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Overhanging shaded bedrock on the open lower shore and at the entrance to inner reaches of caves (where light availability permits), which is not subject to appreciable wave-surge, characterised by a shade-tolerant red seaweed community. It includes foliose species such as Plumaria plumosa, Palmaria palmata, Mastocarpus stellatus, Membranoptera alata and Osmundea pinnatifida, but Lomentaria articulata and coralline crusts are usually present as well. The foliose green seaweed Ulva lactuca can be present. The rock surface often supports dense populations of calcareous tube-forming polychaetes Spirorbis spp. and Spirobranchus spp., while sponges such as Grantia compressa, Halichondria panicea and Hymeniacidon perlevis can be common. The hydroid Dynamena pumila (normally found on fucoids) hangs in distinct form from overhanging rock. Colonies of the ascidian Botryllus schlosseri can be found on the rock, along with the mussel Mytilus edulis and the barnacles Semibalanus balanoides and Perforatus perforatus (the latter may occur at high densities in the south and west), while the anemone Actinia equina thrives in the permanently damp pits and crevices. The whelk Nucella lapillus can be found among the barnacles and mussels, preying on them. The long list of characterising species is partly due to the difference in the species composition and does not solely reflect a high species richness.

Overhanging, and shaded vertical, bedrock on the lower shore and in lower shore caves, which is not subject to appreciable wave-surge, characterised by crusts of bryozoans including Oshurkovia littoralis, sponges such as Grantia compressa, Halichondria panicea, Sycon ciliatum and Hymeniacidon perlevis and the ascidian Botryllus schlosseri. On overhangs, the hydroid Dynamena pumila hangs in distinct form from overhanging rock. The barnacles Balanus crenatus, Perforatus perforatus (sometimes at high densities) and Semibalanus balanoides, and the calcareous tube-forming polychaetes Spirorbis spp. and Spirobranchus triqueter can be present as well. Certain species which are generally confined to the sublittoral, including the anemones Metridium senile and Corynactis viridis, may be found in the lower shore caves and overhangs. Littoral species such as Actinia equina are also present. The only algae present are coralline crusts. The list of characterising species partly reflects the variation in the species composition between individual overhangs and caves although this biotope can have a high species richness.

Orange, brownish or blackish gelatinous bands of algae at high tide and supralittoral levels on open cliff faces and on upper walls and ceilings at entrances and to the rear of upper and mid-shore hard and soft rock (chalk) caves. This dark brown band consists of an assemblage of Haptophyceae such as Apistonema spp., Pleurochrysis carterae and the orange Chrysotila lamellosa, but other genera and species of Chrysophyceae, Haptophyceae and Prasinophyceae are likely to be present as well. Species such as Entodesmis maritima and Thallochrysis littoralis and the filamentous green alga Epicladia perforans are often associated with Apistonema spp. and the latter can form a green layer beneath the Apistonema spp. Associated with this splash zone algal community is an assemblage of animals of terrestrial origin, with red mites, insects and centipedes commonly found. These species descend into the community as the tide falls and retreat as the tide rises. The most common truly 'marine' species is the small winkle Melarhaphe neritoides.

