Scottish Natural Heritage Commissioned Report No. 324 Sargassum muticum in Scotland 2008: a review of information, issues and implications COMMISSIONED REPORT Commissioned Report No. 324 Sargassum muticum in Scotland, 2008: A review of information, issues and implications For further information on this report please contact: Fiona Manson Scottish Natural Heritage Battleby, Redgorton Perth, PH1 3EW Telephone: 01738 444177 E-mail: [email protected] This report should be quoted as: Davison, D.M. (2009). Sargassum muticum in Scotland 2008: a review of information, issues and implications. Scottish Natural Heritage Commissioned Report No.324 (ROAME No. R07AC707) This report, or any part of it, should not be reproduced without the permission of Scottish Natural Heritage. This permission will not be withheld unreasonably. The views expressed by the author(s) of this report should not be taken as the views and policies of Scottish Natural Heritage. © Scottish Natural Heritage 2007. COMMISSIONED REPORT Summary Sargassum muticum in Scotland 2008: A review of information, issues and implications Commissioned Report No. 324 Contractor: Dee Davison Associates, for Royal Haskoning Year of publication: 2009 Sargassum muticum is an invasive, non-native species of brown algae. S. muticum was first recorded in the UK in 1973 on the Isle of Wight and has since spread along the south coast of England, around Wales and around Ireland. The first reports of S. muticum in Scotland were in Loch Ryan in 2004 and by April 2007, populations had also been found at Great Cumbrae Island, the North Ayrshire coast, Arran and at Campbeltown Loch on the Mull of Kintyre. Drifting fragments of S. muticum had been recorded from Loch Fyne, Argyll and the Clyde Marina, Ardrossan, Ayrshire as well as on Arran and at Clonaig on the Mull of Kintyre. It had been thought that the Kintyre Peninsula would provide a temporary physical barrier to the continued spread of this invasive species up the west coast of Scotland. However, during early 2007, unattached drift S. muticum fragments were found in the Firth of Lorn at the Garvellachs and at Ganavan, near Oban. S. muticum is a fast growing species and once established, colonies can form dense stands. In summer, the floating fronds spread out over the surface, creating a distinctive canopy. S. muticum quickly exploits any open spaces that become available and it is considered to be an ‘opportunistic gap-grabber or space-filler’. Concerns have been expressed about the potential for deleterious ecological change, where S. muticum displaces native species of algae or Zostera sp., or alters habitat characteristics. The introduction of S. muticum can have a number of other implications that relate to the amenity, recreational and commercial uses of coastal areas. S. muticum has been identified for inclusion in Scottish Natural Heritage’s Species Action Framework as an active invasive with high potential for adverse impact on important biodiversity features. The ongoing dispersal of S. muticum along Scotland’s coastline has implications for the suite of nationally and internationally important marine protected areas established around the Scottish coast and for water bodies meeting environmental objectives of good ecological status under the Water Framework Directive. A literature review of national and international research on S. muticum was undertaken. This report collates this information in a structured form that aims to provide context for the prediction of the potential spread of S. muticum in Scotland and to inform assessments of impacts and any future management plans and actions. The report provides background information on this species, its habitat preferences and environmental tolerances and the features and strategies that it employs to facilitate its dispersal. The anthropogenic vectors responsible for the global spread of S. muticum are described and an overview of its current global distribution is provided. The report presents an overview of the ecological, economic and natural heritage implications of S. muticum introductions, as well as management strategies and eradication techniques that have been employed, including a case study of Strangford Lough. For further information on this project contact: Fiona Manson, Scottish Natural Heritage, Battleby, Redgorton, Perth, PH1 3EW Tel: 01738 458641 Email: [email protected] For further information on the SNH Research & Technical Support Programme contact: Policy & Advice Directorate Support, SNH, Great Glen House, Leachkin Road, Inverness, IV3 8NW. Tel: 01463 72500 or [email protected] CONTENTS Section Page 1.0 Introduction 1 2.0 Sargassum muticum: a description 2 3.0 Habitat preferences and environmental tolerances of Sargassum muticum 8 3.1 