Capacity, capability and cross-border challenges associatedwith marine eradication programmes in Europe: The attemptederadication of an invasive non-native ascidian, Didemnumvexillum in Wales, United Kingdom

Katie Sambrook a,n, Rohan H.F. Holt b, Rowland Sharp b, Kate Griffith a, Ronan C. Roche a,Rebekah G. Newstead a, Gabrielle Wyn b, Stuart R. Jenkins a

a School of Ocean Sciences, Bangor University, Menai Bridge LL59 5AB, Anglesey, UKb Natural Resources Wales, Maes y Ffynnon, Ffordd Penrhos, Bangor LL57 2DN, UK

a r t i c l e i n f o

Article history:Received 17 December 2013Received in revised form7 March 2014Accepted 7 March 2014Available online 1 April 2014

Keywords:Didemnum vexillumEradicationMarine invasive speciesRapid responseBiosecurityControl

a b s t r a c t

Increasing recognition of the threat which invasive non-native species present to ecological andeconomic assets has led to a recent surge in international, regional and national policies. Within theEuropean Union, a draft EU Regulation on the prevention and management of invasive alien species hasbeen developed. The draft Regulation, published in 2013, recommends the creation of a list of invasivealien species of Union concern, wherein any Member State identifying newly establishing populations ofthese species must implement rapid eradication measures. The first recording of the invasive non-nativeascidian Didemnum vexillum in Britain in 2008 in Wales, and subsequent eradication efforts, presents atimely opportunity to evaluate the United Kingdom's existing capability and capacity to undertake arapid eradication in the marine environment in light of the draft EU Regulation, as well as highlightingsome of the cross-border challenges facing the EU. Although the UK is often cited within Europe ashaving made significant progress in the field of invasion management, the lessons learned from theeradication process in Wales highlight that the UK is inadequately prepared to undertake rapideradication measures in the marine environment and that the lack of a coordinated approach betweennations has significant potential to devalue localised eradication efforts. A number of measures arediscussed to enhance future capability both in the UK and the wider European Union including enhancedalerting mechanisms, science-based monitoring programmes to enable early detection, increasedcommitment of resources and the need for cross-border collaboration.

& 2014 Elsevier Ltd. All rights reserved.

1. Introduction

The continued expansion of global trade and transportationnetworks is facilitating the spread of non-native species on anunprecedented scale [1–4]. Although many established non-nativespecies are innocuous, a minority become invasive in their newenvironment with concomitant ecological, economic and socialimpacts [5–8]. One of the greatest threats associated with invasivenon-native species is the risk they present to patterns of biodi-versity [7]. At a local scale, colonisation by non-natives may havenegative consequences on native biota and, globally, the move-ment of species is resulting in disparate biogeographic regions

becoming progressively more homogenous [1,9–11]. Growingconcern around the effects of non-natives on biodiversity has ledto the management of non-native species gaining an increasinglyhigh profile in the political arena, with recent years witnessing asurge in the number of international, regional and nationalpolicies aimed at addressing the pathways of introduction andmitigating the adverse impacts associated with invasive non-native species [12–14].

Within the European Union (EU) it is widely acknowledged thata coordinated response is critical in order to tackle the cross-border issues associated with non-native species [4]. Recognisingthe current fragmented approach of Member States, the EU hascommitted to introducing a legislative instrument to ensurecomprehensive Member State engagement [15]. Recently pub-lished, the proposed draft EU Regulation [16] adheres to thethree-stage hierarchical approach advocated by the Convention

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Marine Policy

http://dx.doi.org/10.1016/j.marpol.2014.03.0180308-597X/& 2014 Elsevier Ltd. All rights reserved.

n Corresponding author. Tel.: þ44 7740 946004.E-mail address: katie.sambrook@hotmail.co.uk (K. Sambrook).

Marine Policy 48 (2014) 51–58

on Biological Diversity [17] of: 1) prevention 2) early detection andrapid response and 3) containment and long-term control. Inaddition, the draft Regulation recommends the establishment ofa priority list of invasive non-native species that pose the highestrisk to the biodiversity and economic stability of the EuropeanUnion, termed invasive alien species (IAS) of Union concern.Where a newly establishing population of an IAS of Union concernis detected by a Member State, the draft proposal indicates that theaffected State will be obligated to apply eradication measureswithin three months of notifying the Commission [16].

