Walls, or massive boulders, in caves or gullies that are subject to severe wave-surge and characterised by extensive thin crusts of the sponge Halichondria panicea with smaller patches of other sponges such as Esperiopsis fucorum or Clathrina coriacea. Small turfs of robust hydroids, such as Diphasia rosacea and Ventromma halecioides, and patches of the barnacle Balanus crenatus, coralline crusts and tube-building spirorbid polychaetes may be present. The starfish Henricia spp., the brittlestar Ophiopholis aculeata and the crabs Cancer pagurus and Necora puber can be present. The anemones Sagartia elegans, Urticina felina and Actinia equina can be found in cracks and crevices or under boulders. The mussel Mytilus edulis may be present in low densities. Situation: This surge-tolerant biotope of low-growing fauna is typically confined to the mid or rear section of caves (or the narrowest part of gullies) where the wave-surge is intensified. It generally abuts the less surged ascidian-sponge communities (units A3.712, A3.714 and A3.713). A highly scoured zone of barnacles and calcareous tubeworms often form a zone below, abutting the cave/gully floor (A3.7161).