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Very sheltered infralittoral rock dominated by the kelp Saccharina latissima. Typically very silty and often with few associated seaweeds due to siltation, grazing or shading from the dense kelp canopy. The most commonly occurring red seaweeds are Delesseria sanguinea, Phycodrys rubens, Bonnemaisonia hamifera and coralline crusts. In addition to the kelp the brown seaweed Chorda filum and Ectocarpaceae are often present. As well as lacking Laminaria hyperborea, the Lsac biotopes have fewer foliose and filamentous red seaweed species by comparison to LhypLsac biotopes. A depauperate assemblage of animals is present (by comparison to Lhyp.Ft and Lhyp.Pk) predominantly consisting of the encrusting polychaetes Spirobranchus triqueter, the crabs Carcinus maenas and Pagurus bernhardus and the ubiquitous gastropod Steromphala cineraria. The echinoderms Antedon bifida, starfish Asterias rubens, brittlestar Ophiothrix fragilis and urchin Echinus esculentus occur in low abundance. Ascidians are commonly found in all the Lsac biotopes, but the large solitary ascidian Ascidia mentula are most prolific in very sheltered conditions of L. saccharina forests (Lsac.Ft). This biotope is most commonly associated with the sheltered fjordic sealochs of Scotland where sublittoral hard substrata can be found at the sheltered head of the lochs. Similarly the sheltered loughs of Ireland (Lough Hyne, Strangford Lough and Carlingford Lough). It is also found where suitable hard substrata exist in the sheltered inlets of south-west Britain, such as Milford Haven or Plymouth Sound. 4 variants has been described: A mixture of L. saccharina and Laminaria digitata (Lsac.Ldig), dense L. saccharina forest in the upper infralittoral (Lsac.Ft), sparse L. saccharina in the lower infralittoral (Lsac.Pk) and urchin-grazed (Lsac.Gz).

Sheltered bedrock and boulders in the sublittoral fringe characterised by a mixed canopy of the kelp Laminaria digitata (usually in its broad-fronded cape-form) and Saccharina latissima - both species are generally Frequent or greater. Beneath the kelp canopy, the understorey of red seaweeds often includes Chondrus crispus, Dumontia contorta, Bonnemaisonia hamifera and Plocamium cartilagineum. The surface of the rock is usually covered with encrusting coralline algae as well as non-calcified red crusts and the tube-building polychaete Spirobranchus triqueter. The brown seaweeds Chorda filum, Ectocarpaceae and Fucus serratus can be present along with the green seaweeds Ulva lactuca and Ulva intestinalis. Patches of the sponge Halichondria panicea can frequently be found in cracks and crevices. Beneath and between boulders a variety of mobile crustaceans such as Carcinus maenas, the gastropod Steromphala cineraria and the starfish Asterias rubens are common.