Although prevention, achieved by limiting the pathways ofintroduction, is universally agreed as the preferred option tomanage the introduction of non-native species, the high numberof pathways identified and open nature of the marine environ-ment makes controlling marine non-native introductions inher-ently challenging [18–21]. The adoption of preventative steps toaddress marine pathways has been slow [7], although the intro-duction of remedial measures such as the not yet ratified Interna-tional Maritime Organization's (IMO) International Convention forthe Control and Management of Ships’ Ballast Water and Sedi-ments (BWMC) [22], the IMO Guidelines for the Control andManagement of Ships’ Biofouling [23] and the EU Regulationconcerning the use of alien and locally absent species in aqua-culture [24] are positive signs of progress. However, significantgaps still remain, leaving even those nations with the mostadvanced biosecurity protocols unable to wholly prevent futureincursions [4,25,26]. In addition, once a marine non-native hasestablished in a novel environment, there are few mechanisms inplace to limit secondary spread. In the absence of a mandatoryregulatory framework to reduce incursions through rigorous path-way management, introductions of marine non-native speciescontinue apace, particularly in areas identified as invasion hot-spots such as estuaries, ports, marinas and aquaculture facilities[27–30]. A collective inability to prevent marine incursions meansthat for many nations, the development of robust early detectionand rapid response plans are becoming integral components ofinvasion management [19,26,31].

The finding of an invasive non-native ascidian, Didemnumvexillum Kott, 2002 in Wales [32] and the subsequent eradicationprogramme provides a valuable and timely opportunity to evalu-ate existing capacity and capability in the United Kingdom (UK) torapidly respond to a newly identified marine invasive non-nativespecies, particularly in the light of the proposed EU Regulation.This paper describes both the Welsh response to the D. vexilluminvasion and the management steps taken throughout Britain. Byreviewing these management actions, we hope to elucidate gapswithin the existing UK framework for managing marine invasivenon-native species and also illustrate some of the unique cross-border challenges facing Europe which isolated nations withadvanced biosecurity protocols, such as Australia and New Zeal-and, have not encountered.

2. Chronology of D. vexillum invasion

2.1. September 2008: discovery of an unknown ascidian

During August and September 2008, five marinas in NorthWales were surveyed for the presence of a targeted list of 11 non-native species known to have established populations in GreatBritain or Europe [32]. At Holyhead Marina, Anglesey, an unknowncolonial ascidian was found which closely matched morphologicaldescriptions of D. vexillum, an invasive species of temperatemarine waters which has rapidly expanded its global distributionsince the 1970s [33,34]. In addition to the morphology of adultcolonies, late stage unhatched larvae showed characteristics

considered diagnostic for D. vexillum and samples submitted to ataxonomic expert led to confirmation of the preliminary identifi-cation [32]. The finding of D. vexillum in Holyhead Marina, Waleswas the first official record of an established population in GreatBritain [35].

2.2. One month post-discovery: formation of a Wales working group

Following the discovery of the unknown ascidian in HolyheadMarina and prior to its formal identification as D. vexillum, theCountryside Council for Wales (CCW now Natural Resources Wales(NRW)), the Welsh Government's statutory advisor on natureconservation, was notified of the suspected incursion. In response,CCW formed a Wales working group with representatives fromgovernment, industry and academia to scope out managementoptions. The possible introduction of D. vexillum to Welsh inshorewaters was considered a serious threat to ecological and socio-economic assets based on its capacity for rapid growth in bothartificial (e.g. marinas and aquaculture sites) and natural environ-ments and its propensity to smother surrounding organisms[36–39]. From an ecological perspective, the Irish Sea has severalmarine Special Areas of Conservation (SACs) which, if altered as aconsequence of the spread of D. vexillum, could have significantimplications given the UK's obligations to maintain these sites in afavourable condition. Coastal waters around North Wales are alsoeconomically important, supporting regional fisheries includingthe UK's most productive mussel fishery [40]. With Holyheadserving as an important regional transport hub in the Irish Sea andthe inoculation source undetermined, the risk of finding additionalestablished populations was considered high [40].

