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Wireweed © Lorne Gill/SNH Authors Fiona Manson Scottish Natural Heritage, Battleby, Redgorton, Perth, PH1 3EW. [email protected] David Donnan Scottish Natural Heritage, Battleby, Redgorton, Perth, PH1 3EW. [email protected] Iain Macdonald Scottish Natural Heritage, Great Glen House, Leachkin Road, Inverness, IV3 8NW. [email protected] Summary • Wireweed (Sargassum muticum) is large brown alga from the Western Pacific that has been introduced to Europe, where it is an invasive, non-native species posing a significant risk to marine biodiversity, primarily through competition with indigenous marine algae and seagrass species. • In Scotland it was first recorded from Loch Ryan in 2004, since when it has spread rapidly along the west coast, reaching South Uist by 2013. • To identify coastal areas where the establishment of wireweed was most likely, as part of the Species Action Framework (SAF) project, an ‘occurrence-pathway’ modelling approach was developed, incorporating factors such as wind and tide direction, wave and current information. Surveys were carried out at locations predicted to be vulnerable to colonisation. Introduction Species background Wireweed (Sargassum muticum) is an olive-brown alga growing to more than a metre long (Fig. 1). It is native to the western Pacific, but has been introduced to other parts of the world including the eastern Pacific and eastern Atlantic. It was first recorded in the UK in 1973 at the Isle of Wight and has since spread along the south coast of England, to Wales and around Ireland. The first reports of wireweed in Scotland were in Loch Ryan in 2004, since when it has spread rapidly along the west coast. By early 2007 populations had been found at Great Cumbrae Island, the north Ayrshire coast, Arran and at Claonaig on the Mull of Kintyre (Davison, 2009). • A public relations campaign was carried out to raise awareness of wireweed and to encourage the reporting of new records to complement the targeted surveys. • A detailed review of the ecology of wireweed was commissioned in support of the SAF project. • The SAF surveys indicate that wireweed has spread along a significant part of the western Scottish coast. The Scottish and wider global distribution of wireweed is such that eradication from Scotland is not now possible, and further expansion cannot be prevented. • Except where it is locally a nuisance, control of wireweed is unlikely to be effective and the species will become part of the Scottish coastal ecosystem. • Three wider conclusions are drawn: 1. Non-native species management should be targeted at preventing the introduction of marine non-native species, as once they are established they are very difficult to remove. 2.Involvement of the public is important in identifying the spread of a species, and in preventing introductions. 3.Management of marine non-natives needs to be done in collaboration with neighbouring countries. Fig 1. Wireweed. © Lorne Gill/ SNH Why was this species on the Species Action Framework list? In Europe, wireweed is an invasive, non-native species which meets criterion 2 of the Species Action Framework (SAF), as posing a significant risk to Scottish marine biodiversity, primarily through competition with indigenous marine algae and seagrass species (Scottish Natural Heritage, 2007). The ongoing dispersal of wireweed along Scotland’s coastline has implications for the suite of nationally and internationally important marine protected areas established around the Scottish coast and for waterbodies meeting environmental objectives of good ecological status under the Water Framework Directive. The arrival of wireweed in Scotland in 2004 provided an opportunity for scientists and conservation managers to study the way that an invasive non-native species has established and spread in Scottish waters, as well as how invasive species can best be managed. Although it was not possible to prevent the further spread of wireweed, lessons could be learned from its arrival to help develop strategies for preventing and controlling future introductions of invasive species. SAF could also be instrumental in raising awareness of the problems associated with non-native species, the importance of preventing their arrival and the difficulties of controlling them once they are here. Habitat, distribution and abundance was known to occur at a few sites in south-west Scotland in Loch Ryan and the Firth of Clyde. The west coast of Scotland was regarded as providing a large extent of potentially suitable habitat for the establishment of wireweed, and since 2007 it has been recorded at several sites as far north as Skye and North Uist. General ecology Wireweed plants have long fronds with side branches