Giant Bladder Kelp
(Macrocystis pyrifera)


Giant kelp (Macrocystis pyrifera) is a species of marine alga found along the Pacific coast of North America from central California to Baja California. Although it begins life as a microscopic spore at the ocean floor, this species may grow to lengths of 60 m (200 ft) with its upper fronds forming a dense canopy at the surface. Giant kelp prefers depths less than 40 m (120 ft), temperatures less than 20ø C (72ø F), hard substrate such as rocky bottoms, and bottom light intensities above 1% that of the surface.

The genus name Macrocystis means "large bladder" and it contains at least two recognized species. Macrocystis pyrifera, or giant bladder kelp, is sometimes referred to as the sequoia of the sea. Macrocystis integrifolia is the small perennial kelp.

Geographic Distribution

In the Northern hemisphere it occurs only along the Pacific coasts of Canada, the United States and Baja California. Populations of Macrocystis in the North Pacific extend from Alaska to localities of cool, upwelled water in Baja California. The kelp beds along the Pacific coast are the most extensive and elaborate submarine forests in the world. The genus is best developed as the species Macrocystis pyrifera from the southern California Channel Islands to northwestern Baja California.

Kelp forestTemperate rain forest
© 2000 Dr. Mark Carr and Dr. Bill Bushing

Kelp Forests and Associated Species

There are five species of large brown kelps that may form canopies: Macrocystis or giant bladder kelp, Nereocystis or bull kelp, Pelagophycus or elk horn kelp, Egregia or feather boa kelp and Cystoseira which is a form of sargassum. South of Point Conception Egregia dominates the inshore waters and Macrocystis the intermediate depths with Pelagophycus offshore south of Point La Jolla.

The term kelp forest refers to the dense growths of Nereocystis, Macrocystis and Pelagophycus while the term kelp "beds" is used to refer to the smaller laminariales or brown algae which have limited vertical structure and canopies. A giant kelp forest may vary from several hundred feet to one mile wide and several miles long.

Macrocystis plays an important role in the marine environment by providing food and habitat for a wide range of marine invertebrates and fishes in southern California. Forests of giant kelp may support millions of individual organisms and more than 1,000 species of marine plants and animals.

The presence or absence of Macrocystis is not essential for the spawning of any sport fish species. However, kelp beds do provide shelter for the larvae and juveniles of several species such as the kelp topsmelt. The abundance and diversity of life associated with the structurally complex and high productive Macrocystis kelp populations are obvious. The giant kelp holdfast alone may contain over 150 species. Another report states 178 species were found living in the kelp holdfasts. 114 species of invertebrates were associated with the Macrocystis fronds in one study.

Factors Affecting Kelp

Macrocystis pyrifera usually does not occur shallower than about 5 meters or deeper than about 20 meters. From the holdfast to the tip of the longest frond these plants may reach lengths of 200 feet with 100 feet growing from the holdfast to the surface and another 100 feet stretched out in the canopy. Macrocystis is a perennial kelp with the holdfast surviving 4 to 10 years and the individual fronds 6 to 12 months.

Cartoon from the Tours de Jours comic strip that formerly appeared in
The Catalina Islander provided by Thelma Nowlin

© Bob Kingett

Giant kelp prefers areas with ocean temperatures above 5 degrees C (the lethal temperature for the gametophytes) and below 20 degrees C. The upper temperature limit may actually be a result of decreased nutrients, especially nitrogen, noted in warmer waters.

Nutrient levels are low in the summer and fall in southern California, especially above the thermocline and during periods when warm water masses move into the region from the south. The reduced summer growth of Macrocystis may be due to nitrate depletion. In southern California the giant kelp canopies commonly deteriorate during the summer when inorganic nitrogen is low.

Macrocystis and the other large algae are inhabited by a diverse range of pathogenic parasites, bacteria and fungi. Kelp plants may be found with tumors and galls, although few of these have been observed to cause severe damage to individual kelp plants. High water temperatures are often associated with a condition known as "black rot," which can result in considerable kelp mortality.

Kelp Growth and Life Cycle

Kelp begins life as a microscopic spore which grows into a tiny male or female plant called a gametophyte. These plants produce eggs and sperm, which fertilize and grow to form the large plants (sporophytes) we see along the coast here. The large sporophytes then release many new spores to start the process over again. The minimum amount of time needed to complete the Macrocystis life cycle is believed to be 12 to 14 months although in the environment, grazing by animals and shading by other plants would affect this rate of development.

Microscopic kelp gametophyte
© 2000 Dr. Ray Lewis

The average kelp plant is capable of releasing trillions of spores a year. Few, if any, of the billions of spores produced by a single mature Macrocystis kelp plant ever make it to adult gametophytes due to burial by sand or mud (sedimentation), comptetion for limited space with other plant or animal species, the lack of light at the ocean floor due to absorption by the water or shading by kelp and other plant species, nutrient limitation, and the effects of animals which graze on the tiny plants. Only 1 in 100,000 young kelp plants need to mature to reestablish the kelp beds. As the fertilized eggs develop into microscopic sporophytes, they must avoid shading and overgrowth by other organisms; grazing by small echinoids, gastropods, micro-crustacea and the bat star (Patiria); as well as being buried and abraded by sediments.

Microscopic kelp sporophyte plant
© 2000 Dr. Dan Reed

Microscopic kelp sporophyte plant
© 2000 Dr. Dan Reed

Studies suggest kelp fronds may grow at rates of 1-2 feet per day. Researchers at the Scripps Institution of Oceanography have measured Macrocystis kelp fronds elongating at 60 cm (2 feet) per day. Although giant kelp plants are perennial, the individual fronds only survive for about 6-9 months. Fronds of mature kelp plants become senile and deteriorate about 6 months after they are produced. Mature fronds continually develop, then die and break away in a process known as sloughing, giving way to the new fronds shooting up from the holdfast. Although the individual fronds only survive for about 6 months, individual blades last only about 4 months.

