Sheltered to extremely sheltered lower eulittoral rock with Fucus serratus (for detailed description of the rich associated community please see unit A1.3151). Two variants of this biotope have been described; - Fully marine conditions (A1.3151) and mixed substrata (A1.3152). Please notice that three other biotopes with a F. serratus dominance have been described: Variable salinity (A1.326), tide-swept (A1.152) and tide-swept on mixed substrata (A1.153). Situation: This biotope usually occurs immediately below a dense canopy of Fucus vesiculosus (A1.313) on sheltered shores or an Ascophyllum nodosum zone (A1.3141) on sheltered shores; consequently low densities of these species may occur in this biotope. The sublittoral fringe below is dominated by the kelps Laminaria saccharina and Laminaria digitata on sheltered shores (A3.3131; A3.3121).