Zonation 8 3.2 Exposure tolerance 8 3.3 Substrate preferences 9 3.4 Growth conditions 10 3.5 Competitive ability with native algae 13 3.6 Susceptibility to herbivorous grazing 16 3.7 Overview of habitats where Sargassum muticum is currently found 18 4.0 Adaptations of Sargassum muticum that facilitate its dispersal and the global 23 extension of its range 4.1 Growth features 23 4.2 Regeneration features 30 4.3 Reproductive features and strategies 30 4.4 Settlement features and strategies 41 4.5 Dispersal and colonisation strategies 43 4.6 Overview of the features and strategies that makes S. muticum such a successful 47 invasive coloniser 5.0 Vectors in the spread of Sargassum muticum 49 5.1 Oyster cultivation 50 5.2 Commercial and recreational vessels 52 6.0 Overview of the current global distribution of Sargassum muticum 53 6.1 Dispersal rates of Sargassum muticum 53 6.2 The distribution of Sargassum muticum in the western Pacific 54 6.3 The distribution of Sargassum muticum along the eastern Pacific coast of North 54 America 6.4 The distribution of Sargassum muticum along the European coastline 55 6.5 The known distribution of Sargassum muticum around the British Isles 66 7.0 The ecological, economic and natural heritage implications of the introduction 77 of Sargassum muticum 7.1 The impacts of Sargassum muticum on the physical under-canopy environment 79 7.2 Sargassum muticum beds as a habitat 80 7.3 Competition with eel grass, Zostera marina 83 7.4 Competition with indigenous algae 85 7.5 Epibionts on Sargassum muticum 90 7.6 Economic impacts 97 7.7 Natural heritage implications 98 8.0 Management strategies and eradication techniques 100 8.1 General management issues and strategies regarding the introduction of species 100 8.2 U.K. management issues and concerns 102 8.3 U.K. methods of monitoring Sargassum muticum populations 102 8.4 Review of the development of management strategies on the south coast of England 103 CONTENTS continued 8.5 Review of the implementation of an eradication programme on the south coast of 104 England 8.6 The Strangford Lough containment operation 108 9.0 Case study: Sargassum muticum in Strangford Lough 111 9.1 Introduction and colonisation: 1987 - 1998 112 9.2 The distribution of Sargassum muticum within Strangford Lough: 1995 – 2003 118 9.3 Modelling the spread of Sargassum muticum in Strangford Lough 131 9.4 Research work undertaken on Sargassum muticum in Strangford Lough: 2000 – 132 2003 10.0 The current known distribution of Sargassum muticum around Scotland 138 10.1 The discovery and subsequent records of current known populations in Scotland 138 10.2 The potential introduction vectors 147 11.0 The projected expansion of the Scottish distribution of Sargassum muticum 149 11.1 Dispersal mechanisms and vectors for Sargassum muticum along the Scottish 150 coastline 11.2 Habitat preferences and environmental tolerances of Sargassum muticum in 151 Scotland 11.3 Predicting the future dispersal of Sargassum muticum around Scotland’s coastline 156 11.4 Potential ecological, economic and natural heritage consequences 159 11.5 Management strategies for Sargassum muticum in Scottish coastal waters 161 12.0 References 165 13.0 Glossary of terms 185 FIGURES Figure Title Page Figure 1 Indigenous algae that may be confused with Sargassum muticum 3 Figure 2 The plant structure of Sargassum muticum 5 Figure 3 Illustration of Sargassum muticum plant 6 Figure 4 The morphology of Sargassum muticum 7 Figure 5 Annual variation in the mean thallus biomass (dry weight) and mean primary lateral 26 length for Sargassum muticum collected from the Dorn, Strangford Lough: 2000- 2002 Figure 6 An age-specific morphological of Sargassum muticum 29 Figure 7 The life cycle of Sargassum muticum 31 Figure 8 S. muticum from Strangford Lough, 1995, Sexual development stage I: vegetative 34 tissue only Figure 9 S. muticum from Strangford Lough, 1995, Sexual development stage IIIa: Well 35 developed receptacles and maturing conceptacles, no zygotes Figure 10 S. muticum from Strangford Lough, 1995, Sexual development stage IV: Mature 36 receptacles and conceptacles, zygotes obvious on the surface Figure 11 S. muticum from Strangford Lough, 1995, Sexual development stage IV: Mature 37 receptacles and conceptacles, zygotes obvious on the surface Figure 12 S. muticum from Strangford Lough, 1995, Sexual development stage IV: Zygotes 38 obvious on the surface Figure 13 Reproductive periods of Sargassum muticum at different latitudes 40 Figure 14 The dispersal mechanisms of Sargassum muticum and their potential range 43 Figure 15 Map illustrating the chronology of European records, drift and attached, for S. 62 muticum: 1973-1976 Figure 16 Map illustrating the chronology of European records, drift and attached, for