Channel Islands National Marine Sanctuary is home to one-third of southern California’s kelp forests (Davies, 1968). Giant kelp (Macrocystis pyrifera) is the primary species in the region and forms extensive underwater beds on rocky substrates at depths between 10 and 100 ft. This particular species of kelp ranges from Año Nuevo to Baja California and down to South America. These impressive, underwater forests are conspicuous features of the sanctuary and important not only to the regional ecology, but to recreational and commercial interests as well.
Kelp has a root-like structure called a holdfast that adheres to hard substrate, thereby anchor the growing alga. There are special reproductive blades (sporophylls) near the holdfast that produce spores. Many slender stipes are buoyed towards the surface with gas filled bulbs at the base of broad, wrinkled blades. When the kelp reaches the surface it spreads out creating a thick canopy. Individual kelp fronds live only about 6 months, but new fronds are continually produced during the multi-year life span of the plant (Rosenthal et al. 1974). During this time giant kelp fronds can grow between 10 in and 2 ft per day.
Kelp beds in the sanctuary are productive habitats that provide food, habitat, and shelter for a myriad of invertebrates, fishes, marine mammals and seabirds. The dense thicket of giant kelp in the water column and at the surface is particularly important as a nursery habitat for juvenile fishes (Carr 1989). Kelp forests are important locations for recreational scuba diving, wildlife viewing, kayaking and fishing. Historically, giant kelp has been harvested for commercial purposes throughout California, however this is prohibited within CINMS boundaries.
Locations supporting giant kelp generally have been consistent through time, but the extent of these beds has varied considerably based on environmental conditions and human impact. Overall, kelp forests have declined over time throughout southern California including at the Channel Islands. Kelp abundance is affected by natural forces such as storms, water temperature and wave action, but it is the human impact that has had the biggest influence. In addition to natural changes, the historic overharvesting of predators such as sea otters, spiny lobsters and California sheephead has resulted in an overabundance of herbivorous invertebrates, which in turn has led to the overgrazing of kelp forests.
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