Download Wireweed - Scottish Natural Heritage

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.