Laminaria hyperborea forest with a faunal cushion (sponges and polyclinids) and foliose red seaweeds on very exposed infralittoral rock
|Within Vocab||Marine Habitat Classification for Britain and Ireland Version 97.06|
|Definition||Very exposed and exposed, but wave-surged, upper infralittoral bedrock and massive boulders characterised by a dense forest of the kelp Laminaria hyperborea, beneath which is a rich mixture of sponges, polyclinid ascidians, anemones and dense foliose red seaweeds. The faunal and floral under-storey is generally rich in species due, in part, to the relatively low urchin-grazing pressure in such shallow exposed conditions. The shallowest kelp plants are often short or stunted, while deeper plants are taller with heavily epiphytised stipes. The faunal composition of this biotope varies markedly between sites, but commonly occurring animals are Alcyonium digitatum, Sagartia elegans, Corynactis viridis, the sponges Halichondria panicea and Pachymatisma johnstonia and polyclinid ascidians. Similarly the foliose seaweed turf may show considerable variation. At some sites it can be virtually mono-specific, comprising stands of Delesseria sanguinea, Ptilota plumosa, Cryptopleura ramosa or Plocamium cartilagineum or, in the north, Odonthalia dentata. Other sites may contain a dense mixed turf of these and other species. Beneath the under-storey the rock surface is generally covered with encrusting coralline algae. At sites where the rock is fissured and has many vertical and overhanging surfaces, the fauna is particularly diverse. Large areas of vertical rock are often dominated by Alcyonium digitatum with Metridium senile and or Corynactis viridis (IR.CorMetAlc) and encrusting red algae. This kelp forest most commonly occurs beneath a zone of Alaria/Mytilus (EIR.Ala.Myt) and may contain small patches of Alaria esculenta. At less wave surged sites, or in slightly deeper water beneath this biotope, the kelp forest or park generally lacks the dense faunal turf, and is characterised by kelp and dense red seaweeds (EIR.LhypR.Ft or EIR.LhypR.Pk). In some areas of Shetland the lower infralittoral zone is characterised by a park of L. saccharina and or Saccorhiza polyschides (EIR.LsacSac).|
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