Environmental Requirements and Physical Attributes
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.
Topographical structure of the substratum
Other physical factors