2.3. Three to five months following discovery (December 2008 toFebruary 2009): delimitation surveys in Wales

Rapid assessment surveys at a further nine marinas acrossWales found no additional D. vexillum populations and a delimita-tion exercise at the site of the initial incursion showed that D.vexillum was confined to pontoons and mooring chains in Holy-head Marina with coverage ranging from o1% to 10% [35]. It wasnot found on the seabed and had not established within the widerharbour area. Colonies were encrusting and sheet-like, with noevidence of the pendulous growth forms reported from otherinvaded locations, implying its relatively recent establishment[41,42]. D. vexillum was observed fouling two recreational yachtswhich had been berthed in the marina for over a year, both ofwhich were removed from the water and cleaned [43]. Confine-ment of D. vexillum to Holyhead Marina indicated that the originalinoculation source was probably an infected vessel(s) visiting themarina. At this time, in Europe, populations of D. vexillum wereknown to have established in the Netherlands, France and the eastcoast of Ireland [35,42,44].

2.4. Seven months post-discovery (March 2009): feasibilityof eradication and/or control

The confinement of D. vexillum to Holyhead Marina, the limiteddispersal range of the larvae [45] and consensus that the invasionhad not yet reached the exponential growth stage [40] indicatedthat eradication was a viable option [21,46]. A combination of thepotential costs to the valuable shellfish industry in North Walesand the legal ramifications if the environmental status of themarine SACs were affected motivated the Wales working group tofocus on eradicating D. vexillum from Holyhead Marina.

Two eradication options were presented: 1) full eradication in2009 with follow up treatment for the next two years if required;and 2) trial eradication in 2009 followed by a full eradication

K. Sambrook et al. / Marine Policy 48 (2014) 51–5852

attempt in 2010, with additional treatment during the subsequentyear where necessary. Both options recommended complementarymonitoring programmes and awareness raising plus the introduc-tion of voluntary vector controls to reduce the risk of reinfection,an issue highlighted as a major concern that could devalue theeradication attempt [40]. Preliminary costs ranged from d350,000to d385,000 for the three-year eradication programme, signifi-cantly lower than the estimates for economic regional losses in theevent of further spread. Based on the inexperience of conductingmarine eradications in the UK, the second option of eradicationpilot followed by full-scale eradication was selected.

3. Eradication programme in Holyhead Marina

Commensurate with the economic and ecological threat posed byD. vexillum, theWelsh Government agreed in October 2009 to fund aneradication attempt, with CCW providing a dedicated staff member tomanage the project. By categorising the status of the D. vexilluminvasion as an ‘emergency’ within its risk register, CCW was able toexpedite procurement and contractual procedures enabling thecommencement of the pilot eradication during October 2009 [47].

Previous efforts in New Zealand to address a D. vexilluminvasion informed the basic eradication design [48]. All artificialstructures were encapsulated in reinforced PVC using bag, sheet ortubular designs thus restricting water flow depriving the targetedbiota of food and oxygen [37]. The efficacy of this biologicaltreatment is diminished by low water temperatures and inclementweather where overtopping of wrappings can reintroduce oxyge-nated water to the biota [47]. The winter eradication schedule,chosen because D. vexillum recruitment has been observed tocease at water temperatures between 9 1C and 11 1C [45], and theneed to re-use the limited materials on different parts of themarina necessitated the occasional application of a chemicalaccelerant to expedite the treatment process. Calcium hypochlor-ite was the preferred treatment for the bags and wrappings butsodium hypochlorite was used to spray boat hulls and mooringchains where wrapping was not possible.

The eradication pilot tested materials and methods on a subsetof artificial structures including pontoon fingers, walkway pon-toons, a large breakwater pontoon, chains and mooring buoys.Initial tests proved promising and a full-scale eradication beganearlier than originally planned in November 2009. Below is asummary of the eradication programme. More detailed informa-tion on the methodology can be found in Holt et al. [47].

3.1. 14 months post-discovery (November 2009): first full-scaleeradication

Due to resource limitations in terms of personnel and materials,treatments were staggered across the site extending the eradicationperiod over seven months from November 2009 to May 2010. A totalof 530 pontoon units were treated using customised bags designedto accommodate the different pontoon float designs around themarina [47]. In addition 110 moorings and 30 swinging mooringswere wrapped using either sheet or tubular 400–500 gsm polythenedispensed from a roll. Wraps were left for the duration of theprogramme (‘set-and-forget’), although this approach appeared to beeffective after 7–10 days as evidenced by the contents turning black[47]. One vessel found to be harbouring D. vexillum was dried out athigh water and treated with sodium hypochlorite.

