scores for likelihood of arrival (A), establishment (B) and impact (C)
(maximum score = 125). Uncertainty was defined as the level of uncertainty
on the overall assessment in terms of the quantum and quality of the
information available on the particular species and also in terms of the
overall uncertainty in the species’ assessment (Kelly et al. 2013b). This was
ranked as low, medium, high and very high, with the most certain invasions
Horizon scan of invasive alien species for the island of Ireland
Lucy et al. (2020), Management of Biological Invasions 11(2): 155–177, 160
as low and the most uncertain as very high. Uncertainty scores were taken
into account during the expert group discussions.
An agreed ranked list of IAS was produced by each group. This
preliminary consultation phase was conducted over a three week period.
The scores derived were only used to provide guidance for ranking the
species, enabling a starting point for consensus, from which experts, across
the three groups, could engage in debate, leading to modification of the
score in some cases. For transparency, we retained the original scores. Only
species considered as having a medium or high probability (scores of 3 or
above) in all categories (arrival, establishment and impact) were taken
forward to the next phase of the process, i.e. consensus-building across
expert groups.
Consensus-building across expert groups
Consensus-building across the three expert groups took place at a
workshop held at the Institute of Technology, Sligo on April 19th and 20th
2017. The workshop was held over two days, led by an independent chair
and two technical facilitators. Three representatives from relevant GB
statutory agencies and one Irish agency were invited to observe the process
and contribute to methodological discussion.
The first meeting involved the chairperson, technical facilitators and
group leaders to provide an overview of the IAS within their lists, with
particular emphasis on justification of scores. The aim of this exercise was
both to review the three lists and to ensure standardization of the approach
to scoring during the preliminary consultation. Discussions between group
leaders enabled the moderation of group scores, to create an aggregated,
ranked list of species for each of the three biome groups.
All expert group participants joined the workshop for a short plenary
session explaining the workshop process. The experts then immediately
joined their respective group leaders and groups to review and refine the
ranked list of IAS. Expert group participants were invited to make
challenges for or against species within the lists. The combined expert
opinion within groups was used to further refine the ranking. Throughout
the discussions, the group provided expert opinion to support the decision-
making process and the scores were used only as guidance for this process.
The discussions enabled participants to review available information and
consider uncertainty in preparation for the final session. The processes of
collaborative review and consensus-building were repeated until the entire
group had converged on a ranked list at the end of the afternoon. At the
end of Day 1 the group leaders and co-leaders met with the chairperson,
technical facilitators and observers to review the ranking among the groups.
On Day 2, all participants reconvened within their groups to review and
refine the compiled and ranked list of IAS which would be brought
forward to the concensus session. Ultimately, consensus was reached
Horizon scan of invasive alien species for the island of Ireland
Lucy et al. (2020), Management of Biological Invasions 11(2): 155–177, 161
within groups on the basis of expert opinion provided through open
discussion (a transparent process in which questions were openly asked
and defences were given or opinions were modified) and majority voting.
Discussions were most detailed for species ranked as high impact (with a
high degree of certainty) within the aggregated list. This filtering resulted
in 24 marine species, 55 freshwater species and 107 terrestrial species (total
number/species = 186) being brought forward for the final consensus
(Figure 1). The group sessions then concluded.
Day 2 continued with a final plenary synthesis session, involving all
experts working together to determine the top ranked species likely to
arrive, establish and impact on native biodiversity in the next ten years.
Species were primarily ranked within a Top Ten by total score. Species
ranked from 11–40 were also included as they were considered important
for horizon scan purposes. Ranking of impact scores was also considered in
the case of identical scores, with precedence given, in general, to those with
higher impact score. Once consensus was reached, the workshop ended.
The top forty IAS most likely to arrive, establish, spread and cause impacts
to biodiversity on the island of Ireland are shown in Table 1, with a
summary profile for each of the top ten species available in supplementary
material Appendix 1. Supplementary Tables S1–S3 include all of the species
that were considered in each of the freshwater, marine and terrestrial
sessions. Information is provided on taxonomic and functional feeding
groups, environment, native range, pathways of arrival and uncertainty for
each species.
Fourteen of the 40 IAS are predators, eleven are herbivores (including
three plant pests), six are omnivores, four are filter feeders, four are
primary producers and one is a parasite. All six of these functional feeding
groups are represented in the Top Ten species (Table 1).
The signal crayfish (Pacifastacus leniusculus Dana, 1852) was scored as
the most likely species to arrive, establish and create impacts on biodiversity
in Ireland (score = 125). Second was the Roe deer (Capreolus capreolus
Linnaeus, 1758). Killer shrimp (Dikerogammarus villosus Sowinsky, 1894),
salmon fluke (Gyrodactylis salaris Malmberg, 1957) and warm water
barnacle (Hesperibalanus fallax Broch, 1927) were ranked as species three
to five in the top ten list. These five species had the highest values for
biological impact (5), with associated scores of 4 to 5 for arrival and
establishment. The uncertainty scores for these species were also low for
the signal crayfish, roe deer, killer shrimp and salmon fluke, indicating a
high probability of invasion success for each of these species.
Freshwater species dominated the top ten species (seven of the top ten);
in addition to signal crayfish, killer shrimp and salmon fluke, the others
were floating pennywort (Hydrocotyle ranunculoides L.f. – ranked 6th), quagga
Horizon scan of invasive alien species for the island of Ireland
Lucy et al. (2020), Management of Biological Invasions 11(2): 155–177, 162
Table 1. Top 40 species emerging from horizon scan for Ireland. Species were scored according to their likelihood of arrival (A),
their likelihood of establishing in the wild (B), and their impact on biodiversity (C). They were then ranked according to the
product of those scores, taking uncertainty (UNCERT) into consideration. Prioritisation of species was based on the highest scoring
paired with the highest uncertainty. For full list of Pathway Codes, see Table 2.