Sheltered to extremely sheltered sublittoral fringe and infralittoral bedrock, boulders and cobbles characterised by a dense canopy of the kelp Saccharina latissima. In such sheltered conditions, a distinct sublittoral fringe is not always apparent and this biotope can therefore extend from below the Fucus serratus zone (Fserr) into the upper infralittoral zone, though there may be a mixed L. saccharina and Laminaria digitata zone (Lsac.Ldig) in between. There is a relatively low species diversity and species density due to a combination of heavy siltation of the habitat and the lack of light penetrating through the dense kelp canopy. Only a few species of red seaweeds are present compared with Lsac.Ldig or LhypLsac. The most commonly occurring red seaweeds are Delesseria sanguinea, Phycodrys rubens, Bonnemaisonia hamifera and coralline crusts. Brown seaweeds are also sparse and generally comprise Chorda filum and ectocarpoids. At extremely sheltered sites, where there is a heavy silt cover on the rock and the kelp fronds, the sub-flora is reduced to a few specialised species able to tolerate these conditions, such as the cartilaginous seaweeds Polyides rotunda and Chondrus crispus. Ascidians such as Clavelina lepadiformis, Ascidiella aspersa and Ascidia mentula can remain prominent in such conditions, often occurring on steep or vertical rock which is subject to less siltation. The variety of red seaweeds is further reduced where grazers such as the urchin Echinus esculentus and the top shell Steromphala cineraria are present. The keelworm Spirobranchus triqueter, the crab Carcinus maenas and the hermit crab Pagurus bernhardus can be present. Geographical variations: Northern sites: in sheltered sealochs the most conspicuous fauna in these forests are the large solitary ascidians Ciona intestinalis, Ascidiella spp. and A. mentula which tend to occur in greater abundance than in the mixed kelp forests (LhypLsac). In common with mixed forests, echinoderms are consistently present in low abundance: the featherstar Antedon bifida, common starfish Asterias rubens, the brittlestar Ophiothrix fragilis and the urchin Echinus esculentus are typically present. Saddle oysters Pododesmus patelliformis and chitons Tonicella marmorea can occur in high abundance at some sites. The anthozoan Anemonia viridis is often more prevalent at the extremely sheltered sites. The communities of the sheltered voes and sounds of Shetland and Orkney are similar to those present in the mainland sealochs. Southern sites: Sheltered infralittoral rock is not commonly found outside of the fjordic sealochs. In south-west Britain, where sublittoral rock does occur in shallow marine inlets, the waters are more turbid than in the sealochs, generally limiting kelp to the sublittoral fringe zone. Echinoderms are rare or absent from the south-western L. saccharina forests. A far greater diversity of red seaweeds is associated with the south-western sites: Palmaria palmata, Gracilaria gracilis, Phyllophora pseudocerano??des, Cystoclonium purpureum, Rhodophyllis divaricata, Ceramium nodulosum and Polyneura bonnemaisonii typically occur.

Silty bedrock or boulders with a Saccharina latissima park (often the cape-form). Beneath the canopy, the rock is covered by encrusting coralline algae, and the urchin Echinus esculentus is often present. Due to the amount of silt cover on the rock and the reduced light intensity beneath the broad-fronded kelp, only a few red seaweeds typically survive, the most common species being Phycodrys rubens, Delesseria sanguinea, Bonnemaisonia spp. and Vertebrata byssoides. The brown seaweeds Dictyota dichotoma and Cutleria multifida may be present in low abundance. Compared to the kelp forest zone above (Lsac.Ft) both the kelp and other seaweeds are sparse (Occasional). The most conspicuous animals are large solitary ascidians, particularly Ascidia mentula and Ciona intestinalis, together with the smaller Clavelina lepadiformis. In general, the faunal component of this biotope is similar to other sheltered kelp biotopes and includes a variety of mobile crustaceans such Carcinus maenas and Pagurus bernhardus, the keelworm Spirobranchus spp., terebellid worms, echinoderms Asterias rubens, Ophiothrix fragilis and the featherstar Antedon bifida. The hydroid Kirchenpauria pinnata, although only rare is often found in the kelp park along with the top shell Steromphala cineraria and the barnacle Balanus crenatus.

Coralline encrusted rock with scattered tufts of red seaweed and a relatively high abundance of grazing echinoderms which typically include the urchin Echinus esculentus and/or the brittlestars Ophiothrix fragilis or Ophiocomina nigra. The rock often looks bare, with few conspicuous species present although Saccharina latissima may occur it is generally in low abundance (Rare or Occasional). The red seaweeds, reduced to small tufts through grazing, include Phycodrys rubens, Delesseria sanguinea and Vertebrata byssoides and although these seaweeds also occur in Lsac.Pk they are far less frequent in this biotope. Brown seaweeds, such as Desmarestia viridis, Chorda filum and Cutleria multifida, may be present. Grazing molluscs, such as Steromphala cineraria and can be common. Under-boulder habitats can harbour the crabs Necora puber and Pagurus bernhardus, terebellid polychaetes and the polychaete Spirobranchus spp. with ascidians Ascidia mentula. and Clavelina lepadiformis on the open rock along with the echinoderm Asterias rubens and the hydroids Kirchenpauria pinnata and Obelia dichotoma.