Rhodothamniella floridula on sand-scoured lower eulittoral rock

Description (English)

Lower eulittoral and sublittoral fringe bedrock and boulders subject to mild sand-scouring characterised by a canopy of the wracks Fucus serratus or Fucus vesiculosus, beneath which a mat of the sand-binding red seaweed Rhodothamniella floridula occurs. These mats can form distinct areas without F. serratus. The small hummocks of R. floridula also contain a diversity of other red seaweeds tolerant of sand scour, e.g. Palmaria palmata, Chondrus crispus, coralline crusts and Mastocarpus stellatus. The brown seaweed Cladostephus spongiosus or the ephemeral green seaweed Enteromorpha intestinalis, Ulva lactuca or Cladophora rupestris may occur. The hydroid Dynamena pumila can form colonies on the F. serratus fronds. The barnacle Semibalanus balanoides, the limpet Patella vulgata, the anemone Actinia equina and the polychaete Pomatoceros triqueter may be present where bedrock are available along with a few winkles such as Littorina littorea. In addition, polychaetes and amphipods may burrow into the R. floridula mat, while the mussel Mytilus edulis is restricted to small crevices in the bedrock. The species diversity of this biotope is normally low and there can be much variation in the species composition from site to site.
Situation: Above this biotope in sand influenced areas are a community dominated by M. edulis and F. vesiculosus or where the sand scour is more severe, is a biotope dominated by ephemeral seaweeds such as Enteromorpha spp. and the red seaweed Porphyra spp. (unit A1.452). Below this biotope are biotopes dominated by F. serratus and/or red seaweeds (see subunits of A1.214) or biotopes dominated by kelp such as Alaria esculenta and/or Laminaria digitata (A3.1112).
Temporal variation: Where sand scour is more severe, fucoids and R. floridula may be rare or absent and green ephemeral seaweeds dominate the substratum (unit A1.452).

Source: EUNIS habitat classification