Wireweed (Sargassum muticum)



Wireweed (Sargassum muticum)

Photo courtesy of SNH

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  • Rapid growth rate of up to 10 cm per day, with a long life span of 3-4 years.
  • Reproduces both sexually and via floating fragments. Sexual reproduction releases thousands of “germlings” that settle rapidly.
  • Dense monospecific mats can form very quickly excluding other species.
  • Mats reduce available light for understory species, dampen water flow, increase sedimentation rates and reduce ambient nutrient concentrations available for native species.
  • Natural dispersal.
  • Contaminant of oyster spat.
  • Fouling on boats and other marine equipment.



Has already been found in a number of sites in Scotland with rapid spread recorded in 2008 making prevention difficult.

Physical Control

According to the NNSS factsheet, it may be possible to physically remove individuals from localised areas by hand. Although care must be taken to prevent further spread of the species by detaching and spreading new, fertile sections. It is essential to remove the entire holdfast to prevent new growth. Recolonisation from surrounding populations following clearance is likely.

Chemical Control

None known

Biological Control

None known



Non Native Species Secretariat identification guide

Non Native Species Secretariat Fact Sheet

SNH Species Action Framework

Invasive Species Ireland Fact Sheet

Daisie Species Fact Sheet

Global Invasive Species Database

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