Kelp – Forests in the Sea

During an ideal day, few places on earth appear more inviting than a southern California kelp forest. On the surface, the Pacific is calm,...

During an ideal day, few places on earth appear more inviting than a southern California kelp forest. On the surface, the Pacific is calm, the water warm, and there is hardly a cloud in the sky. Underwater, shimmering rays of sunlight dance through towering forests of giant kelp as waves roll gently overhead. Golden hues of kelp fronds stand out in striking fashion against a background of blue-green water. In some kelp forests, crops of bright-green eelgrass flow with the surge along the sea floor.

At a depth of 10 to 20 feet/3 to 6 m below the surface, canopy divers become aware of the rhythmic sway of the forest as it keeps time with the ocean’s movements. As far as one can see, the entire forest moves gently back and forth with the surge, the plants and animals within moving in perfect synchronization with the ocean’s ebb and flow. It is a truly magical sight, one that can be said to be somewhat like swimming through a “Disneyesque” underwater redwood forest.

Liquid Forest

The forest analogy is a valid comparison for many reasons. Giant kelp plants typically grow in close proximity to one another, and because the towering “tree-like” plants often grow in large patches that cover up to 10 square miles/26 sq. km, the term forest seems apropos. Though stunning, it is not merely the foliage alone that divers find so alluring. More than 800 species of marine animals can be encountered in a healthy kelp forest ecosystem, and it is their presence that attracts so many divers. In a typical kelp forest, also known as a kelp bed, there are so many organisms using the resources of the ecosystem for food, habitat, protection and substrate for attachment that it is difficult to calculate the sheer numbers. By itself, a single fully mature plant can support more than one million marine organisms, and there can be thousands of plants in a given kelp bed. Of course, many of those organisms are microscopic, but there are plenty of others that can easily be observed with the naked eye.

It was Charles Darwin, the famous evolutionary biologist, who first noted the ecological importance of kelp forests when in 1834 he proclaimed:

“The number of living creatures of all orders whose existence intimately depends on kelp is wonderful. A great volume might be written describing the inhabitants of one of these beds of seaweed…. I can only compare these great aquatic forests…with terrestrial ones in the intertropical regions. Yet, if in any other country a forest was destroyed, I do not believe so many species of animals would perish as would here, from the destruction of kelp.”

The last sentence of Darwin’s statement is certainly suspect due to the recent discovery of so many species of insects and birds in tropical rain forests. Nevertheless, modern science continues to acknowledge the biological importance of the forests as first acclaimed by Darwin.

Giant Kelp

A variety of species of plants called kelp are found in many areas around the world, ranging from Canada to Argentina to New Zealand to California. There are at least 21 species found in California waters alone. Of these, several species are more prominent as far as recreational divers are concerned. Feather boa kelp, several species commonly known as palm kelp, elk kelp, laminaria and bull kelp are just a few, but it is the species commonly called giant kelp that dominates the waters of southern California.

While it is true that in many instances several of these species occur in the same area, there are significant differences in concentration in various geographical and oceanic zones. Clearly, because of its size, beauty, prominence and the fact that it dominates so many of southern California’s more highly publicized dive sites, the species known as giant kelp is the first and only species that many people think of when they think about diving in a kelp forest.

Scientifically known by its taxonomic name, Macrocystis pyrifera, giant kelp is the mainstay of the Southern California kelp forest ecosystem. Giant kelp is a brown seaweed, a type of algae that has descended from plants which survived the ice ages. Seaweeds are not as complex as flowering plants, lacking specialized tissues that carry water and food from one part of the plant to another. However, in many forms seaweeds have demonstrated a remarkable ability to survive in very demanding circumstances.

Giant kelp is a classic example. Expansive beds of giant kelp thrive in areas where there is too much water motion and current for many other plants to survive. However, the water flow provides a continuously renewed supply of nutrients, such as nitrogen, potassium and sodium, all of which are absorbed by the kelp and vital to the plants’ survival.

Giant kelp is both the fastest-growing and largest plant in any marine environment. When experiencing ideal growing conditions, a giant kelp plant can increase its length by as much as 2 feet/.6 m in a single day. In only six to eight months of good conditions, a kelp plant can reach the surface from a starting depth of up to 130 feet/40 m. This species rarely grows from any deeper, yet individual plants commonly reach lengths of up to 200 feet/61 m as the golden stipes grow straight up from the sea floor to the surface, where they stretch out horizontally to form a floating canopy. In a healthy forest during late summer and fall, the canopy can be up to 10 feet thick. Even on cloudless days the suspended overhang of a healthy canopy blocks and scatters some of the light from the sun, creating a stunning, cathedral-like effect for divers, who easily have room to maneuver below the canopy.

