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Upper shore hard substratum that is relatively unstable (e.g. soft rock) or subject to considerable freshwater runoff is typically very species poor and characterised by a dense mat of Ulva spp., though Ulva lactuca can occur as well. It occurs in a wider zone spanning from the supralittoral down to the upper eulittoral, across a wide range of wave exposures range. This biotope is generally devoid of fauna, except for occasional limpets Patella vulgata, winkles Littorina littorea or Littorina saxatilis and barnacles Semibalanus balanoides.