Rank Species Common
Group Environment Native Range Pathway of
1 Pacifastacus
crayfish Crustacean Omnivore Freshwater North
5 5 5 125 Low
2 Capreolus
capreolus Roe deer Mammal Herbivore Terrestrial Europe,
Middle East M/R/HW 5 4 5 100 Low
3 Dikerogammarus
villosus Killer shrimp Crustacean Predator Freshwater Ponto-caspian V/TS/FE 5 4 5 100 Low
4 Gyrodactylus
salaris Salmon fluke Monogenean Parasite Freshwater Baltic Sea V/TS/FE 4 5 5 100 Low
5 Hesperibalanus
barnacle Crustacean Filter
feeder Marine
Atlantic coast
of tropical
V/TS/HF 5 5 4 100 Medium
6 Hydrocotyle
pennywort Plant Primary
producer Freshwater
North and
South America,
V/TS/S 5 5 4 100 High
mussel Mollusc Filter
feeder Freshwater Ponto Caspian V/TS/S 4 4 5 80 Low
8 Caulacanthus
weed Alga Primary
producer Marine Japan, NW
Pacific M/E/A 5 5 3 75 Low
9 Eriocheir
mitten crab Crustacean Predator Freshwater Eastern Asia V/TS/S 5 3 5 75 Low
10 Pseudorasbora
Stone moroko
Crustacean Predator Freshwater NW Pacific V/TS/FE 3 5 5 75 Medium
11 Ondatra
zibethicus Muskrat Mammal Herbivore Terrestrial North
America M/R/O 5 5 3 75 Medium
12 Psittacula
parakeet Bird Herbivore Terrestrial South Asia S/U/ND 5 4 3 60 Medium
13 Agrilus
Emerald ash
borer Insect Herbivore/
plant pest Terrestrial
E Asia,
E central
China, Japan,
M/E/H 4 3 4 48 High
14 Agrilus anxius Birch borer Insect Herbivore/
plant pest Terrestrial North
M/E/H 4 3 4 48 High
15 Ensis leei American
razor-clam Mollusc Filter
feeder Marine NW Atlantic V/TS/BW;
M/E/A 5 5 2 50 Medium
16 Dikerogammarus
shrimp Crustacean Predator Freshwater Ponto-caspian V/TS/FE 5 4 3 60 Medium
17 Orconectes
crayfish Crustacean Omnivore Freshwater Ponto-caspian M/E/PAS 4 3 5 60 Medium
18 Oncoryhnchus
Trout Fish Predator Freshwater North America M/R/FW;
M/E/A 5 3 4 60 Medium
19 Squalius
cephalus Chub Fish Predator Freshwater Europe M/R/FW 4 4 3 48 Low
primrose Plant Primary
producer Freshwater South
America V/TS/S 4 3 4 48 Low
21 Microtus
agrestis Field vole Mammal Herbivore Terrestrial Europe M/TC/HM 4 4 3 48 Medium
22 Cochlicella
barbara Pointed snail Mollusc Herbivore/
plant pest Terrestrial Europe 5 5 1 25 Medium
23 Procyon lotor Raccoon Mammal Omnivore Terrestrial
North and
M/E/BG 4 3 4 48 Medium
24 Tamias sibiricus Siberian
chipmunk Mammal Herbivore Terrestrial
Northern Asia
to Japan)
M/E/PAS 5 3 3 45 Medium
25 Hemigrapsus
shore crab Crustacean Predator Marine Asia (Pacific) V/TS/HF 4 4 3 48 Medium
26 Thymallus
thymallus Grayling Fish Predator Freshwater Europe M/R/FW 2 5 4 40 Medium
27 Barbus barbus Barbel Fish Predator Freshwater Europe M/R/FW 4 4 3 48 Medium
28 Sander
Pikeperch Fish Predator Freshwater Europe M/R/FW 4 3 4 48 Medium
29 Orconectes
virilis Virile crayfish Crustacean Omnivore Freshwater North America M/E/PAS 4 3 4 48 Medium
30 Obama nungara Flatworm Trematode Predator Terrestrial South America M/TC/HM 5 3 3 45 High
31 Myriophyllum
water-milfoil Plant Primary
producer Terrestrial North America M/E/O 3 4 4 48 High
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Lucy et al. (2020), Management of Biological Invasions 11(2): 155–177, 163
Table 1. (continued) . Top 40 species emerging from horizon scan for Ireland.
Rank Species Common
Group Environment Native Range Pathway of
32 Hylastes ater Black pine
bark beetle Insect Herbivore/
plant pest Terrestrial Europe, Asia –
China, Korea M/TC/P 4 4 3 48 High
33 Salvelinus
Brook trout;
Brook charr;
Sea trout
Fish Predator Freshwater North America M/R/FW;
M/E/A 3 4 4 48 High
34 Astacus astacus
Noble Crayfish;
Crustacean Omnivore Freshwater Europe M/E/PAS 4 3 4 48 High
35 Celtodoryx
ciocalyptoides sponge Sponge Filter
feeder Marine NW Pacific M/E/A 4 4 3 48 Very High
36 Hemigrapsus
Asian shore
crab Crustacean Omnivore Marine Asia (Pacific) V/TS/BW;
M/E/A 4 4 3 48 May be
here already
37 Myiopsitta
Monk parakeet;
Bird Herbivore Terrestrial South
America M/E/PAS 4 4 2 32 Low
38 Orconectes
rusticus Rusty crayfish Crustacean Predator Freshwater
North America
(Ohio river
M/E/PAS 3 2 5 30 Low
39 Microtus arvalis Orkney vole Mammal Herbivore Terrestrial Orkney Islands,
Scotland M/TC/HM 3 4 3 36 Medium
40 Threskiornis
Sacred Ibis;
Sacred Ibis
Bird Predator Terrestrial Sub-Saharan
Africa S/U/ND 4 3 3 36 Medium
Figure 2. Freshwater species made up the greatest proportion of the horizon scan list for
Ireland, followed by terrestrial species. Marine species made up the smallest group on the list.
mussel (Dreissena rostriformis bugensis Andrusov, 1897 – ranked 7th),
chinese mitten crab (Eriocheir sinensis H. Milne-Edwards, 1853 – ranked 9th)
and topmouth gudgeon (Pseudorasbora parva Bleeker, 1859 – ranked 10th).
The marine pom-pom weed (Caulacanthus okamurae Yamada, 1933) was
ranked at number 8.
The final list of top 40 species which will be a valuable resource for
decision-making around IAS in Ireland includes eighteen freshwater, seven
marine and fifteen terrestrial IAS (Table 1, Figure 2). Eleven of the forty
Terrestrial‐ 15
Freshwater‐ 18
Marine‐ 7
Terrestrial Freshwater Marine
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Lucy et al. (2020), Management of Biological Invasions 11(2): 155–177, 164
Table 2. IUCN Pathway codes.
Category Subcategory Code
Movement of
Release in nature
Biological control M/R/B
Erosion control/dune stabilisation (windbreaks, hedges…) M/R/EC
Fishery in the wild M/R/FW
Hunting in the wild M/R/HW
Landscape/flora/fauna "improvement in the wild M/R/L
Introduction for conservation purposes or wildlife management M/R/C
Release in nature for use (other than above, e.g. fur, transport, medical use) M/R/U
Other intentional release M/R/O
Agriculture M/E/AG
Aquaculture/mariculture M/E/A
Botanical garden/zoo/aquaria M/E/BG
Farmed animals M/E/FA
Forestry M/E/F
Fur farms M/E/FF
Horticulture M/E/H
Ornamental purpose M/E/O
Pet/aquarium species M/E/PAS
Research (in facilities) M/E/R
Live food and live baits M/E/FB
Other escape from confinement M/E/O
Transport - Contaminant
Contaminant nursery material M/TC/NM
Contaminated bait M/TC/B
Food contaminant M/TC/F
Contaminant on animals M/TC/A
Contaminant on plants M/TC/P
Parasites on animals M/TC/PA
Parasites on plants M/TC/PP
Seed contaminant M/TC/S
Timber trade M/TC/TT
Transportation of habitat material M/TC/HM
Subclass Undefined M/TC/U
Vector Transport - stowaway
Container/bulk V/TS/CB
Hitchhikers in or on plane V/TS/P
Hitchhikers on ship/boat V/TS/S
Machinery/equipment V/TS/M
People and their luggage/equipment V/TS/L
Ship/boat ballast water V/TS/BW
Ship/boat hull fouling V/TS/HF
Vehicles V/TS/V
Other means of transport V/TS/T
Angling/fishing aquaculture equipment V/TS/FE
Organic packing material V/TS/PM
Subclass Undefined V/TS/U
Interconnected waterways/basins/seas S/C/WS
Tunnels and land bridges S/C/TB
Subclass Undefined S/C/U
Unaided Natural dispersal across borders S/U/ND
Unknown Unknown S/U/U
species are crustaceans, with two freshwater amphipods (killer shrimp
(Dikerogammarus villosus) and demon shrimp (Dikerogammarus
haemobaphes)), seven decapods (including five freshwater crayfish, two
marine crabs and one freshwater crab) and the warm-water barnacle.
Freshwater fishes and terrestrial mammals are the next most common
groups with seven and six species, respectively, listed in the Top 40. In terms
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Lucy et al. (2020), Management of Biological Invasions 11(2): 155–177, 165
Figure 3. Pathway categories of introduction for freshwater, marine and terrestrial species.
of taxonomy, the remaining 16 species include: three birds, three
freshwater plants, three molluscs (one from each of the three biomes),
three insects (all terrestrial beetles), two trematode parasites (freshwater
and terrestrial), one marine alga and one marine sponge.