3.2. 20 months following discovery: post-eradication survey

Initial results from a rapid assessment survey in May 2010indicated that the eradication attempt had successfully removed D.

vexillum from Holyhead Marina. Where any sign of D. vexillumremained, further investigation showed that the structural integ-rity of the animal had been lost and bacterial growth quicklycaused complete degradation. However, another survey in Sep-tember 2010 found that D. vexillum had re-established within themarina colonising 19% of the inner portion of the marina struc-tures. Further survey work in October 2010 revealed that 16 of the18 breakwater pontoons had also become recolonised, equating to50% of the total submerged surface area re-infected with D.vexillum colonies.

3.3. Reasons for low success rate

Recruitment of D. vexillum larvae to settlement panels inHolyhead Marina occurred continuously from the end of Julythrough to mid-December 2009, ceasing when the water tem-perature fell below 9 1C [49]. As the full-scale eradication com-menced in November 2009, there was a six-week window duringthe treatment period when larvae were still being released. Thusbecause of the staggered treatment of surfaces and the promptremoval of bags following treatment, there was a short period oftime when healthy D. vexillum colonies could potentially supplylarvae to recruit to treated surfaces.

3.4. Three years post-discovery: continued eradication work

Whilst the first full-scale eradication was not completelysuccessful, the eradication programme had been designed toaccommodate for additional follow up treatment [40]. However asecond eradication was not attempted until January 2012 owing todifficulty securing funding. The same methodology was used butenhanced by the provision of additional materials and the experi-ence gained during the first eradication. More structures weretreated concurrently and the eradication time was reduced fromseven months to three, with the bags and wraps removed duringMarch 2012. A survey in July 2012 showed 30 chains and twopontoons had small D. vexillum colonies and these areas, plusbuffer zones were re-treated, using calcium hypochlorite on thechains to increase the chances of success. Wraps were removed inSeptember 2012 but a further seven chains, 35 pontoons and aportion of plastic wrap used to encapsulate one of the chains werefound to be infected. Retreatment led to more promising results inNovember 2012 with small colonies of D. vexillum found in onlyfour locations in the marina which were re-treated in January2013. The most recent survey in September 2013 found smallcolonies on one of the breakwaters and efforts are ongoing to treatthis structure. Although eradication remains the primary goal ofthe programme, the continued reappearance of colonies has ledthe Wales working group to focus attention on longer-termcontainment and control options including improved biosecuritymeasures and further investigation into inoculation sources. Cur-rent expenditure for the eradication programme is in excess ofd800,000, considerably higher than original estimates.

4. Discussion

Whilst the eradication efforts in Holyhead Marina have not yetachieved the desired outcome, the lessons learned from theongoing D. vexillum management effort provide a valuable oppor-tunity to highlight some of the fundamental issues impeding theprogress of eradication programmes in the marine environment. Inaddition, a number of recommendations are presented, some newand some endorsing the views previously expressed by others,either specific to the UK or relevant to the cross-border challengesfacing the EU.

K. Sambrook et al. / Marine Policy 48 (2014) 51–58 53

The United Kingdom is composed of four nations, England,Scotland, Wales and Northern Ireland, each with devolved admin-istrations. The term Great Britain (GB) encompasses England,Scotland and Wales and is the level at which the D. vexilluminvasion was managed, rather than the whole of the UK. Howeverthe issues illustrated through discussions around the GB-levelmanagement actions on the incursion are applicable in a UKcontext in relation to the EU draft Regulation on IAS.

