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.

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