Grazed, mixed Laminaria hyperborea and Laminaria saccharina on sheltered Atlantic infralittoral rock

Description (English)

Silted infralittoral rock with mixed Laminaria hyperborea and Laminaria saccharina kelp forest, intensively grazed by the echinoderm Echinus esculentus and the gastropods Gibbula cineraria and Calliostoma zizyphinum. Although both kelp species can occur in equal abundance (Common), L. hyperborea usually dominates. The grazing-resistant brown seaweed Desmarestia aculeata and Cutleria multifida may be present. A similar variety of red seaweeds to those found in the ungrazed kelp forest (MB1-2391) may occur beneath the kelp canopy, but in much lower abundance. As grazing intensity increases the seaweed cover decreases - and some sites are reduced to the bare appearance of encrusting brown and coralline algae beneath the kelp canopy. The L. hyperborea stipes generally support more seaweeds than the rock beneath, including Cryptopleura ramosa, Delesseria sanguinea, Phycodrys rubens and Bonnemaisonia hamifera. The stipes may also support sometimes dense ascidians Clavelina lepadiformis and Ciona intestinalis and the echinoderm Antedon bifida. The kelp fronds are often densely covered by the hydroid Obelia geniculata. At the most intensively grazed sites even the kelp stipes are bare. Although the rock appears bare, between boulders and in crevices there are often the brittlestar Ophiothrix fragilis and the crabs Necora puber and Pagurus bernhardus. The tube-building Pomatoceros triqueter and bryozoan crusts are commonly found on any vertical surfaces.
Situation: This biotope can be found in similar conditions as units MB1-2391 and MB1-2392 but where the numbers of grazers present are in high enough numbers to cause substantially community impoverishment through grazing. Generally occurs on isolated rock, surrounded by sediment biotopes. Although it has been recorded from sites astride the ungrazed kelp biotopes (MB1-2391 and MB1-2392) it is more usually found on bedrock or boulder exposures (MC1-21) adjacent to sediment seabed characterised by infaunal species.
Temporal variation: If the grazing pressure is reduced (i.e. a decrease in the number of grazing echinoderms present) the community will eventually re-establish itself as a mixed kelp forest or park (unit MB1-239).

Source: EUNIS habitat classification