Kelp Forests: CINMS

Overview

Macroalgae and Marine Plants
Macroalgae (i.e., seaweed) and marine plants (i.e., seagrasses) are habitat-forming primary producers that grow in intertidal and shallow subtidal waters, generally less than 30 meters deep, where enough light penetrates for photosynthesis. The islands support a rich array of benthic algae and seagrasses. In southern California, there are at least 492 species of algae and four species of seagrasses known to occur from among the 673 total species described for California (Abbott and Hollensberg 1976, Murray and Bray 1993). These algae and marine plants are critical to the life history of many of the invertebrates, fishes, seabirds, and marine mammals found in the sanctuary. For example, giant kelp forms extensive underwater forests on rocky substrates at shallow subtidal depths. These impressive kelp forests are characteristic features of southern California nearshore marine environments, and are important not only ecologically, but also for recreational and commercial activities including fishing, diving, and tourism. Kelp beds are highly productive habitats and serve as important nursery habitat for juvenile fishes in the upper canopy (Carr 1994). They also provide food, attachment sites, and shelter for a diverse assemblage of invertebrates and other species of algae on the benthos, throughout the water column, and in the rootlike structure called the holdfast (Dayton 1985, Graham 2004). There are two types of marine flowering plants found in the sanctuary. Surf grass (Phyllospadix spp.) is found in rocky intertidal and shallow subtidal areas. Eelgrass (Zostera marina) is found in soft bottom subtidal areas. These plants form productive and complex habitats that provide food and refuge for a wide variety of marine species, including recreational and commercially important fish and invertebrates (den Hartog 1970, Orth et al. 1984, Hemminga and Duarte 2000). Seagrass beds provide nursery habitat (reviewed in Heck et al. 2003) and are important for nutrient cycling (Costanza et al. 1997) and substrate stabilization (Fonseca and Fisher 1986). Recent efforts have focused on restoring eelgrass beds at Anacapa Island. Eelgrass beds are also found at Santa Cruz and Santa Rosa islands.

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.

Giant kelp (Macrocystis pyrifera) off of Anacapa Island. Photo: Robert Schwemmer.
Giant kelp (Macrocystis pyrifera) off of Anacapa Island. Photo: Robert Schwemmer.

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.

OLYMPUS DIGITAL CAMERA
Giant kelp (Macrocystis pyrifera). Photo: Claire Fackler.

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.

Photos

Maps

Projects

Links