California’s Ocean Habitats: Kelp Forests

harbor seal
Bountiful food in the kelp forest attracts marine mammals like this harbor seal in Matlahuayl State Marine Reserve
CDFW photo by M. Haggerty

Kelp forests provide countless ecosystem services, benefiting both marine species and landlubbers alike. They form the foundation of marine food webs, coastal economies, and Indigenous traditions. They protect juvenile fish from predation by providing nursery habitat, and coastlines from erosion by buffering wave energy. Kelp forests help mitigate the effects of climate change and ocean acidification by storing enormous amounts of carbon, possibly even more per area than their terrestrial forest counterparts. The oxygen produced by kelp photosynthesis may even make its way into the air you breathe! 

beach wrack
Bull kelp washed ashore at Asilomar State Marine Reserve
CDFW photo by K. Gonzales

If you’ve been to one of California’s beaches after a big winter storm, you’ve probably seen (and smelled) the piles of seaweed washed up on shore. It is a rather dull end for some of California’s most iconic species – did you know that before getting stranded on land, those seaweeds, or kelp, anchored a complex underwater forest teeming with colorful sea life?

Though they look and act much like plants, the species of seaweeds that fall under the term kelp are actually brown algae. Superficially, their structure is very similar to that of plants. The kelp’s holdfast is comparable to the roots, anchoring it to the rocky ocean floor. From the stipe emerge the blades, just like leaves on a stem. Kelp takes up nutrients from the surrounding ocean waters through the stipe and blades, but not the holdfast. Many kelp species also have pneumatocysts, or air-filled sacs, that provide the buoyancy needed to grow towards the sunlight penetrating the ocean surface.

Like plants, kelp is a primary producer, meaning that it uses energy from the sun to make its own food through photosynthesis. To thrive, kelp needs plenty of sunlight, rocky ocean bottoms for attachment, and cold, clear, nutrient-rich waters. Wherever such suitable habitat exists, many kelp individuals may grow together in close proximity, creating a kelp forest, one of the ocean’s most diverse and productive ecosystems.

kelp forest
Sunlight beams through the kelp forest canopy at Scorpion State Marine Reserve
CDFW photo by A. Van Diggelen

Kelp forests are found off the coast of every continent except Antarctica. In California, kelp forests can be found in patches along the entire coastline, from close to shore to more than 100 feet deep. As many as 20 different species of kelp comprise California’s kelp forests, with each species contributing to the forest’s structural complexity. The canopy-forming kelps, bull kelp (Nereocystis luetkeana) and giant kelp (Macrocystis pyrifera), grow extremely quickly, sometimes eventually extending more than 100 feet tall; in fact, giant kelp is the largest marine alga in the world and can grow up to two feet per day!

Upon reaching the ocean surface, the blades of bull and giant kelp spread and entwine to form canopies up to ten feet thick. Beneath the canopy, other kelp species form layers of understory, just like the tiers formed by grasses, shrubs, and small trees in forests on land. In Southern California, this understory may contain the distinctive elk kelp (Pelagophycus porra). The winged or stalked kelp (Pterygophora californica) and the southern sea palm (Ecklonia arborea) create dense canopies up to eight feet above rocky reefs along parts of the coast. The flatter growth of Laminaria farlowii spreads across the rocky seafloor, overlaying seemingly endless forms of algae growing on the rocks. Bits of detached kelp drift to the ocean floor, just like the nutrient-rich layer of leaf litter on the forest floor.

Inhabitants of the Kelp Forest
All these forest layers create a number of places for other species to live, rest, hide, and eat. With hundreds of inhabitants, ranging in size from microscopic plankton to the great gray whale, the diversity of life in a kelp forest is tremendous. Life forms with no terrestrial counterpart, often brilliantly colored, make their homes on the ocean floor, creating an otherworldly landscape.

Kaleidoscopic nudibranchs and predatory sea stars patrol the seabed, searching for their favorite foods, like snails and sponges. Other animals wait for their food to come to them – sea anemones catch and immobilize passing prey like crabs and small fish in their stinging tentacles, while sea sponges create a current around themselves to filter tiny food particles out of the water. Cabezon, rockfish, lingcod, and leopard sharks are some of the fish species that stick close to the buffet on the ocean floor. Other benthic, or seafloor-dwelling, species are a bit harder to see, using various methods of camouflage to mask their presence. The highly intelligent red octopus can change not only its color, but also its texture to match its surroundings, while the innovative decorator crab evades detection by covering itself in bits of algae or even tiny animals.