Where caves and overhangs occur on rocky shores, the shaded nature of the habitat diminishes the amount of desiccation suffered by biota during periods of low tides which allows certain species to proliferate. In addition, the amount of scour, wave surge, sea spray and penetrating light determines the unique community assemblages found in upper, mid and lower shore caves and overhangs on the lower shore. Biotopes from the surrounding shore such as MytB, Sem or any of the fucoid communities occasionally extend into cave entrances. Sem often extends some way into the cave. Other open shore biotopes may also be found within caves, such as the green seaweed Prasiola stipitata on cave roofs where birds roost (Pra), and localised patches of green algae where freshwater seepage influences the rock (Ent). Rockpools containing encrusting coralline algae (Cor), fucoids and kelp (FK) and hydroids and littorinid molluscs may occur also on the floor of cave entrances. The cave biotope descriptions are largely based on data obtained from surveys of Berwickshire caves (ERT,2000), chalk caves from the Thanet coast (Tittley et al, 1998; Tittley & Spurrier 2001) and data from Wales (CCW Phase 1 data). In general, the biomass and diversity of algal species found in upper and mid-shore littoral caves decreases with increasing depth into the cave as the light levels diminish. Fucoids are usually only found at the entrances to caves, but red algae, and filamentous and encrusting green algae are able to penetrate to lower light intensities towards the back of the cave, and mats of the turf forming red seaweed Rhodochorton purpureum and/or patches of the green seaweed Cladophora rupestris may occur on the upper walls (AudCla). Brownish velvety growths of the brown algae Pleurocladia lacustris occurring in mats with the red alga A. purpurea on cave walls and upper littoral levels of cliffs (AudPil) should not be confused with the green (GCv) or golden brown algal stains often found above this zone on the ceilings of the caves (AudPil; ChrHap). Below is a zone of Verrucaria mucosa and/or Hildenbrandia rubra on the inner and outer reaches (VmucHil). Fauna usually only occur on the lower and mid walls of the caves and generally comprise barnacles, anemones and tube-forming polychaetes (ScrFa; FaCr) depending on the level of boulder scour or wave surge. Where the floors of caves consist of mobile cobbles and small boulders, little algae and fauna occur due to the effects of scouring (BarCv). Vertical or steeply sloping cave walls and overhangs on the mid and lower shore, subject to wave-surge but without scour, support a rich biota of sponges, hydroids, ascidians and shade-tolerant red algae (SByAs, SR or SR.Den).

The upper walls and ceilings of upper and mid-shore hard and soft rock (chalk) dominated by a band of green algal films (or 'stains'). Other encrusting algae including the non-calcified Hildenbrandia rubra may be present. In chalk caves, on the east and south-east coasts of England, a distinctive assemblage of species occurs, including the brown alga Pleurocladia lacustris and the bright green algae Pseudendoclonium submarinum and Epicladia perforans that often covers the cave ceilings. Fauna is generally sparse and limited to limpets such as Patella vulgata and the winkle Littorina saxatilis. The species forming a green algal film that covers upper shore caves in Berwickshire were not identified. More information required to validate this biotope description.

Golden brown velvety growths of the brown algae Pleurocladia lacustris occurring in mats with the red alga Rhodochorton purpureum forming on cave walls and upper littoral levels of cliffs. Fauna is sparse and limited to occasional individuals of the winkle Littorina saxatilis and spirorbid polychaetes. This assemblage is thought to be is widespread throughout Britain, although there are currently few records available. More information are needed to validate this description, which is based on information from the Thanet intertidal survey (Tittley et al. 2004). Received after deadline: A. purpurea has changed name to Rhodochorton purpurea and P. maritima has changed name to Pleurocladia lacustris.

The upper walls and ceilings of the entrances and inner reaches of upper shore caves affected by direct wave action (and therefore moistened by sea spray), characterised by a mosaic of the olive green lichen Verrucaria mucosa and the non-calcified encrusting red alga Hildenbrandia rubra. The black lichen Verrucaria maura and red coralline algae can be present, though not dominating. The fauna in these upper shore caves is generally limited, due to problems of desiccation. However, where conditions remain sufficiently moist, and particularly in crevices and fissures, the barnacle Semibalanus balanoides, the limpet Patella vulgata and winkles Littorina saxatilis may occur, particularly towards the rear of the cave. Although the characterising species of this biotope also occur on the shore, they do not generally occur in a distinct band other than in moist dark caves. The turf-forming red seaweed Rhodochorton purpureum may occasionally occur in low abundance (where A. purpurea covers an extensive area, generally on softer rock such as chalk, the biotope should be recorded as AudCla).

