Subtidal Rock

Subtidal rock habitats comprise bedrock, boulders and cobbles occurring below low water mark. The communities found here are strongly affected by the availability of light; shallow areas are typically dominated by seaweeds and in deeper areas below the photic zone (about 50m) communities comprise exclusively animals. Other factors influence the composition of communities including wave action, tidal stream strength and salinity.

Seaweed communities are dominated by several species of large kelp, Laminaria digitata, Laminaria hyperborea and Laminaria saccharina. On the east coast of Scotland in the more turbid waters of the North Sea these may extend down only a few metres before a more sparse community of small foliose and encrusting red seaweeds take over. On the outer west coast, and especially on some of the more remote islands such as St Kilda, the kelp can extend down to depths in excess of 40m.

On the east coast of Scotland subtidal rock is rare and occurs only in isolated pockets. There is much more on the west coast with many of the sea lochs having extensive areas of bedrock extending to considerable depths. There are also extensive areas of bedrock to the west of the Hebrides and around Shetland. The extensive, relatively shallow bedrock to the west of the Hebrides support a dense kelp forest that is important in dissipating a lot of wave energy, thus protecting the vulnerable west facing coasts of the Outer Hebrides from erosion.