Vertebrates tend to be transient species that use the intertidal zone to feed or hide and include fish and marine mammals that enter at high tide and birds and terrestrial mammals that enter at low tide (Figure 3). For instance, marine iguanas (Amblyrhynchus cristatus) of the Galapagos Islands, Ecuador forage extensively on intertidal algae on lava reefs during low tides. The major exceptions are resident intertidal fishes, which are often cryptic and less than 10 cm in length. Resident and transient fishes include hundreds of species from dozens of families, though members of the families Blenniidae, Gobiidae, and Labridae are the most common.
Birds and mammals, characterized by high endother-mic metabolic rates and large body sizes, have significant impacts on intertidal communities even at low densities. Birds include locally nesting and migratory species and can remove millions of invertebrates during a season. In addition, birds in some communities provide major inputs of nutrients via guano and prey remains. More than two dozen terrestrial mammals, mostly carnivores, rodents, and artiodactyls, have been reported as consumers or scavengers of rocky intertidal organisms on every continent except Antarctica. Most recorded prey species are mollusks, crabs, or fish. Probably one of the most unusual cases is a population of feral rabbits on a small island off the coast of South Africa that forage on seaweeds in the intertidal zone. Given the mobility of vertebrates, their impact on rocky intertidal shores has been difficult to assess and intertidal activity is often discovered by finding
Figure 3 Rocky shore in Central California, USA with elephant seals on the beach. Photo by S. Dudgeon.
exclusively intertidal animals or algae in the gut contents of otherwise pelagic or terrestrial species.
Little is known about the effects of harvesting by humans in the rocky intertidal zone. Results from a few large-scale studies in Australia, Chile, and South Africa, however, have demonstrated that harvesting has had significant effects on intertidal assemblages.
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