Biodiversity & Conservation

Wireweed - Sargassum muticum

Sargassum muticum

Image Keith Hiscock - Sargassum muticum, North Devon. Image width ca XX cm.
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Distribution map

Sargassum muticum recorded (dark blue bullet) and expected (light blue bullet) distribution in Britain and Ireland (see below)

Why do the maps differ?

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Sargassum muticum is not listed under any importance categories.

Taxonomy icon Taxonomy Taxon English term
Phylum Ochrophyta Brown and yellow-green seaweeds
Class Phaeophyceae
Authority (Yendo) Fensholt
Recent synonyms None
Map icon Recorded Distribution in Britain and Ireland Sargassum muticum has spread along the south coast to the Isles of Scilly and along the north Cornish coast to Lundy. Populations have also been recorded in Strangford Lough, Northern Ireland and Loch Ryan and the Firth of Clyde, Scotland.
Habitat information icon Habitat information Grows on hard substrata in shallow waters and can also tolerate estuarine conditions. It can out-compete local species because it is fast growing, can reproduce within the first year of life and being monoecious can fertilize itself.
Text page icon Description A large brown seaweed (with a frond often over 1m long), the stem has regularly alternating branches with flattened oval blades and spherical gas bladders. It is highly distinctive and olive-brown in colour. Wireweed is an invasive species from the Pacific that appeared on the Isle of Wight in 1973, having spread to Britain from France. It competes with native species such as seagrasses and is considered a nuisance in harbours, beaches and shallow waters.
Identifying features
  • Fronds often more than 1 m in length.
  • Olive-brown in colour.
  • Regular alternating branches along stem.
  • Flattened oval blades and spherical gas bladders along branches.
Additional information icon Additional information Sargassum muticum is also known as 'Japweed' and 'Japanese weed'.

This review can be cited as follows:

Paolo Pizzolla 2008. Sargassum muticum. Wireweed. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 20/06/2013]. Available from: <http://www.marlin.ac.uk/speciesinformation.php?speciesID=4296>