information on the biology of species and the ecology of habitats found around the coasts and seas of the British Isles

Sargassum muticum on shallow slightly tide-swept infralittoral mixed substrata



UK and Ireland classification

UK and Ireland classification


Mixed substrata from the sublittoral fringe to 5m below chart datum dominated by the brown seaweed Sargassum muticum.  This invasive non-native brown seaweed can form a dense canopy on areas of mixed substratum (typically 0-10 % bedrock on 90-100 % sandy sediment).  The substrate on which this Sargassum muticum dominated community is able to develop is highly variable, but particularly prevalent on broken rock and pebbles anchored in sandy sediment.  The pebbles, cobbles and broken bedrock provide a substrate for alga such as the kelp Saccharina latissima.  During the spring, Sargassum muticum has large quantities of epiphytic ectocarpales and may also support some epifauna e.g. the hydroid Obelia geniculata commonly found on kelp.  The brown seaweed Chorda filum, which thrives well on these mixed substrata, is also commonly found with Sargassum muticum during the summer months.  In Strangford Lough, where this biotope occurs, the amphipod Dexamine spinosa has been recorded to dominate the epiphytic fauna (this is known to be commonly found in Zostera spp. beds).  Sargassum muticum is also found on hard, bedrock substrates within Saccharina latissima canopies.  Sargassum muticum plants on hard substrate area, under a dense Saccharina latissima canopy, are typically smaller and at a much lower density, especially where a lush, under-storey exists with red seaweeds such as Ceramium nodolosum, Gracilaria gracilis, Chylocladia verticillata, Pterosiphonia plumula and Polysiphonia elongata and the green seaweeds Cladophora sp., Ulva lactuca and Bryopsis plumosa.  The anthozoan Anemonia viridis and the crab Necora puber can be present.  Information taken from Connor et al. (2004) however more information is necessary to validate this description.

Depth range

0-5 m

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Species indicative of sensitivity


Physical Pressures

No sensitivity data available

Chemical Pressures

No sensitivity data available

Biological Pressures

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This review can be cited as:

Perry, F. & Tillin, H.M., 2015. [Sargassum muticum] on shallow slightly tide-swept infralittoral mixed substrata. In Tyler-Walters H. and Hiscock K. (eds) Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 18-06-2018]. Available from:

Last Updated: 14/12/2015