4.1. Alert systems linked to targeted monitoring effort

A topic not extensively discussed in the invasion literature, butrelevant to invasion management in Europe, is the merit of linkingalerts with targeted monitoring efforts. Early detection and rapidresponse are frequently acknowledged as core components ofsuccessful eradication [46,50–53], yet many non-native speciesare not detected until they reach a large population size [54,55].The report of D. vexillum in Wales triggered a GB-wide alert, issuedthrough the GB Non-Native Species Secretariat, a body establishedto assist with the co-ordination of management approaches toinvasive non-native species. Survey work carried out in late 2009in England and Scotland found additional D. vexillum populations,one year after the first observation in Wales. Three furtherestablished D. vexillum populations were found in southernEngland [56] and one on the west coast of Scotland [57]. Basedon the current example, the presence of D. vexillum on the eastcoast of Ireland, first reported in 2005 [42], should have triggeredan alert in Britain accompanied by action to monitor potential highrisk sites. Instead, the discovery of D. vexillum in Holyhead Marinawas made by a student as part of a research project and not as aresult of deliberate management efforts, despite the site experien-cing high maritime traffic from Ireland. In the absence of an alertsystem linked to mandatory targeted monitoring of high-risk sites,valuable time may have been lost in identifying additional popula-tions in Britain and reduced the range of potential managementoptions. To promote the chances of successful eradication, newincursions should be reported through a highly visible andrigorously tested EU-wide alert mechanism. In addition, MemberStates should implement time-constrained action plans to respondto high-risk IAS alerts, thus maximising the opportunity for earlydetection, the point at which eradication is deemed most likely tosucceed [37,50,53,58].

4.2. Science-based monitoring programmes for early detection

Significant emphasis has been placed on the importance ofmonitoring programmes for the early detection of non-nativespecies and the proposed EU Regulation on IAS states that MemberStates should have official surveillance systems in place within 18-months of the Regulation entering into force [16]. Althoughexamples of successful marine eradication programmes areincreasing [8,46], the majority of newly identified incursions arebeyond the point at which they can be controlled [13]. Someinvasive non-native species can proliferate rapidly giving man-agers a brief window of opportunity to consider eradication as afeasible option [59]. Therefore, designing monitoring programmesthat are capable of detecting small, newly establishing populationswill be fundamental for the successful delivery of eradicationprogrammes under the proposed EU Regulation on IAS.

Whilst eradication efforts continue in Wales, an annual mon-itoring campaign of high risk marinas has been established byNatural Resources Wales (previously CCW) with no further reportsof additional D. vexillum populations. Dedicated high frequencymonitoring campaigns are often only employed over the short-term to deal with a specific threat and in the current economicclimate, this level of intensive monitoring can be difficult to

resource over the longer-term. Input from the scientific commu-nity could help design efficient monitoring programmes groundedin science. Development of a generic management tool incorpor-ating life history traits, invader attributes, pathways and vectorscould allow environmental practitioners to design tailored mon-itoring programmes based on the selection of species from a listthat are considered high-risk within a specific locality. In addition,identifying the most appropriate methods for detecting marinenon-native species should be agreed on a case-by-case basis. InHolyhead Marina, as well as rapid assessment surveys, video-quadrats have been used to detect small colonies of D. vexillum andprovide a low cost, low resource supplementary support tool formonitoring D. vexillum [47].

4.3. Management action underpinned by science

A common criticism in the field of biological invasions is areported misalignment between scientific research and manage-ment needs [60–62]. However, early collaborative discussionsupon identification of a new invasive non-native species todetermine priority research gaps can improve the efficacy ofmanagement action on an invading species [21]. The finding ofD. vexillum by a Bangor University student led to a close workingrelationship between CCW and the university from the onset ofthe programme. Agreed priority tasks included laboratory andfieldwork to investigate the growth rates of D. vexillum colonies,the temporal nature and magnitude of recruitment and theenvironmental tolerances of D. vexillum compared to a closelyrelated native ascidian [49,63]. This work supplied evidence thatlarval recruitment in Holyhead Marina persisted until the watertemperature dropped below 9 1C [45,49], a consideration factoredinto the schedule for the second eradication attempt. Morerecently, work conducted in New Zealand to understand thedispersal of D. vexillum has shown a longer larval competencyperiod and therefore a much higher dispersal potential thanexpected [64]. Such knowledge is crucial to develop effective andrealistic management plans and highlights the importance ofunderstanding the fundamental biology and ecology of an invasivenon-native species.

As well as understanding the traits of non-native species,science-based research can provide practical insights into thesuitability of sites for potential invasions [65], identify impactson native species, monitor community-level change and assessrecovery rates post-eradication, particularly valuable where thetreatment method is indiscriminate. In order to conduct this typeof research, baseline data must be available on the site of interest,a requirement which forms an integral component of anotherMember State commitment, the Marine Strategy FrameworkDirective Descriptor 2 on non-indigenous species [66]. Baselinesurveys in Holyhead Marina were not conducted prior to the D.vexillum invasion but observations suggest that the biotic clear-ance of large areas within the marina has created space for thearrival of another non-native species, the encrusting bryozoanSchizoporella japonica (Ortmann, 1890), which is now abundant onmany surfaces [R. Holt pers obs]. Clearly quantification of recolo-nisation processes would be useful to address concerns relating tolong-term effects of indiscriminate eradication methods.

