Both microalgae and macroalgae are abundant and diverse on the outer coast. Over 120 species of algae have been identified in the rocky intertidal areas of the outer coast of the Olympic National Park (Dethier, 1988). Microalgae are primarily composed of benthic diatoms which are found as thin coatings on rocks or living within the sediment. These diatoms are an important part of the "algal film" forming diatom slicks on rocks and providing a principal food source for many grazing animals such as gastropods and chitons (McConnaughey, 1970). Marine lichens are found as thin veneers on rocks in the highest intertidal areas on exposed rocky areas.

Macroalgae are seaweed that grow attached to a firm substrate from the intertidal region down to as deep as 40m. The seaweeds are composed of three main phyla: red algae (Rhodophyta), brown algae (Phaeophyta), and green algae (Chlorophyta). Kendrick and Moorhead (1987) present a summary of the algal species found, or expected to occur, at three intertidal sites along the coast of the Olympic National Park. The authors also discuss using two species of algae (Fucus distichus, and Endocladia muricata) as potential indicators of recreational impact on the intertidal communities of the National Park.

The red algae are the most diverse of the macroalgae in terms of number of genera (about 115) and species (at least 265) in the Pacific Northwest (Waaland, 1977). In intertidal and shallow subtidal areas, red algae often occupy the understory of the larger kelps.

Less common in the exposed areas of the outer coast, green algae inhabit the more protected marine and estuarine areas in Washington. These algae reside primarily in tidepools and rocky intertidal areas.

Brown algae include the largest marine plants and are probably the most important macroalgal group in terms of primary productivity and direct economic value (Gardner, 1981). Brown algae vary from the large kelps to the less conspicuous forms that encrust rocks or form filaments on other algae. The Pacific Northwest coast supports the highest diversity of kelps in the world (Dayton, 1985). Two species of brown algae dominate the extensive kelp forests of the outer coast: the bull kelp (Nereocystis leutkeana) which is found in relatively protected waters; and the giant kelp (Macrocystis intergrifolia) which prefers more exposed areas (Steelquist, 1987). Macrocystis beds extend into the Strait of Juan de Fuca to Crescent Rock. Some of the most proliferous macrocystis beds in the state are found in the Strait.

Algae play an important role in the functioning of the entire coastal ecosystem. Beside being a direct food source for animals, algae (especially kelps) produce large amounts of dead plant material (detritus) which is the basis for the detrital food web. Duggins et al. (1989) showed that growth rates of benthic suspension feeders are two to five times as high at kelp-dominated islands as at those without kelp beds. Algae provide important habitat for many animals and function as nursery and spawning areas for small fish. Sea otters and many species of fish closely associate with giant kelp forests.

Seaweed
Species List