Sheltered to extremely sheltered upper eulittoral bedrock or mixed substrata (boulders, large cobbles or shells on mud) in variable salinity conditions characterised by a band of the spiral wrack Fucus spiralis. The ephemeral green seaweed Enteromorpha intestinalis is usually found in this species poor biotope. The barnacles Semibalanus balanoides and Elminius modestus can be found where suitable substrata are available, while gammarids can be found underneath the fronds of F. spiralis and/or underneath the boulders and cobbles. Also found underneath the fronds and among the boulders are the winkles Littorina saxatilis and Littorina littorea and the crab Carcinus maenas. Situation: This zone usually lies below a zone dominated by the wrack Pelvetia canaliculata (unit A1.311) and occasional clumps of P. canaliculata may be present (usually less than common) amongst the F. spiralis. In areas of extreme shelter and variable salinity conditions (e.g. in Scottish sea lochs), the P. canaliculata and F. spiralis zones often merge together forming a very narrow band. This unit occurs above the wracks Ascophyllum nodosum (A1.324) and/or Fucus vesiculosus (A1.323) zones and these two fucoids may also occur, although F. spiralis always dominates. It can also be found above a zone dominated by the wrack Fucus ceranoides (A1.327). Temporal variation: During the summer months ephemeral green seaweeds such as E. intestinalis can be common.