Rocky shores

Topographically, rocky shorelines are more variable than many other coastal habitats, depending heavily on local geology as to whether they are steep, overhanging, cliffs to wide, gradually sloping platforms, to severely dissected, irregular formations, and even large boulders. Characterising all these different shorelines is an open exposure to oceanic swells and extreme wave action, with the most notable exception being the sheltered coastlines of fjords such as occur in Norway and New Zealand. Water movement and desiccation have influenced the diversity of intertidal rocky shore species. A range of behavioural, physical and physiological adaptations determine an organisms resistance to desiccation during periods of exposure. Strong wave action has favoured the evolution of strong attachment devices such as algal holdfasts, cementation of barnacles, the byssus threads of mussels and the adhesive feet of gastropods and echinoderms. The use of crevices and formation of dense aggregations achieve a similar purpose.

The need to avoid being washed off the rocks means that most organisms on rocky shores are sessile or have limited motile ability. Competition for space is therefore intense and organisms inhabiting rocky shores occupy well defined zones. It also means that they can be particularly vulnerable to disturbances such as oil spills, especially if these occur during clam periods which extend the residence time of the pollutants. However rocky shores are generally exposed, high energy, environments and are less vulnerable than most to pollution. These features also limit other destructive human activities responsible for degrading other marine habitats such as construction.

Rocky shores provide a unique habitat for plant growth with a stable substrate for attachment, shallow well-light water turbulent and therefore rich in nutrients. Consequently macro-algae communities, dominated by kelps (Laminaria, Ecklonia, Macrocystis) and fuccoids (Fucus, Ascophyllum) flourish, mainly in temperate regions but also in areas of the tropics where seasonal upwellings of cold water occur, such as Chile and the southern Arabian coast. The net primary productivity of kelp forests is comparable to tropical rainforests and Macrocystis pyrifera, the giant kelp, is one of the fastest growing of all plants, up to 45 cm a day.