The native range of the IAS in the list is trans-global (Table 1). Most of
the freshwater fishes are European species, the quagga mussel, killer and
demon shrimp (Dikerogammarus haemobaphes (Eichwald, 1841)) are
Ponto-Caspian in origin. Some of the species that are native in Africa, the
Americas and Asia are already present in Europe (e.g. ring-necked parakeet
(Psittacula krameri (Scopoli, 1769)), rainbow trout (Oncorhynchus mykiss
(Walbaum, 1792)), and floating pennywort (Hydrocotyle ranunculoides L.f.)).
Pathways of arrival for the Top 40 species are indicated in Figure 3.
Escape (all three environments), transport stowaway (freshwater and
marine) and transport contaminant (terrestrial) are the main pathways
identified. Release into nature was an important component for both
freshwater and terrestrial species. Unaided natural dispersal across borders
was also identified for two of the bird species.
Freshwater Marine Terrestrial
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The list of the Top 40 IAS that are most likely to arrive on the island of
Ireland provides an essential resource for targeted invasive species
management in both the Republic of Ireland and Northern Ireland. The
consensus-building approach used for the Great Britain IAS horizon scan
(Roy et al. 2014) was used here to combine the individual and team
knowledge of experts across freshwater, marine and terrestrial biomes.
The IAS in the top 40 include representatives from a range of functional
groups across freshwater, terrestrial and marine environments and with
native distributions over a range of global regions. The origin of spread to
Ireland for these “door-knockers” (NOBANIS 2015) may not be within
native ranges, as transport and trade routes with Great Britain and continental
Europe can provide opportunities for introductions of IAS already
established there. For example, there is a rapid increase in the rate of new
arrivals into Europe from temperate Asia (Roy et al. 2012) and at least 35
Ponto-Caspian species have arrived into Western Europe over the past
three decades due to the interconnectivity of European waterways (Bij de
Vaate et al. 2002). This Irish horizon scan ranks North American signal
crayfish (Pacifastacus leniusculus) as the number one species most likely to
invade Ireland and cause the greatest impact. This particular species is the
most widespread alien crayfish in Europe (29 invaded territories as defined
by Kouba et al. 2014, GB included), introduced for stocking and aquaculture
purposes (Kouba et al. 2014). It is omnivorous, highly prolific (up to 400
eggs per female, mature at age 2–3), can live to 20 years. and is adaptable to
a wide range of environments. Pacifastacus leniusculus is a carrier of the
crayfish plague (Aphanomyces astaci – strains B and C) (OIE 2019), which
is lethal for the Irish population of Austropotamobius pallipes (white clawed
crayfish), having a 100% mortality rate. Its feeding habits, burrowing
activity, reproductive rate and aggressiveness has a highly destructive effect
on invaded ecosystems, allowing it to outcompete native crayfish, reducing
local biodiversity and stability of river banks (Mazza et al. 2018; Veselý et
al. 2015). Pacifastacus leniusculus is included in the List of Species of Union
Concern which is annexed to the EU Regulation on IAS 1143/2014. Its
management is challenging, requiring an integrated approach (Stebbing et
al. 2014). Prevention of its introduction is recommended as by far the most
practical approach.
The top species in the horizon scan were selected on the basis of
probability of arrival, establishnment and biological impacts, giving us
some insight into the dispersal of those high-scoring species between the
freshwater, terrestrial and marine environments. Freshwater IAS are
known as high impact invaders in many ecosystems in Europe and North
America (Tricarico et al. 2010; Strayer 2010; Ricciardi and MacIssac 2011;
Caffrey et al. 2011; O’Flynn et al. 2014; Lucy et al. 2013). This is reflected in
the results of this horizon scan where seven out of the top ten ranked
species are freshwater IAS.
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There are five crayfish species present in the Irish horizon scan list.
Crayfish are one of the most widely introduced freshwater taxa, usually
introduced intentionally for aquaculture or ornamental reasons. Given
their ability to adapt to a variety of conditions and to disperse over land,
they often negatively and seriously impact the invaded ecosystems,
(Thomas et al. 2019; Twardochleb et al. 2013).
Topmouth gudgeon (Pseudorasbora parva) is a small-bodied fish (< 10 cm)
of the Cyprinidae family, originating from East Asia (Gozlan et al. 2010). It
was introduced accidentally into Eastern Europe in the 1960s via the
aquaculture trade. Its further spread in Europe has resulted from natural
dispersal from aquaculture sites (Gozlan et al. 2010). Topmouth gudgeon
has a high phenotypic plasticity in the expression of their life history traits,
such as in their somatic growth rates and reproductive traits (e.g. fecundity,
length and age at maturity, which has greatly facilitated its capacity to
establish new populations and then colonise new waters (Britton and
Gozlan. 2013). Whilst there is some concern over its negative ecological
interactions with native fishes (Tran et al. 2015), the primary concern of its
invasion is its potential transmission of the novel (and lethal) pathogen rosette
agent (Sphaerothecum destruens) (Andreou et al. 2012; Sana et al. 2018).
Salmon fluke (Gyrodactylus salaris) is a small (< 1 mm) parasite that
infects the skin, gills and fins of salmon, trout and some other species of
freshwater fish (MI and IFI 2012). It causes gyrodactylosis, a serious
notifiable disease that represents one of the biggest threats to the salmon
population in Ireland. It is present in most countries of Europe and
Scandinavia, although is currently absent from both Ireland and Great
Britain. Based on experience in countries with Atlantic salmon populations
that have become infected, if G. salaris establishes itself in Ireland, it could
bring about a catastrophic collapse of the salmon stocks (Johnsen and
Jensen 1986). It has several possible pathways of introduction, the most
significant of which is the illegal importation of infected fish. Next in
importance is the introduction of the parasite on contaminated fishing
equipment. The parasite is very hardy and is capable of surviving for
several days in damp conditions on wet angling equipment (e.g. wet
landing nets, waders).
Killer shrimp (Dikerogammarus villosus), number three on the horizon
scan list, is present in Great Britain (MacNeil et al. 2010), listed officially as
“Occasional or few reports” (Dodd et al. 2014), but widely acknowledged as
being established in GB catchments. Native to the Black Sea and Caspian
Sea, it is a relatively recent invader in Europe, but has now been recorded
in all major rivers in mainland Europe (Devin and Beisel 2006) with the
primary vector of spread over long distances being ballast water and the
hulls of boats (MacNeil et al. 2010). The likelihood of introduction of this
species into Ireland has been assessed as “high” (risk of introduction = five),
with a low level of uncertainty. Dikerogammarus villosus is tolerant of a
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wide range of habitats, freshwater and brackish (Bruijs et al. 2001), both
lentic and lotic systems, and has a high reproductive rate (Pöckl 2007),
making it highly likely to establish successfully on introduction to Ireland.
Its impact on biodiversity is high, showing extremely aggressive behaviour
towards native invertebrate species and causing significant changes in
food-web dynamics (Dick and Platvoet 2000; Dick et al. 2002).
Chinese mitten crab (Eriocheir sinensis) is a large migrating crab with
dense mats of hair (mittens) on its white-tipped claws. It is native to
Eastern Asia and was first recorded in Ireland (Waterford estuary) in 2005,
although viable populations never established in Irish rivers (J. Caffrey
pers. comm.). It has the potential to cause significant economic and
environmental damage where it becomes established (Clark et al. 1998).
Migrating upstream from breeding grounds in brackish water, these large
crabs can alter the morphological features of rivers and increase the
amount of fine sediment in the watercourse through their burrowing
activity, resulting in a threat to riverbank stability and land loss (Rosewarne
et al. 2016). This species predates voraciously on a wide variety of aquatic
invertebrates and fish eggs, and could outcompete native invertebrates (e.g.
white-clawed crayfish) for food and resources. (Schrimpf et al. 2014).
Floating pennywort (Hydrocotyle ranunculoides) is an aquatic plant that
is native to north America but naturalized in South America and parts of
Africa. It was first recorded in Britain in the 1980s and is now widespread
there, causing significant problems in infested watercourses, where it forms
extensive floating carpets on the surface of the water (Ruiz-Avila and
Klemm 1996). Its distribution in Ireland is very limited, having been
recorded at four sites, mainly artificial ponds in Northern Ireland in the
early 2000s (first record in 2002). Management programmes at all four
sites significantly reduced the populations of this highly invasive species.
