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).
Next - Section III. Invertebrate and Vertebrate Assemblages Associated with Kelp Forests
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