Taxonomists are often required to confirm the identity ofmarine non-native species but this expertise also has othervaluable applications [8,25,67]. Rapid assessment surveys havebeen broadly adopted across the UK and Ireland to search for non-natives in artificial marine environments such as marinas [35,68–71]. Using taxonomic experts, rapid assessment surveys can beconducted quickly and efficiently, although observations arerestricted to substrates accessible from the surface such as sidesof pontoons and ropes which can be pulled up and examined [68].

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Although recognised as a useful tool for monitoring non-nativespecies, rapid assessment surveys incur high costs due to the levelof expertise required and are labour intensive [68]. In the UK, thechronic shortage of suitably skilled taxonomic experts [72] limitsthe number of rapid assessment surveys that can be feasiblyundertaken. Working with environmental practitioners, taxo-nomic experts could play a critical role in training regionalagencies, conservation organisations, industry or citizen scientiststo increase opportunities for detection and indeed work on thishas begun in Great Britain [73]. A strong strategic steer toprioritise this action could accelerate the process and rapidlyexpand the UK's network of experts.

4.4. Rapid response through preparatory measures

The ability to act swiftly and decisively upon detection of anundesirable non-native species has been recognised as integral toeradication campaigns reporting successful outcomes [8,25,46,50,74].The draft EU Regulation on IAS outlines that eradication of IAS ofUnion concern should be attempted within three months of aMember State notifying the Commission of a new incursion [16].However, from initial detection to the start of the eradication pilottook 13 months for the D. vexillum invasion in Holyhead Marina.Examples of successful programmes where the speed of the responsewas within three months include the Californian Caulerpa taxifolia (C.Agardh, 1817) invasion which from detection to the start of eradica-tion took 17 days [75]; the parasitic sabellid polychaete incursion ona rocky shore in California where management action to remove hostgastropods began within a week [76] and in Australia, the Mytilopsissp. invasion in Darwin Harbour where the first eradication treat-ments commenced within a week and success was declared within amonth [59]. If the appropriate mechanisms had been in place to starteradication in the same year D. vexillum was first recorded in Wales,the process may have been more effective, resulting in fewer or lessintensive follow up treatments.

In the UK, management of marine incursions is still in itsrelative infancy with much uncertainty about navigating throughthe various agencies and lines of authority to achieve a rapidresponse. The GB Non-Native Species Secretariat formed a RapidResponse Working Group in 2008 to create a rapid responseprotocol which included a decision tree identifying relevant bodiesthat would need to be engaged with any rapid response activities.Although a useful preliminary mechanism which assisted CCW inelevating the risk profile of the D. vexillum incursion in Wales,issues remain with commitment and buy-in from appropriatestakeholders to achieve a time-constrained rapid response. InWales, the limited legislative and enforcement powers of CCWpresented the project team with several novel bureaucratic chal-lenges. A positive step was the designation of the incursion as a‘biological emergency’ expediting contractual and purchasingagreements. A similar status was awarded to the Caulerpa taxifoliainvasion in California which provided immediate access to acontingency fund usually reserved for oil spills and enablederadication work to begin within a month [75].

In Wales, inexperience in dealing with the complex multi-agency regulatory framework impeded progress resulting indelays and a failure to obtain the appropriate permits for triallingthe chemical treatment prior to the full-scale eradication attempt.Initiating dialogue with appropriate bodies at an early stage in thedevelopment of management plans may help to streamline pro-cesses in the future and increase the UK's capability to undertake arapid response. In Great Britain, Scotland has led the way instrengthening existing legislation to address the lack of ownershipin relation to non-native species issues. The Wildlife and NaturalEnvironment Act 2011 [77] gives public bodies greater powers toapply a ‘polluter pays’ principle when escapes, unintentional

transfers or spread of non-native species occurs, and introducesSpecies Control Orders which set out mandatory measures tocontrol or eradicate invasive non-native species. The amended Actdemonstrates Scotland's commitment to the management of non-native species and the adoption of similar measures by othercountries could significantly improve biosecurity.

