Description of [Caryophyllia smithii] with faunal and algal crusts on moderately wave-exposed circalittoral rock
This variant is typically found on the upper and vertical faces of exposed and moderately wave-exposed circalittoral rock, subject to very little water movement. Where this variant is found on slightly more wave-exposed sites, it tends to be found towards the bottom of its depth range. The rocky substratum has a grazed appearance, with encrusting red algae. Diversity of species is very low, possibly due to grazing pressure from the sea urchin Echinus esculentus. From afar, there is little evident epifauna attached to the rocks apart from the white, calcareous tubes of the polychaete Pomatoceros triqueter and the cup-coral Caryophyllia smithii. In addition, bryozoan crusts such as Parasmittina trispinosa are frequently seen. Under closer inspection, a few more species become apparent but few are typically characterising of this particular variant. The echinoderms Antedon bifida, Asterias rubens, Ophiothrix fragilis, Marthasterias glacialis, Ophiocomina nigra and Crossaster papposus are occasionally present. Sparse clumps of hydroids such as Halecium halecinum, Kirchenpaueria pinnata and Nemertesia antennina may be found attached to rocky outcrops or boulders. Small specimens of Alcyonium digitatum may be present. The ascidians Ciona intestinalis, Clavelina lepadiformis and Ascidia mentula also occur in this variant but are found in greater numbers in other biotopes. The top shells Calliostoma zizyphinum, Gibbula cineraria, and the saddle oyster Pododesmus patelliformis may be seen on the rock surface whilst the crab Cancer pagurus may be seen under boulders and in crevices. The anemone Metridium senile may be found under rocky overhangs and on the sides of boulders. Situation: As A4.2146 occurs on moderately wave-exposed coasts, kelp forests in the infralittoral zone shallower than this variant tend to be dominated by robust kelp species such as Laminaria hyperborea (unit A3.214) and Saccorhiza polyschides. Immediately below A4.2146 (typically bedrock/boulder substratum), sublittoral sediment biotopes such as muddy sands, containing Nephrops norvegicus, Virgularia mirabilis and Funiculina quadrangularis are found. Occasionally, biotopes composed of coarser sand/gravelly material may be present, with species such as Peachea cylindrica and Neopentadactyla mixta. When wave exposure and tidal stream increase, A4.2146 tends to grade into A4.2145.