H. ranunculoides was included in this exercise because of the fact that all
known populations in the island are confined to isolated ponds. It has not
yet appeared to be self-sustaining in the wild. Because of the biomass of
vegetation produced, this species can cause significant flood risks in affected
waters, while also adversely impacting native biodiversity, navigation and
water-based amenity use of these aquatic resources (Newman and Duenas
Quagga mussel (Dreissena rostriformis bugensis) was discovered in Great
Britain shortly after its nomination as the number one IAS in the GB
horizon scan (Roy et al. 2014). Its presence in GB increases the probability
of this species arriving here. Quagga mussel are ecosystem engineers in the
same genus as the zebra mussel (Dreissena polymorpha (Pallas, 1771)),
which has caused many biological impacts since arriving and establishing
in Irish waters in the early 1990s (Minchin et al. 2005; Lucyand Panov
2014). Quagga mussel have been spreading widely in both Europe and
North America (Karatayev et al. 2014; Aldridge et al. 2014) in recent years.
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While the zebra mussel is restricted to benthic habitats with hard
substrates, the quagga mussel can also settle on muddy benthos and in
invaded waters it commonly outcompetes zebra mussels and becomes the
dominant benthic organism in the soft sediments of lake systems (Sousa et
al. 2009; Karatayev et al. 2014). Zebra mussel are known to spread
effectively between and within countries attached (via byssal threads) to
leisure craft moved between waterways (Minchin et al. 2005; Padilla et al.
1996) and it is expected that this may be an effective vector for the spread
of quagga mussel, if it arrives to the island of Ireland.
Marine species ranked in Ireland’s horizon scan include pom-pom weed
(Caulacanthus okamurae), a turf-forming dark purple to brown, profusely
and irregularly branched alga with a hornlike appearance at branched tips.
It does not generally grow longer than 30 mm and is attached to the
substrate by creeping stolons. It generally occupies rocky, intertidal and
exposed habitats. Caulacanthus okamurae was introduced from Asia to
southern California in 1999 and has since been recorded in France and SW
Britain. Caulacanthus appears to displace macro-invertebrates, such as
barnacles, limpets, and periwinkles, in the high intertidal zone while
facilitating a more diverse array of small invertebrates and macroalgae
(Smith et al. 2014). This is likely due to the formation of a turf habitat in
the upper zone where turfs are uncommon.
The warm water barnacle (Hesperibalanus fallax) (Broch, 1927) is a
warm water sessile thoracican barnacle native to most of West Africa,
Morocco and Algeria (see Southward 2008 for identification details). With
one exception, H. fallax was unrecorded in Europe before 1980, but has
since been recorded in SW England, Wales, the Iberian peninsula, the
Atlantic and English Channel coast of France, in the Southern North Sea,
and in Guernsey (Southward et al. 2004). Its habitat ranges from 15 to 220
m depth and it can occur on a range of biological and man-made substrata,
but not on rocks or harbour walls (Southward et al. 2004). Its occurrence
on the seafan (Eucinella verrucosa (Pallas, 1766)) may adversely impact
populations and there is concern that H. fallax might become a serious
fouler of fish cages and other mariculture structures (Southward et al. 2004).
The terrestrial species ranked in this horizon scan are taxonomically
diverse. The most prevalent species on the short-list for consideration were
mammals (28), plants (23), insects (18), birds (10), amphibians (5),
lepidoptera (5) and invertebtrates (4). The terrestrial vertebrates (birds and
mammals) may be responsible for the greatest range of impacts on
biodiversity (Vilá et al. 2009). Roe deer (Capreolus capreolus) was heavily
debated when nominated as the highest risk species from the terrestrial
group. Previously introduced breeding populations of roe deer (in Lissadell
Estate and environs, Co. Sligo) were eradicated in circa 1905 (Stokes et al.
2006b). Roe deer are currently held in captivity in Wicklow and have
produced young in the last five years (J. Dick pers. obs.; NPWS pers. obs.).
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They are native to, and very widespread in GB, with their range expanding
by a compound rate of 2.3% between 1972 and 2002 (Ward 2005). The
similarity between habitat type in Great Britain and Ireland implies that
they would be equally successful here. Further, new, less stressful forms of
sedation for deer are now available, increasing the risk that deliberate
introductions of this species for hunting purposes could occur by transport
on boats, a known pathway of introduction for farmed deer species (such
as red and fallow).
Sacred ibis, (Threskiornis aethiopicus (Latham, 1790)), a large wading
bird native to Africa but commonly maintained in collections in GB, is
known to prey opportunistically on birds, fish, amphibians and invertebrates,
with high impacts on biodiversity (Baker and Hills 2008). It is most likely
to arrive here by natural dispersal, making the design and implementation
of preventative measures particularly challenging. T. aethiopicus is listed as
a Species of Union Concern.
Three insects (Agrilus planipennis Fairmaire, 1888, A. anxius Gory, 1841
and Hylastes ater Paykull, 1800) ranked in the horizon scan can potentially
enter Ireland as transport contaminants on plants or firewood, or alternatively
as escapees from the horticulture or ornamental plant imports. All three
are considered to be a significant threat to the diversity of native birch
(Betula species) and ash trees (Fraxinus excelsior L.) in European countries
at risk of invasion (Petter et al. 2020).
Identification and prioritisation of pathways are long standing key tenets
for minimising the introduction of IAS (COP 6 Decision VI/23; UNEP/
CBD/SBSTTA/18/9/Add.1; EU IAS regulation (EU 2014; Roy et al. 2014).
However, establishing the real or possible pathways for IAS can be a
challenge, even when assessing post-invasion (Roy et al. 2014). A review by
Essl et al. (2015) indicated that throughout Europe, many invader
pathways, particularly for freshwater and terrestrial species, remain unknown.
Species can arrive via more than one pathway, making it difficult to assess
the likelihood of arrival (Hulme 2009). Given that successful establishment
often requires multiple introductions of an invader (Kolar and Lodge 2001)
and that many factors including changing socioeconomics may affect the
dissemination of propagules to new regions (Wilson et al. 2009; Essl et al.
2015), there are complex challenges in terms of pathway identification and
subsequent management priorities. A major challenge in pathway prediction
is an effective quantitative assessment of the risk posed (Pyšek et al. 2011;
Essl et al. 2015). In the GB IAS horizon scan, Roy et al. (2014) predicted
that the stowaway pathway (on land, air, or sea transport vehicles) is likely
to be the most common mechanism of introduction but also predicted that
multiple pathways of introduction are likely. Results from the current
study indicate that multiple pathways exist for some species, indicating
that more than one management measure will probably be necessary for
prevention of each species. However, even in cases where there may be
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Lucy et al. (2020), Management of Biological Invasions 11(2): 155–177, 171
only one pathway, management is not always implemented. Four of the
species on this horizon scan list are named on the EU IAS regulation
(signal crayfish, floating pennywort, topmouth gudgeon and spiny cheek
crayfish), requiring both jurisdictions to manage their prevention and spread.
The range of pathways for the 40 named IAS across the three environments
calls for a diversity of prevention and management measures. These include
effective risk assessment, improved detection, recording and inspection at
ports and airports, full implementation of the Habitats Regulation in the ROI
(EC 2011) and the Wildlife and Natural Environment Act (Northern Ireland)
(NI 2011, 2019), to include management of trade including internet trade.
International agreements (e.g. the International Maritime Organisation’s
ballast water agreement) have effected a positive change in governance in
terms of marine pathways. However, as long as there are ships that are
equipped with ballast water tanks, there is no guarantee that ballast water
will not be discharged and act as a pathway for spread of marine IAS.