At a GB-level, a standardised risk assessment framework has beendeveloped, which allows the risks presented by a non-native speciesto be evaluated based on available knowledge. Advisory in nature,risk assessments should be complemented with risk managementplans providing practical guidance for environmental managers inthe event of an incursion. Under the GB Non-Native SpeciesSecretariat, detailed risk management plans are anticipated to bedeveloped within the next 5–10 years, but with the pending EURegulation on IAS, these plans should receive higher priority toenable earlier delivery of an invaluable tool for practitioners.

4.5. Commitment of resources

Inadequate resources and insufficient funds have hindered pasteradication programmes [8,37,46] and both factors affected the D.vexillum management efforts in Wales. Financial constraints meantthat resources were limited for the size and complexity of theproject, resulting in a staggered treatment approach which wassubsequently cited as a contributing factor for the low success rateof the first eradication attempt. In addition, the short-termcommitment of financial support meant that funds to continuethe programme of work had to be sought from elsewhere resultingin a year's gap before the second eradication attempt, giving the D.vexillum population in Holyhead Marina time to recover andincreasing the window of opportunity for further inoculationevents. Eradication programmes in the marine environment maytake multiple attempts before success is achieved [40,78] owing tothe challenges of identifying small populations and the logistics ofworking underwater. Funding deficits leading to lengthy gapsbetween eradication treatments can negate the benefits of pre-ceding eradication work [51] and strategies to avoid a repetition ofthe scenario in Wales should be developed through for exampleidentification and ring fencing of a UK-wide contingency fund.

The practical experience gained by those involved in themanagement of the D. vexillum invasion in Holyhead Marina hasbeen valuable in building the capacity and knowledge within theUK to undertake a marine eradication programme. Whilst inex-perience does not necessarily lead to failure, building a strongnetwork of experts in the fields of taxonomy, ecology, biology,management and practical delivery will undoubtedly play a keyrole in future successes [25,26,53,75].

4.6. Cross-border challenges

The INNS Framework Strategy for Great Britain [79], coveringEngland, Scotland and Wales, states that where appropriate, rapidresponse aimed at eradicating new arrivals of invasive non-nativespecies should be the standard goal, a view shared by CCW and theWelsh Government which took decisive action to eradicate D.vexillum. Unfortunately the eradication programme has beendevalued for several reasons, specifically related to the cross-border nature of marine invasions. Although further populationswere identified in England and Scotland, neither of the nationalstatutory bodies responsible for nature conservation opted toeradicate D. vexillum for reasons including high eradication costs,lack of capacity, uncertainty surrounding the cost-benefit of actionand re-inoculation risks from other sources [56,80]. In addition,populations of D. vexillum are present in Ireland and have beenfound more recently in Northern Ireland [81]. Therefore even if theeradication programme at Holyhead Marina is ultimately

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successful, D. vexillum will still be present in other neighbouringregions and could easily be reintroduced into Wales.

The risk of re-inoculation in Wales is exacerbated by a lack ofmeasures to manage the pathways of spread. A GB DidemnumWorking Group was established in July 2009 to provide guidanceon the D. vexillum situation in Great Britain. When it appeared thatthe eradication of all GB-populations of D. vexillum would not beattempted, the group prioritised an action to investigate how therate of spread and reinvasion risks could be reduced [82]. Fivepotential pathways were evaluated: recreational boating, fisheriesand aquaculture, ship recycling, marine industries and commercialshipping, with priority recommendations including improvedmanagement of biofouling, education and awareness raising,voluntary vector controls and the need to look to nations withmore highly developed biosecurity systems for examples of goodpractice [82]. In terms of recreational boating, considered to be theoriginal inoculation source for D. vexillum in Holyhead Marina, theworking group recommended the development of a cost-effectiveand rapid system for disinfecting vessels entering or exiting D.vexillum areas, which could also be applied to other marineincursion scenarios. Wales has led on this initiative and work inHolyhead Marina involving the marina operators and academicsfrom Bangor University is ongoing to trial an in-water decontami-nation berth for the rapid removal and containment of biofoulingmaterial from vessel hulls. Although still in the preliminary testingphase, it is hoped that if successful, this solution could be deployednationwide to complement rather than replace longer-term anti-fouling treatment methods. The ability to subsidise the installationto keep costs to a minimum for vessel owners and marinaoperators will likely be a key factor in the achievement of this goal.

