SHELLFISHING WITH SARGASSUM: An assessment of the current distribution and potential control options for the introduced brown alga Sargassum muticum in Scotland

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Executive Summary
Sargassum muticum (commonly known as Japweed) is an invasive, large brown seaweed, with fronds usually over 1 m in length. This species originates in Asia and, in addition to environmental concerns (i.e. out-competing local species), it may cause serious economic losses in the shellfish industry by smothering bivalves and reducing feeding rates. S. muticum has recently been identified in Loch Fyne (June 2006) and the Firth of Lorn (July 2007), west coast of Scotland which are highly productive regions for scallop fisheries and shellfish culture. Eradication methods are typically considered unpractical unless the spread is caught early and all previous attempts at controlling or eradicating established populations of S. muticum have proved unsuccessful and have sometimes been counter-productive. The spread of S. muticum in Scotland, particularly Loch Fyne and the Firth of Lorn is fortunately still in its early stages and this provides an ideal opportunity to attempt to control the northwards spread of this species. In addition, new techniques for the control of invasive macroalgae have been developed in recent years and their advantages and disadvantages are discussed.
This study has shown that currently, the only practical option for controlling the establishment of S. muticum on discovery of this species is the physical removal of unattached or attached plants, either by shore based workers or by SCUBA divers. However, this method requires regular monitoring and repeated removal efforts, especially if the source of the introduction is unknown or can not be controlled. The main problem is the difficulty of locating all individual plants including small individuals and the inconspicuous holdfasts. The plants can rapidly regenerate from overlooked holdfasts and disturbance caused by the removal efforts can create ideal conditions for settlement and rapid growth. An additional concern is that plant fragments accidentally left on the shore following removal efforts could accelerate dispersal of the species by drifting to neighbouring areas. Heat treatment of shellfish prior to translocation is also considered a priority for controlling the spread of S. muticum between sites.
Recent advances in the development of species-specific biocides for invasive macroalgae that target physiological processes offer significant advantages over traditional non-selective herbicides and management options which combine treatments, such as biological and chemical control agents could provide a long term solution to eradicating invasive macroalgae, such as S. muticum. Further investigation into eradication techniques is crucial, however, to enable the control of this species with minimal impact to the shellfish industry and the wider environment.
Original languageEnglish
PublisherScottish Association for Marine Science
Number of pages19
Publication statusPublished - Dec 2007

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NameSAMS Internal reports


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