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Marine Habitat Classification

Description of biotope or habitat type

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   Sargassum muticum on shallow slightly tide-swept infralittoral mixed substrata

Physical habitat description

Salinity Full (30-35 ppt)
Wave exposure Sheltered, Very sheltered, Extremely sheltered
Tidal streams Moderately strong (1-3 kn)
Substratum Mixed substrata
Zone Infralittoral - upper, Sublittoral fringe
Depth Band 0-5 m
Other Features

Download comparative physical and biological data. The comparative tables enable a rapid comparison of the species composition and principal physical characteristics between a given set of biotopes.

Distribution of habitat IR.LIR.K.Sar <I>Sargassum muticum</I> on shallow slightly tide-swept infralittoral mixed substrata

  • Records used to define the biotope (core records)
  • Other records assigned to this biotope, marked as 'certain'
  • Other records assigned to this biotope, marked as 'uncertain'
  • Predicted extent of the level 3 (for sublittoral rock & deep sea) or 4 (for sublittoral sediment) habitat

Point data based on records in the UK Marine Recorder Snapshot. Predicted habitat extent is from UKSeaMap.


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 substrata (typically 0-10% bedrock on 90-100% sandy sediment). The substrate on which this S. 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, S. 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 S. 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). S. muticum is also found on hard, bedrock substrates within L. saccharina canopies. S. muticum plants on hard substrate area, under a dense L. saccharina 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 Carradoriella elongata and the green seaweeds Cladophora sp., Ulva lactuca and Bryopsis plumosa. The anthozoan Anemonia viridis and the crab Necora puber can be present. More information is necessary to validate this description.


Where there is a greater proportion of bedrock or boulders (15-100%) L. saccharina will typically dominate the canopy. Areas with pebble cover on a hard substrate are colonised by S. muticum, but individuals quickly become peripatetic and are lost.

Temporal variation


Characterising species

Taxon Relative importance of taxon for defining this community (%) Typical abundance - SACFOR scale % of core records where taxon was recorded
Sargassum muticum 33 Common 81-100%
Gracilaria gracilis 13 Frequent 61-80%
Saccharina latissima 13 Frequent 61-80%
Ceramium nodulosum 9 Occasional 61-80%
Chylocladia verticillata 4 Occasional 41-60%
Anemonia viridis 3 Rare 41-60%
Ulva lactuca 3 Frequent 41-60%
Bryopsis plumosa 2 Occasional 21-40%
Chorda filum 2 Occasional 21-40%
Cladophora 1 Occasional 21-40%
Cliona celata 1 21-40%
Treptacantha baccata 1 Occasional 21-40%
Necora puber 1 Occasional 21-40%
Carradoriella elongata 1 Rare 21-40%
Pterothamnion plumula 1 Occasional 21-40%

Similar biotopes or habitat types

Not applicable or unknown.

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