As part of Australia's biosecurity system, marina operators areobligated to record vessels entering and exiting the marina [59].During the Mytilopsis sp. incursion in Darwin Harbour, this systemenabled vessels which had visited the infected marinas within thepast six months to be tracked and located. Working with boatyardoperators and the fishing industry, vessels were inspected for furtherpopulations of Mytilopsis sp. and treated where necessary [59]. Thecapacity to implement these measures is valuable in reducing therisk of secondary spread and enhancing the effectiveness of eradica-tion programmes. Introducing comparable measures in the UK andthroughout the EU, complemented by decontamination berths, couldsignificantly increase the value of localised eradication campaigns.

The creation of the GB Non-Native Species Secretariat wasdesigned in recognition of the cross-border issues associated withthe management of non-native species in a region where severalnations share geographical borders. The development of guidancesuch as the rapid response protocol and standardised risk assess-ment framework assists nations on the British mainland to workcollaboratively towards shared goals in a cohesive manner. Furtherdevelopment of this mechanism combined with transnationalprojects to focus on priority areas should help to build a moreco-ordinated approach to management and improve efficacy ofmanagement actions in the future.

4.7. The European Union and the proposed Regulation on IAS

The EU does not have a strong success record in eradicatingnon-native species, and managing marine invasions appears to bea particular area of weakness [51]. If the proposed EU Regulationenters into force incorporating the objective to undertake rapideradication of IAS of Union concern, Member States will need toimplement a number of steps to increase the probability of asuccessful outcome. Priority actions for Member States include thedevelopment of effective monitoring programmes, robust andtested frameworks to facilitate a rapid response, the ability to

access funds to support rapid action and capacity building in termsof expertise and pooled resources.

However, the European Union has an important role to play asa knowledge gathering and coordinating body assisting MemberStates to achieve the goal of rapid eradication by the provision ofstandardised risk assessment frameworks and proven incursionresponse tools. The EU should look to nations with advancedbiosecurity frameworks such as Australia and New Zealand forexamples of good practice [13,19,21,26,83,84]. The cross-bordernature of invasions in Europe will mean that tools and guidancewill need to be tailored to meet the European Union's morecomplex infrastructure. Providing a centralised source of suchinformation will help Member States to respond rapidly and it ishoped that this will be addressed under the remit of the newEuropean Alien Species Information Network (EASIN) [83].

In addition, there is a strong likelihood that nations may havedifferent priorities or concerns when a non-native species not listedas an IAS of Union concern is detected. It will therefore be importantthat investment in eradication programmes is not solely reserved forIAS of Union concern. Whilst not discussed in-depth here, riskassessments and risk management plans are integral componentsof the decision-making process on the management of non-nativespecies. As part of the EU-level work to address IAS of Union concern,a standardised management framework should be developed thatMember States can use to make internal decisions about when toinstigate a rapid response to a novel incursion.

5. Conclusions

The United Kingdom is often cited within the European Unionas having made significant progress in the field of invasionmanagement [85]. However, the D. vexillum incursion in HolyheadMarina, North Wales illustrates that the UK is currently inade-quately prepared to enforce the proposed EU Regulation on IAS inrelation to rapid eradication action in the marine environment.There is a risk that unless steps are taken now to streamlineprocesses and build capacity to apply rapid response measures, theUK will not be able to meet future EU obligations. Whilst the keyprinciples of factors contributing towards a successful eradicationprogramme are well understood, direct application of these factorsto eradication scenarios remains poor [86]. With the Regulationunlikely to enter into force for several years, the UK now has theopportunity and motivation to develop a biosecurity frameworkgrounded in science that will enable more effective managementof invasive non-native species in the marine environment. Eradi-cation, although difficult, is feasible in the marine environmentwhen detected early and should be encouraged where there is arisk of damage to economy, environment and or social well-being.

Acknowledgements

We would like to thank Anglesey Divers and Dive North Waleswho were the principal dive teams for the in-water elements ofthe eradication. In addition, we acknowledge the hard work ofstaff from CCW (now NRW) and Holyhead Marina, as well asvolunteers who dedicated significant amounts of time throughseveral winters to assist the eradication efforts.

The views expressed herein are those of the authors and do notnecessarily reflect those of Natural Resources Wales.

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