that hang like washing from a line (Fig. 3). In autumn the branches break off from the basal structure and, owing to their distinctive grape-like air bladders, can be found floating individually or in a large mass. These detached fronds remain reproductively capable and contribute to the species’ ability to spread rapidly. The base of the plant remains attached to the rock and will regenerate new branches in the spring time. Wireweed usually grows attached to rocky substrates close to the lower shore or in shallow, sub-tidal waters or in mid-shore rock pools (Fig. 2). It is also found on sandy or muddy shores if stones are present to which the plants can attach. Wireweed prefers sheltered habitats as it can be damaged by wave action in more exposed sites. Fig 2. Wireweed in rock pool, Great Cumbrae Island, Firth of Clyde. © Lorne Gill/SNH The natural range of wireweed is thought to be the western Pacific region. It is likely to have been introduced to the eastern Atlantic in the late 1960s or early 1970s. Since then, it has colonised parts of the Atlantic coast from Morocco to Norway and as far west as the Republic of Ireland. In Scotland, at the start of the SAF project, wireweed Fig 3. Wireweed has a distinctive appearance with numerous side branches hanging from the main frond. © SNH Wireweed can tolerate wide ranges of temperature and salinity. The competitive ability of wireweed may be reduced at lower salinities, for example at the head of sea lochs with a high freshwater input (Steen, 2004). A detailed review of the ecology of wireweed, commissioned in support of the SAF project, can be found in Davison (2009). History of invasion and current threats Marine non-native species can be transported around the world either intentionally, for example as live seafood or for aquaria, or accidentally, for example on the hulls of boats or in ballast water (Hewitt et al., 2007). In the case of wireweed, the method of transportation is not known, but it may have been introduced around the world as germlings transported alongside Pacific oysters destined for shellfish farming (Cheang et al., 2010). Transport over short distances may occur if wireweed fronds become entangled in boating equipment, such as anchors, and are then released in a new area. Most marine non-native species in Scottish waters are unlikely to have arrived directly from their native origin (Donnan and Manson, 2010). It is likely that wireweed arrived in Scotland from introduced populations in adjacent waters. It is a fast-growing species able to form dense stands where conditions suit and is ideally adapted to spread rapidly once established in a new region. Detached fronds can remain reproductively active for several weeks enabling dispersal over a wide area. Wireweed can quickly exploit open spaces that become available and it is considered to be an ‘opportunistic gap-grabber’. The spread of wireweed, through competion with native algae, can lead to changes in the local habitat and consequently the local fauna (Salvaterra et al., 2013). It has the potential to replace native species, possibly out-competing them for light and substrate (Harries et al., 2007a). The replacement of native species by a non-native species can have a direct impact on the biodiversity of an area by causing a shift in marine communities and their trophic food webs. Seagrass beds on soft sediments can be colonised by wireweed, with the seagrass appearing to act as a hard substrate for attachment (Tweedley et al., 2008). Attachment to clams living within seagrass beds has also been noted. Once such beds have been colonised there is potential for the wireweed to outcompete the seagrass, therefore greatly altering the habitat as a whole (White and Orr, 2011). As seagrass beds are of high conservation importance, invasion by wireweed is of concern. In addition to having an ecological impact, wireweed is considered a nuisance in harbours and shallow waters where large floating masses may become a hazard to commercial and recreational boating through entangling in propellers or blocking engine cooling systems. The floating mats can also affect water sports such as swimming, wind surfing and sailing. Wireweed can foul fishing nets and lines and can seriously impact on oyster beds and other aquaculture structures. Aims Aims for 2007-2012 • To assess the spread of wireweed and identify its impacts on biodiversity. • To develop and implement a control strategy to prevent the further spread of wireweed and reduce its impact on native biodiversity. Action under SAF At the start of the SAF project the spread of wireweed along the west coast of Scotland as far as the Outer Hebrides was predicted within the ‘next few years’ (Harries et al., 2007b). A review of information, issues