Codes of practice for pathways and IAS, similar to Check-Clean-Dry, need
to be developed and promoted, and more training and citizen science
events are needed to reach all ages and sectors in society. Knowledge
exchange between scientists, practitioners and policy makers must be
encouraged to improve channels of communication and thus improve
understanding of individual roles and develop a co-ordinated approach to
IAS management (Davis et al. 2018; Caffrey et al. 2014). This need for
improved communication has been recognised by the establishment of
Alien CSI COST Action programmes (Alien CSI 2020) and an upcoming
EU project on Communication and Understanding of IAS (EU 2020).
The need for biosecurity to prevent introductions and spread of IAS has
been emphasised in the literature (Caffrey et al. 2014 and references
therein) but has been limited in terms of implementation across on the
island of Ireland. One of the few consistent and coordinated biosecurity
campaigns mounted in Ireland was in 2002, which resulted when Foot and
Mouth disease threatened the country’s livestock and economy. This
coordinated response to a significant threat was successful and should
serve as an example of what can be achieved if there is a will and
determination to stop the introduction and spread of harmful organisms.
Since 2002, there has been no coordinated approach to biosecurity targeted
against IAS on the island of Ireland, a consequence of which has been the
continued introduction and spread of IAS on the island. Coordinated and
informed biosecurity against IAS that are already present in Ireland and
those identified horizon scan species determined during the current study
is paramount if biodiversity, human health and the economy are to be
protected. Best practice as operated in New Zealand and Australia must be
adopted and implemented here if we are to stop the IAS on the horizon
scan list from gaining entry to the island of Ireland.
In terms of the changing political landscape, new UK IAS legislation has
been prepared in advance of Britain’s exit from the EU. This legislation is
Horizon scan of invasive alien species for the island of Ireland
Lucy et al. (2020), Management of Biological Invasions 11(2): 155–177, 172
fully in line with the EU IAS regulation (EU 2014) and provides a degree of
legal assurance. However, there are new shipping routes opening (e.g. a
new freight shipping route from Waterford to Rotterdam opened in July
2019, described as a new pathway between Ireland and the continent),
which “could help exporters post-Brexit”. Such new routes could open
further pathways, allowing freshwater, marine and terrestrial invaders
identified in this horizon scan (among others) to be introduced to and
spread throughout the island of Ireland.
This horizon scan provides an important tool for IAS management on the
island of Ireland. Biosecurity efforts can be efficiently targeted to prevent
the introduction and spread of these listed IAS species in both jurisdictions,
maximising the resources available. The list also provides a focus for
education and outreach programmes for communities and citizen science.
Four of the species predicted to arrive, establish and spread in the next ten
years are included in the EU IAS Regulation. As the process of identifying
the 40 top IAS in this all-Ireland horizon scanning exercise was the consensual
decision of experts throughout the island, it is recommended that it is used
as a resource for subsequent risk assessments and for prioritisation of IAS
management in both Northern Ireland and in the Republic of Ireland.
The authors would like to thank the editors and reviewers for their helpful feedback and their
support in bringing this article to publication. We also thank the respective organisations of all
this manuscript’s authors (named as their affiliations) for supporting this horizon scan of
invasive alien species for the island of Ireland. Thanks also to Pia Bradler, a visiting scholar
from Leuphana University of Lüneburg, Germany for help with formatting the species lists.
Funding declaration
This horizon scan was undertaken as part of a project on the prevention, control and eradication
of invasive alien species. This project (2015-NC-MS-4) is funded under the EPA Research
Programme 2014-2020) and is a collaboration between the Institute of Technology, Sligo,
Queens University Belfast, and INVAS Biosecurity, Dublin. The EPA Research Programme is
a Government of Ireland initiative funded by the Department of Communications, Climate
Action and Environment. It is administered by the Environmental Protection Agency, which has
the statutory function of co-ordinating and promoting environmental research. HER was
supported by the Natural Environment Research Council award number NE/R016429/1 as part
of the UK-SCAPE programme delivering National Capability. RO would like to acknowledge
funding from the BLUEFISH project (INTERREG-funded; grant agreement no. 80991).
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Supplementary material
The following supplementary material is available for this article:
Table S1. Terrestrial species considered in session by expert group.
Table S2. Freshwater species considered in session by expert group.
Table S3. Marine species considered in session by expert group.
Appendix 1. Top Ten Species Profiles.
This material is available as part of online article from:
... The goal of horizon scanning in conservation science is to preemptively identify threats so researchers can provide timely and informed input on policy and decision-making (Sutherland and Woodroof 2009). In Europe, horizon scanning of emerging invaders has involved acquiring lists of potentially invasive species for a specific region, assessing the likelihood of arrival, establishment, and impact for each species, and, in some cases, building consensus among experts around a list of species ranked by risk (Parrott et al. 2009;Matthews et al. 2014;Roy et al. 2014;Gallardo et al. 2016;Lucy et al. 2020). These horizon scans have informed policy and guided resource allocation towards research and prevention efforts. ...
... This horizon scan of invasive plant threats to Florida provides a first step in reducing the impacts of invasive species on Florida's natural systems. Like other horizon scans of potential invasive species, the generated list informs future research efforts and policy (e.g., Matthews et al. 2014;Roy et al. 2014;Gallardo et al. 2016;Lucy et al. 2020). Our horizon scan builds on previous invasive species horizon scans, however, in important ways. ...
... material 1, Kendig et al. 2022) and could be used for other horizon scans of potential invasive plants. Second, the rapid risk assessments and peer reviews led to enough consensus among experts that our final rankings relied entirely on scores from that process (e.g., in contrast to Roy et al. 2014;Lucy et al. 2020). Consensus building led to important methodological changes (i.e., removing a taxon with too much uncertainty, revisiting assessments with arrival and establishment rubrics), but did not directly alter the rankings. ...
Full-text available
Early detection and eradication of invasive plants are more cost-effective than managing well-established invasive plant populations and their impacts. However, there is high uncertainty around which taxa are likely to become invasive in a given area. Horizon scanning that combines a data-driven approach with rapid risk assessment and consensus building among experts can help identify invasion threats. We performed a horizon scan of potential invasive plant threats to Florida, USA—a state with a high influx of introduced species, conditions that are generally favorable for plant establishment, and a history of negative impacts from invasive plants. We began with an initial list of 2128 non-native plant taxa that are known invaders or crop pests. We built on previous invasive species horizon scans by developing data-based criteria to prioritize 100 taxa for rapid risk assessment. The semi-automated prioritization process included selecting taxa “on the horizon” (i.e., not yet in the target location and not on a noxious weed list) with climate matching, naturalization history, “weediness” record, and global commonness. We derived overall invasion risk scores with rapid risk assessment by evaluating the likelihood of each of the taxa arriving, establishing, and having an impact in Florida. Then, following a consensus-building discussion, we identified six plant taxa as high risk, with overall risk scores ranging from 75 to 100 out of a possible 125. The six taxa are globally distributed, easily transported to new areas, found in regions with climates similar to Florida’s, and can impact native plant communities, human health, or agriculture. Finally, we evaluated our initial and final lists for potential biases. Assessors tended to assign higher risk scores to taxa that had more available information. In addition, we identified biases towards four plant families and certain geographical regions of origin. Our horizon scan approach identified taxa conforming to metrics of high invasion risk and used a methodology refined for plants that can be applied to other locations.
... Ship tracking has provided a mechanism by which to identify likely routes of invasion, particularly after the introduction of the Automatic Identification System in 2004 (O'Brien et al., 2017). Understanding shipping routes can facilitate horizon scanning; the process applied to invasive species management by prioritising the threats posed by potential invasives (Roy et al., 2014;Lucy et al., 2020). Targeted 'next pest' surveys are increasingly being utilised to design monitoring surveys, for species identified in horizon scanning exercises as those most likely to establish in the near future and cause deleterious impacts (Bishop and Hutchings, 2011). ...