Healthy beds of Macrocystis, as giant kelp is sometimes called by experienced sport divers due to its genus name, are found only in regions where the water temperature stays between 50˚ and 68˚F/10˚ and 20˚C on a year-round basis. With very few exceptions, kelp beds occur in areas with rocky substrate. Forests of giant kelp occur in waters ranging from Santa Cruz, California, in the north to Turtle Bay, roughly halfway down the Pacific side of Mexico’s Baja peninsula in the south. Mature plants are comprised of a stemlike stipe, a number of leaflike appendages called blades, and gas bladders. The blades attach to the stipe via connective tissues called pedicels.


As is the case with all species of kelp, giant kelp plants have no true root system, but instead depend upon a system of short, thin, sturdy structures called haptera, which look like oversized pieces of golden spaghetti. Collectively, the numerous haptera form a structure known as a holdfast, which serves to attach the plant to the bottom.

The holdfasts do not penetrate the substrate as is the case with the roots of flowering plants. They are, however, well-designed both for gripping the sea floor and for resisting the constant shock and pull of wave action, surge and current. However, severe winter storms, a major threat to kelp forests, often rip holdfasts loose from their attachment points on the bottom. In the sea, kelp fronds float upward as gas bladders called pneumatocysts (new-mat-o-sists) buoy the plants.

The pneumatocysts are found between the stipe and blades. Their buoyancy allows the fronds to reach the surface where the plants receive sunlight, an ingredient vital to photosynthesis, the process through which plants convert sunlight to energy.

Unlike terrestrial plants, which take in most of their nourishment through their roots, kelp absorbs nutrients from the water through all of the plant’s surfaces. Kelp blades have no top or bottom side. This feature enables the blades to conduct photosynthesis on both sides rather than only on the top. The end result is that kelp can grow very rapidly even though the blades are constantly being flipped over by water action. In fact, the entire frond takes part in photosynthesis.

Out of the water, kelp is quite heavy, and large, entangled clumps often litter Southern California beaches, especially after heavy winter storms. However, in 1997 and early 1998, despite intense El Niño-driven storms, there wasn’t much kelp piled up on area beaches. The reason is that the extremely warm water that preceded the winter storms for several months caused the near disappearance of kelp forests throughout the region prior to the onset of winter. However, many scientists believe there is little cause for long-term concern, as they fully expect Southern California’s giant kelp forests to rebound as the water cools and the storms lessen in frequency and intensity.

On rough and stormy days, shadow-filled kelp forests often appear dark and ominous. When the sea is churning, the towering plants constantly tug at their holdfasts, often pulling free from the bottom and becoming entangled with other plants, which in turn pull free and entangle neighboring plants in a destructive domino effect.


Giant kelp forests provide a wonderful opportunity to observe a diversity of marine creatures in a setting that is accurately described with overused terms such as awesome, magnificent, breathtaking and stunning. Bright-orange garibaldi, a damselfish that is California’s state marine fish; flowing schools of silver jack mackerel; hovering schools of blacksmith fish; señorita fish; halfmoon, a variety of perches; curious sheephead; and rockfish are abundant in many kelp forests. So are ling cod, cabezon, sculpin, moray eels and cleaner shrimp, blue-banded and black-eyed gobies, blennies, convictfish and many more species of fishes. Occasional visitors include migratory fishes such as yellowtail and barracuda. Once heavily pursued by sport fishermen, spearfishermen and commercial fishermen, the largest of kelp forest fishes, the black seabass, is making a wonderful comeback. It is no longer uncommon for divers to look up and discover a 300-pound/136-kg black seabass staring back at them. It is the sort of diving moment that makes life move in “slow motion.”

California spiny lobster, abalone and a host of dazzling invertebrates ranging from corynactus, aggregate and Urticina (ur-ti-seen-a) anemones (formerly known as Tealia anemones) to sea stars to rainbow-colored nudibranchs to octopi tosea fans and purple coral await on many reefs. All of these are common sights. And you just never know when you will be lucky enough to swim with a herd of playful California sea lions or a harbor seal. You might look up through the kelp as a 40-foot-/12-m-long, 80,000-pound/36,000-kg California gray whale cruises silently overhead. It happens!

