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This biotope is typically found on the vertical and upper faces of strongly tide-swept, wave-exposed circalittoral bedrock and boulders. It is characterised by a dense carpet of the robust hydroid Tubularia indivisa. The barnacle Balanus crenatus, where present, is recorded as common. The accompanying species in the community are determined by tidal stream strength. On the more sheltered sides of headlands, where tidal streams are accelerated, sponges such as Pachymatisma johnstonia, Amphilectus fucorum, Myxilla incrustans and Halichondria panicea proliferate forming the CTub.CuSp sub-biotope. There may also be a scattered bryozoan turf, formed by criisid bryozoans. However, where tidal streams are slightly reduced, but on more wave-exposed coasts, anthozoans such as Alcyonium digitatum become more prominent forming the CTub.Adig biotope. Other species recorded in this biotope include the anemones Cylista elegans, Actinothoe sphyrodeta, Corynactis virdis and Urticina felina. There may be scattered clumps of hydroids such as Sertularia argentea and Nemertesia antennina. Where `relative shelter' is afforded by the topography of the seabed, the bryozoans Flustra foliacea, Alcyonidium diaphanum and the crab Cancer pagurus may be found. More ubiqutous species such as Asterias rubens and Calliostoma zizyphinum may also be present.

This variant is typically found on the vertical and upper faces of strongly tide-swept, exposed circalittoral bedrock and boulders. It is commonly associated with areas where turbidity levels are high for much of the year, for example, around Anglesey and the Lleyn Penisula. From afar, this variant appears as a dense carpet of Tubularia indivisa covering tide-swept gully walls, floors and boulders. T. indivisa is frequently observed growing through sheets of sponges such as Myxilla incrustans and Halichondria panicea as well as through dense patches of the barnacle Balanus crenatus and tubes of the amphipod Jassa spp. Several other species of sponge appear to be tolerant of the high turbidity in areas where this variant occurs, many of which are common in other biotopes. These include Amphilectus fucorum, Pachymatisma johnstonia, Hemimycale columella, Dysidea fragilis and Clathrina coriacea. Robust hydroids (other than T. indivisa) such as Nemertesia antennina and Sertularia argentea occur in patches. The anemones Urticina felina, Actinothoe sphyrodeta and Cylista elegans are typically common. A short bryozoan turf consisting of crisiid bryozoans, Alcyonidium diaphanum, Bicellariella ciliata, Bugulina turbinata and Bugulina flabellata may be present. Alcyonium digitatum may occasionally be seen although it doesn't tend to be as dominant as in CTub.Adig. Individual Corynactis viridis may be seen scattered across the gully walls and boulders. The starfish Henricia oculata may be seen on boulders and gully floors whilst typical under-boulder fauna includes the crab Cancer pagurus.

This variant is typically found on exposed circalittoral bedrock and boulders in sounds, narrows and around tide-swept promontories in accelerated tidal streams. It is dominated by aggregations of dead man's fingers Alcyonium digitatum, and dense clumps or continuous cover of the robust hydroid Tubularia indivisa, particularly on prominent ledges and ridges. Anemones such as Cylista elegans, Urticina felina, Metridium senile, Actinothoe sphyrodeta and Corynactis virdis form a prominent component of the community. Occasionally, massive sponges such as Pachymatisma johnstonia and Amphilectus fucorum may be present. Encrusting species such as the polychaete Spirobranchus triqueter and the barnacle Balanus crenatus may be dotted around the rocks, and the top shell Calliostoma zizyphinum may also be observed. Clumps of the bryozoan Flustra foliacea are occasionally seen. The starfish Asterias rubens may be seen amongst a patchy turf of Crisia denticulata and the bryozoan Alcyonidium diaphanum. This variant may also be found on tideswept wrecks and other artificial sustratum.