Rocky shores, by definition, occur where land and sea meet on a hard substratum. Where there is a considerable tidal range, the shore has an intertidal zone which is subject to cycles of immersion and emersion. Although the habitats and communities under consideration in the present report are often referred to as intertidal, they do not always conform to the strict definition of the term. Tides may be more or less absent in some areas, with characteristic rocky shore species occupying a narrow range which is wetted by waves or swell. As described later in this chapter, some of these species can be found many metres above the highest tide level on exposed cliffs. Biological communities occupying shore levels that experience both exposure to the air and wetting by the sea are described as littoral.

The onshore currents and rising tides supply the shore with particulate organic material, an important food source. Rocky shores are characterised as ‘eroding’. Sediment and debris are removed by waves and retreating tides. Sediment may, however, accumulate in crevices or under dense algal canopies. Wave action usually ensures that rocky shores are well supplied with dissolved oxygen. The shallow waters allow light penetration, so primary production is rarely light limited.

Two major physical gradients (vertical emersion gradient and horizontal wave action gradient) determine the types of community which a shore can support. Physical characteristics of the substratum are also important with increasing complexity leading to greater biodiversity. A number of physical factors relating to the geographical position of the shore also have a strong influence on the biota present.

Physical gradients

Topographical structure of the substratum

Other physical factors

References