Even during more ordinary dives, you can’t help but marvel at life in a kelp forest community. More than 178 species live in the holdfasts alone. This list includes creatures such as crabs, nudibranchs, brittle stars, isopods and worms. Scientists have documented more than 100 species of motile invertebrates that commonly associate with giant kelp fronds. These species include a wonderful sampling of shrimps, crabs and snails that provide divers with plenty of entertainment. While many of the smaller creatures of mysid shrimps, amphipods, copepods, isopods, bryozoans and hydroids tend to go unnoticed by sport divers, their presence does help to attract more than 125 species of fishes commonly seen in kelp communities.

One of the more colorful snails is an animal commonly called a kelp snail (Norrisa norrisi). This 2- to 3-inch/5- to 8-cm-long snail, which can be identified by its golden shell and bright-red foot, lives its entire life while browsing on the kelp, traveling from the holdfast to the blades as it feeds. A variety of colorful anemones, crabs and shrimp can often be found on the fronds. And a magical master of camouflage known as a giant kelp fish can simultaneously delight and frustrate you. These fish are difficult to find and easy to lose sight of, because they are well-designed to look like invertebrate-encrusted blades of kelp, and mimic their movements as they flow back and forth with surge. But once you “lock on” visually, these gorgeous fish are wonderful sights to behold. Giant kelp fish reach a length of 24 inches/62 cm.

Life Cycle

Of fundamental importance to the overall health of a kelp ecosystem is the fact that while individual kelp plants often live for several years, the blades have a life span of only a few months. When they die, the blades fall off and decay. The dead kelp is known as shed, or kelp shed. The relatively short life span of the blades prevents colonies of encrusting animals such as bryozoans and hydroids from overweighting kelp plants and causing them to sink. Kelp depends on sunlight, and sinking would prevent the plants from gaining access to this vital resource at the surface. Equally important, the constant natural process of growth, dying and decaying provides the primary source of food for many animals such as sea cucumbers, urchin, sea stars and more in kelp communities.

Grazers and Feeders

Two principal food chains are directly associated with giant kelp. They are the chain of grazers, sometimes called browsers, and the chain of detritus feeders.

Grazers such as kelp snails, abalone, crustaceans and fishes feed on parts of living kelp plants. Detritus feeders like sea cucumbers, bat stars and lobsters feed on nutrient-rich decaying shed. Some animals, such as sea urchins, eagerly feed on the living plant and the shed. They are considered to be both grazers and detritus feeders. Of course, as you investigate further up many food chains, you will discover a multitude of species that are drawn to the forests to prey upon the grazers and detritus feeders.

As with all species of kelp, giant kelp reproduces through a procedure known as alternation of generations, in which a sexually reproducing generation alternates with an asexually reproducing generation. Thus, the complete reproductive cycle consists of two generations of plants.


Over the years man’s impact on the kelp forests has placed many beds in great jeopardy. During the 1800s and early 1900s men, both hunters and trappers, intensely overpursued the highly valued pelts of sea otters, hunting those mammals to the point of near extinction. Sea otters prey upon sea urchins, helping to maintain normal population sizes in healthy forest ecosystems. Thus, with the demise of sea otter populations came a corresponding increase in the number of sea urchins.

The unchecked expansion of sea urchins created intense competition for food among the urchins. While urchins normally prefer to feed on kelp shed, when competition for food increases, urchins will readily forage on kelp holdfasts. When their holdfasts are weakened, kelp plants often get pulled free from the sea floor and perish. Once adrift, a given kelp plant frequently becomes entangled with other plants, tearing them away as well. This chain of events severely threatened the very existence of a great many kelp forests.

In 1913 sea otters in California waters became protected by law, and by the 1950s and 1960s were numerous enough to again control sea urchin populations in many areas. During the same time period, conservationists began planting healthy kelp in deteriorating forests to supplement natural regrowth of kelp. In some endangered kelp beds where natural predators of sea urchins were rare, quicklime (calcium oxide) was utilized to decrease the numbers of grazing sea urchins. Owing at least in part to these efforts, many kelp forests made strong comebacks.

