Research and Monitoring

      

Kelp Forest and Rocky Subtital Habitats
II. Algal Assemblages Associated with Kelp Forests

Within the MBNMS, there are rich algal assemblages associated with the kelp forests. Subsurface canopies of the stipitate kelps Pterygophora californica, Eisenia arborea, and several species of Laminaria occur beneath the surface canopies (McLean 1962, Foster and Schiel 1985, Harrold et al. 1988). Although they occur throughout the MBNMS, these understory kelps are more characteristic of exposed areas (Harrold et al. 1988). Other algae, such as fleshy red species, can form dense algal turfs under the canopies (Table 1; Breda and Foster 1985, Harrold et al. 1988) and are often distributed along a depth gradient (Harrold et al. 1988) with the more robust species occurring shallower and the more delicate species occurring deeper (McLean 1962, Devinny and Kirkwood 1974).

Kelp canopies alone or in combination with one another can reduce the amount of light reaching the substrate to less than 1% of surface irradiance (McLean 1962, Reed and Foster 1984). During the winter months along the central California coast, increased water motion from winter storms removes kelp canopies thereby increasing the amount of light reaching the substrate, which in turn can have dramatic effects on the algal assemblages beneath them (Foster 1982, Reed and Foster 1984, Breda and Foster 1985). One common phenomenon occurring in areas where surface canopies have been removed is the recruitment of the brown alga Desmarestia ligulata (Foster 1982, Reed and Foster 1984). This species forms a dense subsurface canopy which can inhibit recruitment of other algal species including giant kelp (Dayton et al. 1992).

Nongeniculate or encrusting coralline algae e.g., Lithothamnium spp. and Lithophyllum spp. and upright articulated or geniculate coralline algae e.g., Bossiella spp and Calliarthron spp. occur throughout the kelp forests and are generally more tolerant of increased water motion and thus abundant in exposed sites (Harrold et al. 1988). They also are apparently tolerant of low light and can dominate the substrate under multiple kelp canopies. In exposed areas like those at Point Santa Cruz, water motion and sand abrasion associated with storms cause an overall decrease in fleshy red algae in the winter, which then increases in the summer. This leads to an overall increase in species diversity as compared to more protected sites like those at Hopkins Marine Station in Monterey Bay (Breda and Foster 1985).

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