... Focal invasive species for this study were selected based on a recently published horizon scanning exercise conducted for the island of Ireland which identified the likely invasive species across freshwater, marine and terrestrial realms (Lucy et al., 2020). The marine species selected were: the American razor clam Ensis leei (directus), the Asian shore crab Hemigrapsus sanguineus (which may already be present), the Brush clawed shore crab Hemigrapsus takanoi and the Chinese mitten crab Eriocheir sinensis. ...
... The American slipper limpet Crepidula fornicata was also investigated, as it is already present in Belfast Lough, Northern Ireland with sporadic sightings in the Republic of Ireland (Guy et al., 2013;Biodiversity Ireland, 2021). These species are invasive across European coastlines and use vessels, along with aquaculture gear, as vectors of invasion (Lucy et al., 2020). Their impacts on commercial activities, particularly mariculture, and interactions with parasites are detailed in Table 2. Invasive hostparasite interactions were also documented, due the possibility of coinvasions and interactions between invasive hosts, parasites and native communities. ...
Global shipping facilitates the introduction of invasive species and parasites via ballast water and hull fouling. Regional management of invasives may be strengthened by identifying the major routes in a network, to allow for targeted ship inspections. This study used cargo shipping records to establish the connectivity of shipping routes between ports in Ireland and other nations. 9291 records were analysed, investigating vessel residence and journey times. On average, vessels spent up to five days in port and less than five days at sea. However, there was strong variation, with general cargo ships recording up to 13 days in port. A horizon scan for species likely to invade in Ireland was incorporated for five species and their associated parasites: American razor clam, Asian shore crab, Brush clawed shore crab, Chinese mitten crab and American slipper limpet. Routes of concern are highlighted and a general framework for effective management is outlined.
... By contrast, an indirect climate change risk is associated with the wider group of INNS that are introduced by human agency and for which a favourable climate then further supports establishment and spread in the UK; this may occur throughout the UK and from throughout the globe (temperate Asia is a notable source of concern). A general description of risks from INNS in the UK is provided for Risk N2 as informed by reports on existing threats from the GB Non-native Species Secretariat and horizon-scanning activities carried out for both GB (Roy et al., 2014a), Ireland (Lucy et al., 2020), and Europe that evaluate potential threats that may materialise in the next few years. ...
... An expert horizon scan of the likelihood of arrival, establishment/spread and impact on biodiversity of INNS found that of the top potentially most important INNS for Great Britain five (out of 30) were freshwater (Roy et al., 2014a). For the island of Ireland 18 of the top 40 were freshwater species, with the signal crayfish in the top place, killer shrimp in third place and the salmon fluke (Gyrodactylus salaris), which can cause serious disease in salmon, trout and some other freshwater fish, in fifth place (Lucy et al., 2020). It is also in the top 30 for Great Britain. ...
... More recently, an expert-based horizon scan of invasive alien species has been completed for the island of Ireland (Lucy et al., 2020), finding that crustacean species (freshwater and marine) were the taxa most commonly identified as a threat due to their multiple pathways of introduction, their ability to act as ecosystem engineers and their resulting high impacts on biodiversity. The most likely marine invader was identified as warm-water barnacle (Hesperibalanus fallax), with pom-pom weed (Caulacanthus okamurae), American razor-clam (Ensis leei), Brush-clawed shore crab (Hemigrapsus takanoi), the sponge Celtodoryx ciocalyptoides, and Asian shore crab (Hemigrapsus sanguineus) also identified in the top 40 overall threats. ...
Technical Report
Full-text available
The CCRA is a comprehensive assessment of the risks to the UK from climate change, as required by Act of Parliament every 5 years (Climate Change Act)
... Many approaches have been implemented to reduce or quantify the bias associated with expert-elicitation methods, including Delphi techniques (Mukherjee et al., 2015). Horizon scanning has been used specifically within the context of biological invasions to rank research priorities (Gallardo et al., 2016), develop risk assessment protocols (Roy et al., 2020), inform prevention (Lucy et al., 2020;Tsiamis et al., 2020), and management (Booy et al., 2017). ...
Full-text available
Invasive alien species (IAS) are a rising threat to biodiversity, national security, and regional economies, with impacts in the hundreds of billions of U.S. dollars annually. Proactive or predictive approaches guided by scientific knowledge are essential to keeping pace with growing impacts of invasions under climate change. Although the rapid development of diverse technologies and approaches has produced tools with the potential to greatly accelerate invasion research and management, innovation has far outpaced implementation and coordination. Technological and methodological syntheses are urgently needed to close the growing implementation gap and facilitate interdisciplinary collaboration and synergy among evolving disciplines. A broad review is necessary to demonstrate the utility and relevance of work in diverse fields to generate actionable science for the ongoing invasion crisis. Here, we review such advances in relevant fields including remote sensing, epidemiology, big data analytics, environmental DNA (eDNA) sampling, genomics, and others, and present a generalized framework for distilling existing and emerging data into products for proactive IAS research and management. This integrated workflow provides a pathway for scientists and practitioners in diverse disciplines to contribute to applied invasion biology in a coordinated, synergistic, and scalable manner.
... In a recent horizon scan of impacting species likely to arrive in Ireland, D. rostriformis bugensis was considered a high-risk invader (Lucy et al. 2020). This follows a horizon scan for Britain (Roy et al. 2014) which also considered this species to be of high risk. ...
... Anticipating future challenges and opportunities is paramount for adequate strategy development, policy making, risk management, threat identification, and research prioritization in invasion science (Ricciardi et al., 2017). Several studies have been conducted to anticipate future invasion processes and their risks (e.g., Gallardo et al., 2016;Roy et al., 2019;Hughes et al., 2020;Lucy et al., 2020), and thereby pinpoint future monitoring and management measures toward invasive species (e.g., Matlack, 2002;Robertson et al., 2003;Booy et al., 2020). ...
... Effective management strategies are underpinned by communication and outreach to policy makers, stakeholders and the public which improve awareness of-and then actions against-the most impactful invasive species (Courchamp et al. 2017;Lucy et al. 2020). Two decades ago, in response to a lack of specific targets to motivate policy makers and raise public awareness of invasive species, a list of 100 high profile species was compiled by the International Union for the Conservation of Nature (IUCN) Invasive Species Specialist Group (ISSG) of the Species Survival Commission. ...
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Biological invasions are increasing worldwide , damaging ecosystems and socioeconomic sectors. Two decades ago, the ''100 of the world's worst'' invasive alien species list was established by the IUCN to improve communications , identifying particularly damaging 'flagship' invaders globally (hereafter, worst). Whilst this list has bolstered invader awareness , whether worst species are especially economically damaging and how they compare to other invaders (hereafter, other) remain unknown. Here, we quantify invasion costs using the most comprehensive global database compiling them (InvaCost). We compare these costs between worst and other species against sectorial, taxonomic and regional descriptors, and examine temporal cost trends. Only 60 of the 100 worst species had invasion costs considered as highly reliable and actually observed estimates (median: US$ 43 million). On average, these costs were significantly higher than the 463 other invasive species recorded in InvaCost (median: US$ 0.53 million), although some other species had higher costs than most worst species. Damages to the environment from the worst species dominated, whereas other species largely impacted agriculture. Disproportionately highest worst species costs were incurred in North America, whilst costs were more evenly distributed for other species; animal invasions were always costliest. Proportional management expenditures were low for the other species, and surprisingly, over twice as low for the worst species.