With few exceptions, holdfasts are generally incapable of attaching to sand, mud or even silt-covered rocks. This fact helps explain the dramatic demise of numerous kelp forests located near the sewage outfalls of major metropolitan areas along the Southern California coast during the 1950s, ’60s and early ’70s. The sewage created a layer of silt over the bottom, preventing new holdfasts from attaching, and as a result, thousands of square miles of kelp beds perished. In addition, high concentrations of phosphates and other chemicals in the sewage killed many existing plants and decreased water clarity, limiting the amount of light available to the kelp for photosynthesis and threatening the kelp’s ability to survive.

Furthermore, as waste settles it can bury and kill tiny young kelp plants before they have a chance to establish themselves. The layer of silt sometimes makes it difficult for new haptera to gain a grip on the substrate, making it even easier for tiny holdfasts to be torn from the sea floor. In recent years Californians have become much more aware of the significant impact caused by sewage, and many communities have taken responsible action to prevent similar reoccurrences.

If anything positive is to be gained from this chain of events, it is an understanding of the vulnerability of the kelp forest habitat. Although they appear quite rugged, kelp forests can be quickly destroyed by overexploitation of the kelp or of many other vital members of the kelp community. Loss of the kelp forests would not only be a tragic waste of a beautiful habitat, it would deprive California of uncountable revenue. If exploited without proper concern, kelp forests can be destroyed in very little time. On the other hand, if we protect this valuable ecosystem, California kelp forests can continue to provide economic resources, as well as home, food and shelter for many marine species, for years to come.

Swimming, Snorkeling and Diving

In Hollywood lore, kelp is often considered to be a man-eating monster, having the ability to reach out and entangle any swimmer or diver who as much as blinks while swimming through a kelp forest. With just a little common sense you can generally avoid even the slightest entanglement, but even if you do get caught in some kelp, it is quite easy to get free.

Kelp is highly elastic, but it can also be broken easily. If you do happen to become slightly entangled, or if a fin buckle, console or tank valve gets hung up in a stipe, simply snap it in half in much the same way you might break a pencil. You may need to bend it back and forth a few times before it snaps. If you do somehow manage to get really tangled in the stuff, a knife can help.

Monitor your air supply so you can avoid having to pick your way over and through a thick surface canopy of kelp. Using your compass and paying attention to where you are can help you avoid unwanted surface swims.

Plan your dive so that you ascend and descend at the edge of a kelp bed. Streamline your gear and secure gauges and hoses so you can avoid potential entanglements. Finally, consider enrolling in a kelp diving specialty course.

Kelp as a Valuable Commercial Resource

Beyond the purely esoteric value of its beauty, giant kelp has many other uses. In 1911 the United States Department of Agriculture sponsored a study of the kelp beds, and since that time numerous industrial uses for kelp have been developed. During World War I kelp was harvested and processed into potash and acetone for use in the munitions industry.

Shortly afterwards, researchers discovered that algin, a colloidal substance found in kelp, has many commercial applications. Available only from certain sea plants, algin has a strong affinity for water. It is therefore extremely useful as a suspending, stabilizing, emulsifying, gel-producing and film-forming additive. Algin is used in hundreds of commercial and household products, including ice cream, beer, fruit drinks, egg nog, candy, cake mixes, paint, paper sizing, medications, toothpaste and hand lotions.

In 1996 researchers at NutraSweet® Kelco Co. (a unit of Monsanto), the largest commercial harvester of kelp on the west coast, began development of an innovative new use for algin. Scientists are now able to purify algin to such an extent as to eliminate all trace compounds detectable by the human body’s immune system. Although further research is required, the potential for biomedical applications is tremendously exciting!

For instance, it may be possible to reduce rejections of donated and artificial organs by coating them with ultra-pure algin prior to transplantation. Since current research indicates that the recipient’s immune system should not recognize the ultra-pure algin as a foreign substance, the new organ may be much more readily accepted. If ongoing studies and tests continue to be promising, this is only one among countless examples of future potential uses of ultra-pure algin in saving and improving human lives.

Commercial harvesting of kelp is regulated by the California Department of Fish and Game. Modern techniques employ the use of ships that work much like wheat combines, cutting through the top 3 or 4 feet/1 m of the surface canopy. The strands of kelp are then collected on large conveyor belts and taken to industrial plants for processing. Kelp-related industries provide jobs for many California residents. In fact, recent estimates indicate that commercial harvesting of kelp generates well over $100 million annually for southern California’s economy.

Story and photos by Marty Snyderman