and implications was carried out for wireweed to support the SAF project (Davison, 2009). The main focus of the project was then to determine the distribution and spread of wireweed, and to raise awareness. Mapping the distribution of wireweed In order to track the spread of wireweed in Scotland, two complementary approaches were used: • Surveys were carried out at locations predicted to be vulnerable to colonisation. • A public relations campaign was carried out to raise awareness of wireweed and to encourage the reporting of new records. To identify coastal areas where the establishment of wireweed was most likely, an ‘occurrence-pathway’ modelling approach was developed, incorporating factors such as wind and tide direction, wave and current information (Trendall et al., 2010). The model predicted high risk areas (Fig. 4). Dedicated surveys between the Solway Firth and the Ardnamurchan peninsula were also commissioned by SNH to establish the extent of wireweed at both the reported sites and predicted sites (Trendall et al., 2010) (Fig. 5). During 2008, the surveys found wireweed to be widely distributed throughout the Firth of Clyde, forming dense stands at some locations. In particular, stands of wireweed were found around the islands of Cumbrae and Arran and along the Ayrshire coast near Largs, Ardrossan, Culzean and Maidens. Outwith the Firth of Clyde, attached plants were found only at West Loch Tarbert. However by autumn 2008, established populations were also reported in Loch Sunart and the Isle of Skye. Fig 4. High risk areas for colonisation by wireweed 2009. © SNH Fig 5. Surveying for wireweed in Argyll. © SNH Comparing the model with the results of the dedicated survey, the model proved to be a successful tool in predicting the spread of wireweed (Trendall et al., 2010). Many of the predicted sites for wireweed were either confirmed during the field survey or from subsequent reports. Of particular conservation concern is that wireweed was found attached at two Special Areas of Conservation (Luce Bay and Sands, and Sunart). Floating fragments were also found in the Firth of Lorn Special Area of Conservation. To help record the spread of wireweed over a greater extent than it was possible to survey, a public sightings campaign was launched by SNH. A webpage and telephone reporting service were established. The public campaign resulted in reports of wireweed from as far south as Luce Bay in the Solway Firth to as far north as Loch Sunart in Ardnamurchan and Tarskavaig on Skye by 2008. Wireweed was found to be widespread throughout the Firth of Clyde. Conducting a dedicated survey over such a large area would have been impractical. The public campaign demonstrated that involving the public is an effective means of extending the scope of dedicated survey. The combined results of SNH surveys and the public sightings campaign by the end of 2008 are presented in Fig. 6. These results show that wireweed has spread significantly since its first recorded sighting in Scotland in 2004 and is now well established along the coast of western Scotland. A more recent report from 2013 shows that wireweed has reached North Uist in the Western Isles. Fig 6. Distribution of wireweed, 2008. © Crown copyright and database right 2009. All rights reserved. Ordnance Survey Licence number 100017908. The results of the survey and public campaign have been presented as a case study in the SNH publication Species Management: Challenges and Solutions for the 21st Century (Donnan and Manson, 2010). Publications associated with the SAF project The following publications are either direct outputs from, or have been informed by, the SAF wireweed project: • Harries et al. (2007b) – reviews the dispersal and establishment of wireweed and identifies potential new areas in Scotland for colonisation. • Davison (2009) – provides a review of the main issues associated with wireweed. • Trendall et al. (2010) – models the spread of wireweed in Scotland and reports on surveys to assess its distribution. • Donnan and Manson (2010) – gives an overview of invasive marine species in Scotland, with specific reference to wireweed. Lessons Learnt, Further Work and Future Recommendations Options for the control of wireweed in Scotland It is evident that wireweed is well established along the European coast. The results of the SAF survey indicate that wireweed has also spread along a significant part of the western Scottish coast. Even if wireweed could be controlled locally in Scotland, any large scale control would require international co-operation. It is likely that the Scottish and international distribution of wireweed is such that eradication from Scotland is not now possible. It is also likely that further expansion of wireweed