Some animals live and feed on the kelp itself. Sea urchins are common on the ocean floor, dining on kelp. Various snails, such as the jeweled top snail and the blue top snail, lay claim to different heights of the stipe, and the blades of the kelp may be inhabited by colonies of bryozoans. Abalone are important grazers of unattached drift kelp. The garibaldi, California’s state marine fish, builds and defends nests on rocks among the kelp fronds. Many other types of fish can be found swimming among the blades of the kelp forest, including señoritas, sea bass, and perch. At the sea surface, playful sea otters wrap themselves in kelp to stay in place while they nap, and birds like gulls and cormorants are attracted to the abundant food found in the kelp forest. Even the kelp that washes on shore gets gobbled up by sand-dwelling critters.

garibaldi nest
Garibaldis guard their nest in Matlahuayl State Marine Reserve.
photo by S. Wertz

Marine mammals, such as harbor seals, sea lions, and gray whales, use kelp forests not only as feeding grounds but also as places to hide from their predators, like orcas. Each of these mighty mammals, when they die, become food for all sorts of scavengers and decomposers on the ocean floor. In this way, the food web keeps flowing and the kelp forest ecosystem remains in dynamic balance.

Humans have a variety of uses for kelp as well. For countless generations, Native American Tribes have collected kelp for uses that include a nutrient-rich source of food, a salt source, for medicinal use, and for making various tools. During World War I, potassium was extracted from kelp in processing plants along the California coast to make gunpowder. Throughout the twentieth century, the algin extracted from California’s kelp was used as a binding and gelling agent in a multitude of foods and medicines. Today, kelp is harvested in much smaller quantities, primarily to feed aquacultured abalone and to be dried and sold as human food. New uses for kelp, such as a source for renewable energy, are also being explored.

Of the more than 300 marine species harvested commercially in California, many of them spend at least part of their lives in kelp forests. Most ocean-based recreational activities, from bird watching to scuba diving, are enriched by the diversity and beauty of kelp forests. Even folks far removed from the ocean receive the benefits of kelp forests: as part of photosynthesis, kelp removes carbon dioxide, the primary greenhouse gas contributing to global warming, and releases the oxygen that sustains us and other animals.

Yet kelp forests are not indestructible. In ecology, resilience is the ability of an ecosystem to bounce back from a disturbance. From being displaced by seasonal storms to getting munched on by hungry sea creatures, kelp forests have evolved to withstand all kinds of things. However, humans have added novel disturbances to ocean habitats, such as pollution, sedimentation from urban development activities, and introductions of non-native invasive species, such as the invasive seaweeds Undaria pinnatifida and Sargassum horneri. Fishing has reduced the number of certain top predators and competitors in some kelp forests around the world, allowing the populations of kelp-eating herbivores like urchins to explode and devour entire kelp beds.

Climate change is further testing the resilience of these majestic ecosystems by increasing the frequency and severity of disturbances; for example, a ‘perfect storm’ of warm seawater, disease, and increased consumption of kelp by various species,  exacerbated by climate change, led to an over 90 percent decline in bull kelp along California’s Sonoma and Mendocino County coasts between 2014 and 2016. California Sea Grant, the California Department of Fish and Wildlife, and the California Ocean Protection Council, in collaboration with a variety of partners, including commercial and recreational resource users, academia, non-governmental organizations, Tribes, and federal agencies, have initiated several pilot restoration and research projects to evaluate methods of kelp recovery throughout the state. These projects include reducing urchin grazing pressure, determining the most effective methods to out-plant kelp to help it recover, and increased efforts to understand the conditions that drive kelp decline and recovery.

Kelp Forests in Marine Protected Areas

diver with banner
California’s network of MPAs protects about 16 percent of state waters and includes habitats like kelp forests.
CDFW photo by A. Van Diggelen

Another step taken towards kelp forest conservation was the creation of marine protected areas (MPAs) statewide. In 1999, California’s state legislature passed the Marine Life Protection Act aimed at, among other things, protecting and conserving the diversity of life and habitats that flourish in the state’s ocean waters. To achieve this, the Marine Life Protection Act directed the state to establish and maintain an ecologically connected network of MPAs. Over the subsequent 12 years and planning processes in four coastal regions, 124 MPAs were established, creating one of the largest science-based, stakeholder-driven MPA networks in the world.

MPAs are an effective way to protect habitats like kelp forests because they protect entire ecosystems holistically rather than individual species separately. With certain human pressures like fishing prohibited in some MPAs, the linkages between species remain relatively intact and habitats such as kelp forests may be buffered against other stresses and disturbances. As directed by the Marine Life Protection Act, scientists regularly study MPAs to assess long-term changes in the health of ecosystems like kelp forests and gather data that can inform adaptive management.

If you want to see kelp forests for yourself, you can visit them in a number of MPAs. You can (scuba or free) dive right in at MPAs statewide, from Casino Point State Marine Conservation Area (SMCA) or Kashtayit SMCA in Southern California, to Double Cone Rock SMCA in northern California. You can also cruise around in a kayak if you’d rather be on the water than in it. If you prefer to stay onshore, look for sea otters wrapped in kelp from the rocky headlands of Point Lobos State Marine Reserve (SMR) along the central California coast or for sea lions mingling in the kelp canopy from the rugged points jutting into Scorpion SMR. No matter where you are along California’s coast, there is usually a kelp forest waiting for you.

Besides visiting MPAs with kelp forests, here are some other things you can do to learn more and help protect these incredible ecosystems:

post by Kara Gonzales, CDFW Environmental Scientist