The wave exposure gradient has a considerable effect on community structure, as a result of the stresses and benefits experienced at different levels of wave energy. Certain species including the barnacles Semibalanus balanoides and Chthamalus montagui are well adapted to survive on exposed shores. Dogwhelks Nucella lapillus, which feed on barnacles, and mussels Mytilus edulis are also more abundant on exposed shores. Algae found on these shores tend to be ephemeral or short turf forms.

The diversity of species on rocky shores increases towards the lower shore where the habitat is wet for longer periods of the day. Only a limited number of species are able to survive on extremely exposed shores, particularly those shores consisting mainly of steep, smooth rock. Protected microhabitats on exposed shores, such as algal turfs or deep crevices, can however support a surprising variety of species (Raffaelli & Hawkins 1996). A major biological influence on community structure is the presence of algal canopies and shorter algal communities at mid and low shore levels. Macroalgae provide a variety of resources which are not available on bare rock. Most importantly, they increase the amount of space available for attachment, they provide shelter from wave action, desiccation and heat and they are an important food source.

Many rocky shore species have a planktonic dispersal phase. These species produce propagules or larvae that spend their early life in the open sea and may eventually settle on shore some distance from where they originated. This strategy allows species to rapidly colonize new areas that become available such as after storms. The level of larval supply and its fluctuations play a considerable role in structuring rocky shore communities and has been appreciated for a long time (Southward & Crisp 1956; Lewis 1964; Kendall et al. 1985).

Macroalgae exude considerable amounts of dissolved organic carbon which are taken up readily by bacteria and may even be taken up directly by some larger invertebrates. Only about 10% of the primary production is directly cropped by herbivores (Raffaelli & Hawkins 1996). On exposed shores, grazers feed mainly on the microbial film. Dissolved organic carbon, algal fragments and microbial film organisms are continually removed by the sea. This may then enter the food chain of local, subtidal ecosystems, or be exported further offshore. Rocky shores also make a contribution to the food of many marine species through the production of planktonic larvae and propagules which supply essential nutrients to pelagic and benthic species.

Semibalanus balanoides, Chthamalus spp., Mytilus edulis.

Fish and crusteaceans migrating into the intertidal zone to feed as the tide rises, are important predators of rocky shore species. Corkwing wrasse Crenilabrus melops rely heavily on the intertidal. Juvenile wrasse are commonly found in rockpools. Shore birds also feed on the rocky shore (Feare & Summers 1985).

Communities on exposed shores show dynamics caused by physical disturbance events, which create space for recolonization. Stochastic (chance) events contribute greatly to variability in the community. The major cause of variability is the supply of settling planktonic propagules of species in the community (Hawkins & Hartnoll 1982, Hartnoll & Hawkins 1985; Gaines & Roughgarden 1985; Gaines & Bertness 1992). Disturbance due to major climatic events such as storms and cold winters (e.g. Crisp 1964) or small-scale physical damage (Paine & Levin 1981; Shanks & Wright 1986) can have important effects.

No information available.

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