Lesson #2: The Rocky Shore Community

Although it's one of the most restricted habitats, the rocky intertidal region is one of the best known and studied of all habitats. It is well populated with marine organisms, some which may live in the subtidal zone, and others that are found living no where else. The members of this community have adapted to life in a habitat that experiences periodic air exposure, with all its associated problems, and the rigors of wave shock.

The rocky intertidal community abounds with plants and animals. They occur here in a diversity and abundance that rivals that of the adjoining subtidal community. Competition for living space is keen and no rock surface stays uncolonized for long. Plants and animals often live upon another, creating a multilayering of organisms at the mid- and low tide levels. At low tide this rich community becomes a feast for birds and land dwelling predators. At high tide it becomes the dinner table for a variety of fish. Coastal Indians made use of this resource and many people today take advantage of low tides to forage for abalone, mussels, crabs, kelp and much more.

Rocky Shore Habitats

Compared to other intertidal habitats, rocky shores tend to have a greater number of species of intertidal organisms. This increased diversity is the result of the greater variety of different habitats available for organisms to occupy. One can describe any number of habitats within a rocky shore system: for example boulder habitats, cobble habitats, rock/mud habitats, tide pool habitats, etc. The resulting diversity of species is locally further enhanced around headlands by the influence of the upwelling of cold, nutrient-rich offshore waters.

With the exception of boring clams, most rocky shore organisms live on the surface of rocks. The quality of the rock formation thus directly influences the types and numbers of organisms that can inhabit it. Shorelines composed of hard smooth rocks tend to have fewer kinds of animals than those of softer, more porous rock do. This is because hard smooth rocks have fewer cracks, holes, and depressions which animals can use as home sites. In addition, the surface of smooth dark rocks become much warmer during daytime exposures during low tide than that of lighter colored more porous rock. The stability of the rocky shore also influences the types and numbers of organisms that inhabit it. Shores composed of very large boulders are physically more stable than shores composed of smaller rocks, loose stones, or cobble. These areas of low stability are rearranged during each period of heavy wave action and very few species of animals can survive being tossed about and ground between rocks.

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