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The introduction of non‐native species to new locations is a growing global phenomenon with major negative effects on native species and biodiversity. Such introductions potentially bring competitors into contact leading to partial or total species replacements. This creates an opportunity to study novel species interactions as they occur, with the potential to address the strength of inter‐ and intraspecific interactions, most notably competition. Such potential has often not been realized, however, due to the difficulties inherent in detecting rapid and spatially expansive species interactions under natural field conditions. The invasive amphipod crustacean Gammarus pulex has replaced a native species, Gammarus duebeni celticus, in river and lake systems across Europe. This replacement process is at least partially driven by differential parasitism, cannibalism, and intraguild predation, but the role of interspecific competition has yet to be resolved. Here, we examine how abundance of an invasive species may affect spatial niche breadth of a native congeneric species. We base our analyses of niche breadth on ordination and factor analysis of biological community and physical parameters, respectively, constituting a summative, multidimensional approach to niche breadth along environmental gradients. Results derived from biological and environmental niche criteria were consistent, although interspecific effects were stronger using the biological niche approach. We show that the niche breadth of the native species is constrained as abundance of the invader increases, but the converse effect does not occur. We conclude that the interaction between invasive G. pulex and native G. d. celticus under natural conditions is consistent with strong interspecific competition whereby a native, weaker competitor is replaced by a superior invasive competitor. This study indicates a strong role of interspecific competition, alongside other known interactions such as differential intraguild predation, in rapid and expansive species replacements following biological invasions. Niche shift may occur generally at an early stage in species replacements of native by an invasive species, as a result of a competitive processes leading to the eventual demise of a weaker competitor faced with a novel, invasive species.
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Despite voluminous literature identifying the impacts of invasive species, summaries of monetary costs for some taxonomic groups remain limited. Invasive alien crustaceans often have profound impacts on recipient ecosystems, but there may be great unknowns related to their economic costs. Using the InvaCost database, we quantify and analyse reported costs associated with invasive crustaceans globally across taxonomic, spatial, and temporal descriptors. Specifically, we quantify the costs of prominent aquatic crustaceans — crayfish, crabs, amphipods, and lobsters. Between 2000 and 2020, crayfish caused US$ 120.5 million in reported costs; the vast majority (99%) being attributed to representatives of Astacidae and Cambaridae. Crayfish-related costs were unevenly distributed across countries, with a strong bias towards European economies (US$ 116.4 million; mainly due to the signal crayfish in Sweden), followed by costs reported from North America and Asia. The costs were also largely predicted or extrapolated, and thus not based on empirical observations. Despite these limitations, the costs of invasive crayfish have increased considerably over the past two decades, averaging US$ 5.7 million per year. Invasive crabs have caused costs of US$ 150.2 million since 1960 and the ratios were again uneven (57% in North America and 42% in Europe). Damage-related costs dominated for both crayfish (80%) and crabs (99%), with management costs lacking or even more under-reported. Reported costs for invasive amphipods (US$ 178.8 thousand) and lobsters (US$ 44.6 thousand) were considerably lower, suggesting a lack of effort in reporting costs for these groups or effects that are largely non-monetised. Despite the well-known damage caused by invasive crustaceans, we identify data limitations that prevent a full accounting of the economic costs of these invasive groups, while highlighting the increasing costs at several scales based on the available literature. Further cost reports are needed to better assess the true magnitude of monetary costs caused by invasive aquatic crustaceans.
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We report the presence of the North American Crangonyx floridanus co-occurring with C. pseudogracilis in two Irish rivers, following surveys in three rivers, eleven lake sites and an ornamental pond in 2020. This is the first record of C. floridanus in Ireland which was previously recorded in Britain in 2017. We predict that this species is likely to expand its range through the river and canal connections in Ireland as well as from inadvertent anthropogenic transmission. The taxonomic criteria are cryptic and for this reason, we used genetic methods to distinguish the two species in this study. The results highlight the need to investigate the distribution and impact of these two species in freshwater habitats in Ireland.
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Invasive alien species (IAS) are one of the major drivers of change that can negatively affect biodiversity, ecosystem functions and services and human health; islands are particularly vulnerable to biological invasions. Horizon scanning can lead to prioritisation of IAS to inform decision-making and action; its scale and scope can vary depending on the need. We focussed on IAS likely to arrive, establish and affect biodiversity and human health on the Mediterranean island of Cyprus. The scope of the horizon scanning was the entire island of Cyprus. We used a two-step consensus-building process in which experts reviewed and scored lists of alien species on their likelihood of arrival, establishment and potential to affect biodiversity, ecosystems and/or human health in the next 10 years. We reviewed 225 alien species, considered to be currently absent on Cyprus, across taxa and environments. We agreed upon 100 species that constituted very high, high or medium biodiversity risk, often arriving through multiple pathways of introduction. The remaining 125 species were ranked as low risk. The potential impacts on human health were documented for all 225 species; 82 species were considered to have a potentially negative impact on human health ranging from nuisance to disease transmission. The scope of the horizon scanning was the entire island of Cyprus, but the thematic groups also considered the relevance of the top 100 species to the Sovereign Base Areas of Cyprus, given their differing governance. This horizon scan provides the first systematic exercise to identify invasive alien species of potential concern to biodiversity and ecosystems but also human health within the Mediterranean region. The process and outcomes should provide other islands in the region and beyond with baseline data to improve IAS prioritisation and management.
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Cherax destructor is a crayfish endemic to southeastern Australia and one of the last alien crayfish to be introduced in Italy. In the Laghi di Ninfa Natural Reserve (Latium region, Central Italy), the species was probably introduced in 1999, but only reported for the first time in 2008. Nearby this area, the most widespread alien crayfish is the red swamp crayfish Procambarus clarkii. In the Natural Reserve, between 2008 and 2013 and during spring and summer, crayfish sampling was carried out with baited traps to assess the distribution of C. destructor and its possible relationship with P. clarkii. Cherax destructor was first recorded in 2008; few P. clarkii were detected in the cultivation ponds where C. destructor was present in 2012 and 2013. Moreover, crayfish plague analyses evidenced a positive result in two out of the 12 sampled P. clarkii. Cherax destructor is now completely absent from the Natural Reserve, while P. clarkii has spread in the area and was probably responsible for this eradication since C. destructor is vulnerable to crayfish plague which was also detected in the area. An ecosystem restoration project in the area favoured the spread of. P. clarkii; the implications of this intervention are discussed.
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Outreach is an important element of scientific communication and a prescribed element of many projects, but few scientists have training in communications. This paper describes the outreach element of a project on invasive alien species. A communications plan was drawn up to streamline communications efforts, allowing us to take advantage of unanticipated opportunities to engage with the public, while still maintaining the desired focus, using minimal resources. Here, we use two simple metrics—“passive reach” and “interactions”—to measure the extent and the intensity of communications, and we also look at the advantages and limitations provided by different media. Broadcast media and social media have the capacity to reach a wide audience, but have a low percentage of interaction. Workshops and citizen science events tend to reach a much smaller audience, but generate greater levels of engagement. Understanding these dynamics is important in designing an effective communications plan, which uses the minimum number of resources to generate maximum impact. Building the credibility of the researcher or the project means that your research will reach a wider audience, and your message is more likely to have an impact.
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Freshwaters are subject to particularly high rates of species introductions; hence, invaders increasingly co-occur and may interact to enhance impacts on ecosystem structure and function. As trophic interactions are a key mechanism by which invaders influence communities, we used a combination of approaches to investigate the feeding preferences and community impacts of two globally invasive large benthic decapods that co-occur in freshwaters: the signal crayfish (Pacifastacus leniusculus) and Chinese mitten crab (Eriocheir sinensis). In laboratory preference tests, both consumed similar food items, including chironomids, isopods and the eggs of two coarse fish species. In a comparison of predatory functional responses with a native crayfish (Austropotamobius pallipes), juvenile E. sinensis had a greater predatory intensity than the native A. pallipes on the keystone shredder Gammarus pulex, and also displayed a greater preference than P. leniusculus for this prey item. In outdoor mesocosms (n = 16) used to investigate community impacts, the abundance of amphipods, isopods, chironomids and gastropods declined in the presence of decapods, and a decapod >gastropod >periphyton trophic cascade was detected when both species were present. Eriocheir sinensis affected a wider range of animal taxa than P. leniusculus. Stable-isotope and gut-content analysis of wild-caught adult specimens of both invaders revealed a wide and overlapping range of diet items including macrophytes, algae, terrestrial detritus, macroinvertebrates and fish. Both decapods were similarly enriched in 15N and occupied the same trophic level as Ephemeroptera, Odonata and Notonecta. Eriocheir sinensis δ13C values were closely aligned with macrophytes indicating a reliance on energy from this basal resource, supported by evidence of direct consumption from gut contents. Pacifastacus leniusculus δ13C values were intermediate between those of terrestrial leaf litter and macrophytes, suggesting reliance on both allochthonous and autochthonous energy pathways. Our results suggest that E. sinensis is likely to exert a greater per capita impact on the macroinvertebrate communities in invaded systems than P. leniusculus, with potential indirect effects on productivity and energy flow through the community.