in Scotland cannot be prevented. Except where it is locally a nuisance, control of wireweed in Scotland is unlikely to be effective and the species is likely to become part of the Scottish coastal ecosystem. Lessons learnt The wider conclusions from the project are: • Non-native species management should be targeted at preventing the introduction of marine non-native species, as once they are established they are very difficult to remove. • Involvement of the public is important in identifying the spread of a species, and in preventing introductions. • Management of marine non-natives needs to be done in collaboration with neighbouring countries. Future recommendations Including wireweed within the SAF project has helped to raise the profile of marine non-native species. Over a thousand marine non-native species have been identified in European waters (Katsanevakis et al., 2013). Ninety non-native species have been identified in British brackish and marine waters, of which 58 are established (Minchin et al., 2013). Although many marine non-native species are unlikely to have a negative impact, some can cause local shifts in the assemblages of native species (Kelly et al., 2011). Wireweed is one such species. Other, as yet unidentified species could have a highly negative impact upon Scottish coastal ecosystems and the coastal economy. With regard to wireweed it is recommended that the distribution should continue to be recorded, particularly during the current colonisation of new parts of the Scottish coast. Particular attention should be directed towards Special Areas of Conservation and lagoon systems where wireweed has the potential to have a negative impact upon native biodiversity (Trendall et al., 2010). Relative to other marine non-native species, wireweed has been extensively researched. Research should continue into the longer term impacts on Scottish coastal ecology. The case study of wireweed has relevance to other marine non-native species including influencing future policy and advice. Priorities for the future should be to predict, record and, where possible, eradicate new invasive species; as well as to control the further spread of existing marine non-native species. Since the start of the SAF project, Scotland has made significant progress towards meeting these priorities, notably through the work of the Firth of Clyde Forum. Key Management Messages • Eradication of wireweed from the Scottish coast is not likely. • Local control of wireweed is an option where wireweed presents a nuisance. • It is likely that wireweed will continue to spread into suitable habitats around the Scottish coast. • Early detection of new marine non-native species is a high priority, requiring international cooperation. New and on-going work since SAF ended The following developments have taken place: • http://www.ogp.org.uk/pubs/436.pdf – alien invasive species and oil and gas industry – guidance for prevention and management. – OGP/ IPIECA 2010. • SNH has continued to collate records of wireweed. Sightings can be submitted via the SNH website. Wireweed has been reported from the strandline of a beach in North Uist in August 2013, extending its known Scottish distribution to the north and west. • http://www.snh.gov.uk/protecting-scotlandsnature/nonnative-species/ – SNH web pages on non-native species issues. • The Firth of Clyde Forum produced a Biosecurity Plan for the Firth of Clyde 2012–2016. References • The Firth of Clyde Forum and Scottish Natural Heritage have produced a series of documents on marine biosecurity planning, including: a review of best practice (Cook et al., 2014); guidance for producing site and operationbased plans for preventing the introduction of non-native species (Payne et al., 2014a); and a dissemination strategy and communications plan (Payne et al., 2014b). Cheang CC, Chu KH, Fujita D, Yoshida G, Hiraoka M, Critchley A, Choi HG, Duan DL, Serisawa Y, Ang PO. 2010. Low genetic variability of Sargassum muticum (Phaeophyceae) revealed by a global analysis of native and introduced populations. Journal of Phycology 46: 1063-1074. • In 2013 SNH, Scottish Government and the Scottish Association for Marine Science (SAMS) trialled an early warning system for non-native species around and off the Scottish coast (Cook et al., 2015). Further Information • http://www.snh.gov.uk/land-and-sea/ managing-coasts-and-sea/marine-nonnatives/ wireweed/ – summary information on wireweed, including a link on how to report new sightings. • http://www.scotland.gov.uk/ Publications/2012/08/7367 – Non-Native Species Code of Practice. Scottish Government 2012. • http://www.biodiversityscotland.gov.uk/ doing/tackling/nonnative/ – summary information on tackling non-native species in Scotland, including useful