Description of biotope or habitat type

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   Saccharina latissima forest on very sheltered upper infralittoral rock

Description

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 pseudoceranoïdes, Cystoclonium purpureum, Rhodophyllis divaricata, Ceramium nodulosum and Polyneura bonnemaisonii typically occur.

Situation

Although this biotope may occur below a mixed kelp canopy that occupies the sublittoral fringe (Lsac.Ldig or Ldig.Ldig) at some sites it extends directly into the sublittoral fringe and abuts the F. serratus zone (Fserr or FserX on mixed substrata). Where suitable hard substrata are available, the L. saccharina diminishes in abundance (typically Frequent) with increasing depth to form kelp park (Lsac.Pk).

Temporal variation

Unknown

Characterising species

Similar biotopes or habitat types

IR.LIR.K.SLat.Pk

S. latissima is sparse (Occasional) and far fewer red seaweeds occur, also in low abundance.

IR.LIR.K.LhypSlat.Ft

This biotope occurs in similar conditions as IR.LIR.K.Slat.Ft, but is generally less silted. It is dominated by the kelp L. hyperborea (Abundant) and has a lower abundance of S. latissima (Common) than IR.LIR.K.Slat.Ft. There tends to be a greater variety of species, particularly more red seaweeds in IR.LIR.K.LhypSlat.Ft.

IR.LIR.K.Slat.Gz

The variety of red seaweeds is reduced where grazers such as the urchin E. esculentus (Frequent) and the brittlestar Ophiothrix fragilis (Occasional) are present in high numbers. Grazing pressure can reduce the rock beneath the kelp canopy to coralline encrusted rock, with only a few tufts of foliose seaweeds present.

IR.LIR.KVS.SlatPsaVS

This biotope occurs at slightly more sheltered shores (Very to Extremely sheltered) with reduced salinity. The depauperate coralline-encrusted rock supports few foliose red seaweeds due to the high numbers of the urchins E. esculentus and Psammechinus miliaris.

IR.LIR.KVS.SlatPhyVS

Reduced salinity with filamentous green seaweeds.

Classification history of this biotope or habitat type