Vertical and steeply-sloping upper walls at the entrances and inner reaches of upper to mid-shore caves that are partially sheltered from direct wave action characterised by a turf of the 'velvety' red seaweed Rhodochorton purpureum. Patches of green filamentous seaweed Cladophora rupestris can be present. The fauna is generally limited to limpets Patella spp., the winkle Littorina saxatilis and the barnacle Semibalanus balanoides, while they usually occur in low abundance. Filamentous or crust forming brown seaweeds may occur mixed with A. purpurea, often becoming a zone in its own right (AudPil) above the AudCrup biotope. Other shade-tolerant red seaweed such as Catenella caespitosa and Lomentaria articulata may occur (but at lower abundance), and where freshwater seepage occurs, Ulva intestinalis can form patches. Some variation in the species composition of the individual caves must be expected depending on local conditions. A. purpurea can be the only seaweed present in caves on the Thanet coast in south-east England. This biotope is known to occur in hard rock caves in north-east England and chalk caves in south-east England. Received after deadline: A. purpurea has changed name to Rhodochorton purpurea.

The inner walls of caves, predominantly in the mid shore in wave-surged conditions dominated by barnacles Semibalanus balanoides, and Verruca stroemia, with patches of encrusting sponges such as Halichondria panicea and Grantia compressa and occasional patches of the mussel Mytilus edulis. Increased moisture allows a denser faunal population than ScrFa to develop within the cave. The limpet Patella vulgata and spirorbid tube-forming polychaetes can be present. The hydroid Dynamena pumila and anemones such as Metridium senile and Actinia equina may occur towards the lower reaches of the cave. Where a dense faunal turf of barnacles or bryozoan crusts covers the cave walls, the biotope can also extend to cover the ceiling and may be accompanied by the bryozoan Alcyonidium diaphanum. Variations of this biotope may occur in mid and lower shore scoured caves in south Wales the rock is dominated by dense Sabellaria alveolata. In south-west England the rock can be completely covered by the barnacle Perforatus perforatus. There may be a variation in the species composition from cave to cave, depending on local conditions.

Upper to lower shore sand- or pebble-scoured cave walls characterised by an impoverished faunal assemblage which may include bryozoan crusts, scattered sponges Halichondria panicea, barnacles such as Semibalanus balanoides or often large Balanus crenatus and the limpet Patella vulgata. The isopod Ligia oceanica may seek refuge in crevices in the rock, and due to the decreased effect of desiccation in these damp caves, other species such as the anemone Actinia equina and spirorbid polychaetes are able to extend further up the shore than normally found on open rock. The lower section of the wall which is subject to greatest scour may be characterised by a band of Spirobranchus triqueter and spirorbid tube-forming polychaetes. In wave sheltered conditions, this biotope may extend to the cave ceiling. The rear of caves on the lower shore may support only sparse fauna consisting of spirorbid polychaetes and barnacles such as Chthamalus montagui with scattered Spirobranchus sp., scattered bryozoan and coralline crusts and in the south-west, occasional Sabellaria alveolata. Shade-tolerant red algae such as Lomentaria articulata may occasionally occur. Due to the low species abundance in this biotope, there may be a variation from cave to cave, depending on local conditions.

Mid and upper shore mobile boulders/cobbles on cave floors and the lower reaches of cave walls which are subject to scour are generally devoid of macro-fauna and flora. However, where light is available around the cave entrances, encrusting coralline algae may cover the rock and boulder surfaces. In some instances they may support sparse fauna such as the limpet Patella spp. and the winkle Littorina saxatilis.

Overhanging bedrock on the lower shore, at cave entrances, to and on inner walls of caves, subject to wave surge and low light levels, and characterised by a high density of small groups of the solitary ascidian Dendrodoa grossularia. The sponges Grantia compressa, Halichondria panicea and Hymeniacidon perlevis are common on the rock surface, while the hydroid Dynamena pumila (normally found on fucoids) hangs in distinct form from overhanging rock. Found on the rock surface are the calcareous tube-forming polychaetes Spirorbis spp. and Spirobranchus spp. along with the barnacles Semibalanus balanoides. The anemone Actinia equina thrives in the permanently damp pits and crevices. Where sufficient light is available a sparse community of shade-tolerant red seaweeds. These include Membranoptera alata, Lomentaria articulata, Audouinella spp. and coralline crusts.