Skip to Content

Marine Habitat Classification


Description of biotope or habitat type

To understand more about what this page is describing, see How to use the classification. See also How to cite.

   Grazed Laminaria hyperborea forest with coralline crusts on upper infralittoral rock


Habitat (physical) description

Salinity Full (30-35 ppt)
Wave exposure Exposed, Moderately exposed
Tidal streams Moderately strong (1-3 kn), Weak (>1 kn)
Substratum Bedrock; large boulders
Zone Infralittoral - upper
Depth Band 0-5 m, 5-10 m, 10-20 m
Other Features Urchin grazing

Download comparative physical and biological data. The comparative tables enable a rapid comparison of the species composition and principal physical characteristics between a given set of biotopes.

Distribution of habitat IR.MIR.KR.Lhyp.GzFt Grazed <I>Laminaria hyperborea</I> forest with coralline crusts on upper infralittoral rock

  • Records used to define the biotope (core records)
  • Other records assigned to this biotope, marked as 'certain'
  • Other records assigned to this biotope, marked as 'uncertain'
  • Predicted extent of the level 3 (for sublittoral rock & deep sea) or 4 (for sublittoral sediment) habitat

Point data based on records in the UK Marine Recorder Snapshot. Predicted habitat extent is from UKSeaMap.

Description

Exposed to moderately exposed Laminaria hyperborea forest is in some areas intensely grazed by the urchin Echinus esculentus. The rock surface lacks a significant turf of foliose seaweeds and generally looks bare, though encrusting algae cover the rock. In addition to these encrusting coralline algae, non-calcareous crusts such as Cruoria pellita and brown algal crusts also occur. The kelp stipes may or may not be grazed; in the most extremely grazed areas, the stipes are also devoid of seaweeds. More usually, however, the stipes offers a refuge from grazing, and are characterised by dense turfs of red seaweeds, especially Phycodrys rubens, Callophyllis laciniata, Plocamium cartilagineum and Delesseria sanguinea. The hydroid Obelia geniculata and the bryozoan Membranipora membranacea colonise the kelp fronds. On the rock itself certain brown seaweeds such as Cutleria multifida may persist in this grazed environment. Fast-growing species such as the kelp Laminaria saccharina may be present at sites recovering from grazing, opportunistically colonising the rock surfaces that have been cleared by grazing. The fauna within a grazed kelp forest is also relatively sparse and is mostly confined to cracks, crevices and under-boulders. Species such as the ascidian Clavelina lepadiformis can often be found on vertical rock. Also found on the rock surface are the anthozoans Urticina felina and Alcyonium digitatum. Encrusting species such as the tube-building polychaete Pomatoceros triqueter are resistant to grazing and may occur in abundance. The grazers present include the echinoderm Echinus esculentus and the gastropods Calliostoma zizyphinum and Gibbula cineraria. Other echinoderms present include Asterias rubens and Antedon bifida which can be abundant in the north-west. Moderate grazing occurs within many kelp forests; records should only be assigned to this biotope where the community has been intensively grazed leaving algal-encrusted rock with very few epilithic algae.

Situation

With increasing depth, the kelp forest grades into a grazed kelp park (Lhyp.GzPk), the lower limit of which is often abrupt, representing the balance point between urchin-grazing pressure and kelp growth capabilities. In wave-exposed steep rocky areas, the shallowest water may be characterised by a forest of kelp with red seaweeds (LhypR.Ft), with a grazed kelp forest beneath. This effect may be a result of the increased wave action in shallower water, which regularly dislodges the urchins thereby reducing their grazing impact. Lhyp.GzFt is prevalent in the north of the UK where E. esculentus populations reach high densities. Although E. esculentus is widely distributed around the UK it occurs in greatest abundance in Scotland and north-east England where urchin grazing can substantially affect infralittoral communities.

Temporal variation

Fluctuations in E. esculentus numbers may give foliose seaweeds a chance to re-grow periodically. Further information is required on the temporal variation within these grazed forests and the changes in community structure when grazing pressure decreases.

Characterising Species

Taxon Relative importance of taxon for defining this community (%) Typical abundance - SACFOR scale % of core records where taxon was recorded
Obelia geniculata 1 Frequent 21-40 %
Alcyonium digitatum 2 Occasional 41-60 %
Urticina felina 1 Occasional 41-60 %
Pomatoceros triqueter 5 Frequent 41-60 %
Gibbula cineraria 2 Occasional 41-60 %
Calliostoma zizyphinum 2 Occasional 41-60 %
Membranipora membranacea 1 Frequent 21-40 %
Antedon bifida 1 Occasional 21-40 %
Asterias rubens 5 Occasional 61-80 %
Echinus esculentus 15 Common 81-100 %
Corallinaceae 12 Abundant 61-80 %
Plocamium cartilagineum 1 Frequent 21-40 %
Delesseria sanguinea 1 Occasional 41-60 %
Phycodrys rubens 4 Frequent 61-80 %
Cutleria multifida 3 Common 21-40 %
Laminaria hyperborea 20 Abundant 81-100 %

Similar biotopes

IR.MIR.KR.Lhyp.GzPk
Found beneath the kelp forest and has a lower abundance of kelps but similar species composition to kelp forest.

IR.HIR.KSed.XKScrR
Bare rock surfaces beneath the kelp canopy may also be caused by sand-scour and should not be confused with the barren appearance of a community decimated (reduced) by grazing.

Photos

IR.MIR.KR.Lhyp.GzFt Grazed Laminaria hyperborea forest with coralline crusts on upper infralittoral rock, NW of Hoxa Head, Scapa Flow. Sue Scott © JNCC
IR.MIR.KR.Lhyp.GzFt Grazed Laminaria hyperborea forest with coralline crusts on upper infralittoral rock, NW of Hoxa Head, Scapa Flow. Sue Scott © JNCC
IR.MIR.KR.Lhyp.GzFt Grazed Laminaria hyperborea forest with coralline crusts on upper infralittoral rock, Point of Oride, West Voe, Shetland. Keith Hiscock © JNCC
IR.MIR.KR.Lhyp.GzFt Grazed Laminaria hyperborea forest with coralline crusts on upper infralittoral rock, Point of Oride, West Voe, Shetland. Keith Hiscock © JNCC

Back to top