further links. Scottish Biodiversity Forum. • http://clydeforum.com/index.php/projects/ invasive-species – the Clyde Forum Guidance on non-native species. • http://www.nonnativespecies.org/index. cfm?pageid=174 – GB non-native species secretariat guidance on biosecurity in the field. Cook EJ, Beveridge C, Twigg G, Macleod A. 2015. Assessing the effectiveness of early warning systems for the detection of marine invasive non-native species in Scottish waters. Scottish Natural Heritage Commissioned Report 874, Battleby, Perth. Cook EJ, Payne R, Macleod A. 2014. Marine Biosecurity Planning – Identification of best practice: A Review. Scottish Natural Heritage Commissioned Report 748, Battleby, Perth. Davison DM. 2009. Sargassum muticum in Scotland, 2008: A review of information, issues and implications. Scottish Natural Heritage Commissioned Report 324, Battleby, Perth. Donnan DW, Manson FJ. 2010. Invasive non-native species in Scotland’s seas: risk and reality. In Species Management: Challenges and Solutions for the 21st Century, Baxter JM, Galbraith CA (eds). TSO Scotland: Edinburgh; 265-283. Harries DB, Harrow S, Wilson JR, Mair JM, Donnan DW. 2007a. The establishment of the invasive alga Sargasssum muticum on the west coast of Scotland: a preliminary assessment of community effects. Journal of the Marine Biological Association of the United Kingdom 87: 1057-1067. Harries DB, Cook E, Donnan DW, Mair JM, Harrow S, Wilson JR. 2007b. The establishment of the invasive alga Sargassum muticum on the west coast of Scotland: Rapid northwards spread and identification of potential new areas for colonisation. Aquatic Invasions 2: 367-377. Hewitt CL, Campbell ML, Schaffelke B. 2007. Introductions of seaweeds: accidental transfer pathways and mechanisms. Botanica Marina 50: 326-337. Acknowledgements Katsanevakis S, Zenetos A, Belchior C, Cardoso AC. 2013. Invading European Seas: Assessing pathways of introduction of marine aliens. Ocean & Coastal Management 76: 64-74. We would like to thank all the members of the public who responded to the request for wireweed sightings. Without their help we would not have been able to chart the distribution of wireweed as effectively. Kelly JR, Scheibling RE, Balch T. 2011. Invasionmediated shifts in the macrobenthic assemblage of a rocky subtidal ecosystem. Marine Ecology Progress Series 437: 69-78. Several partner organisations listed below helped with the surveys and provided expert opinion on wireweed. Minchin D, Cook EJ, Clark PF. 2013. Alien species in British brackish and marine waters. Aquatic Invasions 8: 3-19. Payne R, Cook EJ, Macleod A. 2014a. Marine Biosecurity Planning – Guidance for producing site and operation-based plans for preventing the introduction of non-native species. Report to the Firth of Clyde Forum and Scottish Natural Heritage. Ref. 00954. SRSL Ltd, Scottish Marine Institute, Oban. The SAF Partners Payne R, Cook EJ, Macleod A. 2014b. Marine Biosecurity Planning – Dissemination Strategy and Communications Plan. Report to the Firth of Clyde Forum and Scottish Natural Heritage. SRSL Ltd, Scottish Marine Institute, Oban. • Scottish Association of Marine Science Salvaterra T, Green DS, Crowe TP, O’Gorman EJ. 2013. Impacts of the invasive alga Sargassum muticum on ecosystem functioning and food web structure. Biological Invasions 15: 2563-2576. Steen H. 2004. Effects of reduced salinity on reproduction and germling development in Sargassum muticum (Phaeophyceae, Fucales). European Journal of Phycology 39: 293-299. Trendall JR, Bedford G, Lawton P, Davison DM, Fortune F, Saunders G. 2010. Assessment of the spread of the non-native species Sargassum muticum: Solway Firth to the Ardnamurchan Peninsula. Scottish Natural Heritage Commissioned Report 347, Battleby, Perth. Tweedley JR, Jackson EL, Attrill MJ. 2008. Zostera marina seagrass beds enhance the attachment of the invasive alga Sargassum muticum in soft sediments. Marine Ecology Progress Series 354: 305-309. White LF, Orr LC. 2011. Native clams facilitate invasive species in an eelgrass bed. Marine Ecology Progress Series 424: 87-95. • Heriot-Watt University • Joint Nature Conservation Committee • Marine Scotland Science • Scottish Natural Heritage • Scottish Environment Protection Agency • University Marine Biological Station Millport The Species Action Framework Handbook This account comes from the Species Action Framework Handbook published by Scottish Natural Heritage. For more information on the handbook please go to www.snh.gov.uk/ speciesactionframework. This document should be cited as follows: : Manson F, Donnan D, Macdonald I. 2016. Wireweed. Version 1.0. In The Species Action Framework Handbook, Gaywood MJ, Boon PJ, Thompson DBA, Strachan IM (eds). Scottish Natural Heritage, Battleby, Perth.