So far the environment has been considered only in terms of
physico-chemical variables, but biological factors can also influence community
composition. Biological interactions will be considered in the following section, but
grazing should be mentioned as it used as a descriptor in the MNCR classification -
'grazed fauna' on moderately exposed circalittoral rock. This grazed fauna is reminiscent
of the scour-tolerant fauna above, including bryozoan crusts, calcareous tubeworms,
hydroids, the anemone Urticina, and the grazing sea urchin Echinus esculantus.