The general patterns of zonation on rocky shores can be explained in terms of physical factors affecting the outcome of biological interactions. The diversity of species on rocky shores increases towards the lower shore where conditions are damper. 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 that 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. The level of larval supply and its fluctuation plays 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). Dissolved organic carbon, algal fragments and microbial film organisms are continually removed by the sea. This may 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 biochemicals to pelagic food chains.

Pelvetia canaliculata, Fucus spiralis, Fucus vesiculosus, Ascophyllum nodosum, Fucus serratus

Fish and crustaceans migrating into the intertidal to feed as the tide rises, are important predators of rocky shore species. Juveniles are commonly found in rockpools. Shore birds also feed on the rocky shore (Feare & Summers 1985). The invertebrates attracted to seaweed on the strandline are a particularly important food source. Rich pickings can also be had under macroalgae canopies. Otters Lutra lutra often use rocky shores and will feed on animals such as shore crabs Carcinus maenas which, in turn feed on rocky shore species.

Rocky shore communities are often highly variable in time, due to the combined effects of physical disturbance, competition, grazing, predation and variation in recruitment. However sheltered shores tend to be less variable than exposed or moderately exposed shores and are therefore more stable.

No information available.

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