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The spreading of new crayfish species poses a serious risk for freshwater ecosystems; because they are omnivores they influence more than one level in the trophic chain and they represent a significant part of the benthic biomass. Both the environmental change through global warming and the expansion of the pet trade increase the possibilities of their spreading. We investigated the potential of four " warm water " highly invasive crayfish species to overwinter in the temperate zone, so as to predict whether these species pose a risk for European freshwaters. We used 15 specimens of each of the following species: the red swamp crayfish (Procambarus clarkii), the marbled crayfish (Procambarus fallax f. virginalis), the yabby (Cherax destructor), and the redclaw (Cherax quadricarinatus). Specimens were acclimatized and kept for 6.5 months at temperatures simulating the winter temperature regime of European temperate zone lentic ecosystems. We conclude that the red swamp crayfish, marbled crayfish and yabby have the ability to withstand low winter temperatures relevant for lentic habitats in the European temperate zone, making them a serious invasive threat to freshwater ecosystems.
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Substantial progress has been made in understanding how pathways underlie and mediate biological invasions. However, key features of their role in invasions remain poorly understood, available knowledge is widely scattered, and major frontiers in research and management are insufficiently characterized. We review the state of the art, highlight recent advances, identify pitfalls and constraints, and discuss major challenges in four broad fields of pathway research and management: pathway classification, application of pathway information, management response, and management impact. We present approaches to describe and quantify pathway attributes (e.g., spatiotemporal changes, proxies of introduction effort, environmental and socioeconomic contexts) and how they interact with species traits and regional characteristics. We also provide recommendations for a research agenda with particular focus on emerging (or neglected) research questions and present new analytical tools in the context of pathway research and management.
To disperse between isolated waterbodies, freshwater organisms must often cross terrestrial barriers and many freshwater animals that are incapable of flight must rely on transport via flooding events, other animals or anthropogenic activity. Decapods such as crayfish, on the other hand, can disperse to nearby waterbodies by walking on land, a behaviour that has facilitated the spread of invasive species. Overland movement could play a key role in the management of non-native crayfish, though to what extent terrestrial emigration occurs in different species is poorly understood. Here, we directly compared the terrestrial emigration tendency of two non-native crayfish species in Great Britain; red swamp (Procambarus clarkii) and signal (Pacifastacus leniusculus) crayfish. We found that both species emigrated from the water and that there was no significant difference in terms of their terrestrial emigration tendency, suggesting that there is a risk both of these species will migrate overland and disperse to new habitats. This study shows that terrestrial emigration is an important behavioural trait to consider when preventing the escape of crayfish from aquaculture and further spread of invasive species.
Species translocation leads to disease emergence in native species of considerable economic importance. Generalist parasites are more likely to be transported, become established and infect new hosts, thus their risk needs to be evaluated. Freshwater systems are particularly at risk from parasite introductions due to the frequency of fish movements, lack of international legislative controls for non-listed pathogens and inherent difficulties with monitoring disease introductions in wild fish populations. Here we used one of the world's most invasive freshwater fish, the topmouth gudegon, Pseudorasbora parva, to demonstrate the risk posed by an emergent generalist parasite, Sphaerothecum destruens. Pseudorasbora parva has spread to 32 countries from its native range in China through the aquaculture trade and has introduced S. destruens to at least five of these. We systematically investigated the spread of S. destruens through Great Britain and its establishment in native fish communities through a combination of phylogenetic studies of the host and parasite and a novel environmental DNA detection assay. Molecular approaches confirmed that S. destruens is present in 50% of the P. parva communities tested and was also detected in resident native fish communities but in the absence of notable histopathological changes. We identified specific P. parva haplotypes associated with S. destruens and evaluated the risk of disease emergence from this cryptic fish parasite. We provide a framework that can be applied to any aquatic pathogen to enhance detection and help mitigate future disease risks in wild fish populations.
1. Predictions of the identities and ecological impacts of invasive alien species are critical for risk assessment, but presently we lack universal and standardized metrics that reliably predict the likelihood and degree of impact of such invaders (i.e. measurable changes in populations of affected species). This need is especially pressing for emerging and potential future invaders that have no invasion history. Such a metric would also ideally apply across diverse taxonomic and trophic groups. 2. We derive a new metric of invader ecological impact that blends: (i) the classic Functional Response (FR; consumer per capita effect) and Numerical Response (NR; consumer population response) approaches to determining consumer impact, that is, the Total Response (TR = FR × NR), with; (ii) the ‘Parker–Lonsdale equation’ for invader impact, where Impact = Range × Abundance × Effect (per capita effect), into; (iii) a new metric, Relative Impact Potential (RIP), where RIP = FR × Abundance. The RIP metric is an invader/native ratio, where values >1 predict that invader ecological impact will occur, and increasing values above 1 indicate increasing impact. In addition, the invader/invader RIP ratio allows comparisons of the ecological impacts of different invaders. 3. Across a diverse range of trophic and taxonomic groups, including predators, herbivores, animals and plants (22 invader/native systems with 47 individual comparisons), high-impact invaders were significantly associated with higher FRs compared to native trophic analogues. However, the RIP metric substantially improves this association, with 100% predictive power of high-impact invaders. 4. Further, RIP scores were significantly and positively correlated with two independent ecological impact scores for invaders, allowing prediction of the degree of impact of invasive alien species with the RIP metric. Finally, invader/invader RIP scores were also successful in identifying and associating with higher impacting invasive alien species. 5. Synthesis and applications. The Relative Impact Potential metric combines the per capita effects of invaders with their abundances, relative to trophically analogous natives, and is successful in predicting the likelihood and degree of ecological impact caused by invasive alien species. As the metric constitutes readily measurable features of individuals, populations and species across abiotic and biotic context-dependencies, even emerging and potential future invasive alien species can be assessed. The Relative Impact Potential metric can be rapidly utilized by scientists and practitioners and could inform policy and management of invasive alien species across diverse taxonomic and trophic groups.
The Ponto-Caspian amphipod, Dikerogammarus villosus is a recent and successful invader of the River Rhine. It has dispersed over large distances in a short time. As it has an extensive invasion history in Europe, it is thought to have potential to reach and invade the Great Lakes in America. However, for this it must survive the stress of high salinity during ballast water exchange. Therefore, several aspects of the general ecophysiology of D. villosus were studied by means of laboratory experiments. Highest oxygen consumption occurred around 20°C. This result is supported by the pleopod beat frequency measurements, showing a maximum around 20°C. Our results indicate that D. villosus has a wide temperature tolerance. Salinity tolerance experiments demonstrated that salinities of 25‰ and higher are lethal to D. villosus. However, D. villosus survived at salinities up to 10‰ and adapted to salinities of up to 20‰ within 10 days. Ballast water exchange will thus only act as an appropriate biocide against D. villosus, when salinities reach at least 25‰. These results indicate that D. villosus is an euryhaline, eurythermic species, similar to most immigrants inhabiting the River Rhine. By these capacities for adaptation D. villosus may be able to survive (incomplete) ballast water exchange and subsequently be dispersed over large distances by means of ballast water and to develop large populations in temperate areas on a global scale.