Young Macrocystis sporophyte plant
© 2000 Dr. Dan Reed

Harvesting of Kelp

Giant bladder kelp or Macrocystis is the easiest to harvest for several reasons. The fact that it is found in deep water habitat allows large harvesting boats to operate more easily. The surface canopy can be harvested several times a year without disturbing the submerged vegetative and reproductive parts which are located below the harvesting levels thus ensuring the kelp will continue to reproduce and the surface canopy will be regenerated by the younger fronds growing below the surface.

Nearly 400,000 wet tons per year were harvested during 1917 and 1918 as a source of potash. Some sources say that the potash was used for making gunpowder during World War I when German sources were unavailable. Other sources state that the potash from the California kelp forests was used commercially during World War I for fertilizer. In the early 1930's the algin-extraction industry was developed. The period from 1911 to 1919 was a time of feverish harvesting activity in California, induced by the high cost of potash during the years leading up to and during World War I. Many companies operated from San Diego to Santa Barbara extracting potash and acetone from kelp for the production of explosives. You could say we won the war with kelp.

After the War there was almost no harvesting of Macrocystis kelp from 1919 through the late 1920's. The emphasis later shifted from potash to algin production. The real rebirth of the California kelp industry in the late 1920's was the result of a discovery by E. C. C. Stanford in 1883. Kelp is the principle source of algin, a highly efficient thickening, stabilizing, suspending and gelling agent.

The harvesting of kelp in the state is regulated by the California Department of Fish and Game with the maintenance and improvement of the kelp beds important considerations. The State of California has imposed a number of restrictions on harvesting activities. Kelp harvesters are permitted to cut only the upper 1.2 meters (4 feet) of the water column. This regulation is to limit damage to the kelp's reproductive structures and allows vegetative regrowth from the unharvested fronds below the surface on cut plants. The kelp cutters cut the canopy in a strip 8 meters wide. Stands of kelp throughout the state are designated by number and some are leased by harvesting companies while others remain open to anyone with a harvesting permit. The kelp beds are leased for a period of 20 years. No more than 25 square miles or 50% of the total kelp bed area, whichever is greater, can be exclusively leased by one company.

Kelp harvesting vessel operated by Kelco, Inc.
© 2000 Dr. Ray Lewis

Today harvesting is done with boats that push "hedgeclipper knives that cut a 20 foot wide swath. The mowing method was developed around 1916. It used reciprocating blades mounted at the base of a conveyor system, cutting the kelp at a depth of about 1 meter as a barge was pushed through the kelp bed by a boat. Kelp harvesting is carried out mechanically by ships with mowing devices that cut only the top few feet of the kelp canopy. Small propellers push the harvesting vessel stern first through the water. The cut kelp is gathered on a conveyor system referred to as the drapers that is mounted on the stern and carries the kelp aboard. The actual processing of the kelp occurs on shore in San Diego. Modern harvesters carry as much as 550 metric tons of Macrocystis which can be collected in a single day of harvesting. Kelp harvesters are unable to work in depths less than 25 feet.

Kelp stipes that have been harvested will not grow back, but will live for a while and new stipes growing from the holdfast will replace them. People often think kelp harvesting is responsible for the seaweed litter on southern California beaches. 11 years of research by Dr. Claude ZoBell of the Scripps Institution of Oceanography answered this question. Harvested kelp amounted to less than 1% of the total litter appearing on beaches.

Detached kelp plants on the beach at
Little Harbor, Santa Catalina Island

© 2000 Dr. Bill Bushing

The kelp plants pictured above were torn loose in a storm and deposited on the beach at Little Harbor on Santa Catalina Island. These decaying kelp plants provide food for many of the sandy beach invertebrates including kelp flies and beach hoppers on the surface, and marine life that burrows into the sand (photo credit: Bill Bushing).

Kelco is based in San Diego with research, manufacturing and administrative facilities there as well as a research laboratory in Tadworth, England, and manufacturing plants in Oklahoma, England and Scotland. Kelco began operating as Kelco Company in 1929 and was acquired by Merck & Co., Inc. of Rahway, New Jersey, in 1972.

Commercial Uses of Kelp

Giant kelp has been used for years as a food supplement for many years because it contains iodine, potassium, other minerals, vitamins and carbohydrates. Algin is used as an emulsifier to bind oily and watery fluids together and is used for this purpose to prevent salad dressings from separating in containers. It is also a suspender to keep pigment particles mixed with the carrier as in paints, cosmetics and pharmaceuticals. Algin aids in controlling viscosity and makes ice cream smoother and cake icings stiffer. It is used to smooth and thicken more than 300 preparations from ice cream to paints, sauces and toothpaste.

Algin is used in a wide range of foods including desserts, gels, milkshake mixes, dairy products, canned foods, salad dressings, cake mixes, and meringues. Algin's hydrophilic, colloidal properties are also useful in the manufacture of food, drugs, cosmetics and building materials. Kelp products are also used in the manufacture of livestock and poultry feed, pharmaceuticals and fertilizers. Initially algin was used to control viscosity in a gasket compound for sealing tin cans, but Kelco has developed many other applications for it because of its importance to industries as a highly efficient thickening, stabilizing, suspending and gelling agent.

Algin is now used in a wide range of foods including desserts, gels, milkshake mixes, dairy products and canned foods. It is used in bakery products from cake mixes to meringues to improve texture and retain moisture. Algin is used in frozen foods for its stabilizing properties to assure smooth texture and uniform thawing. It is also used to stabilize beer foam. The primary industrial applications for algin are in paper coating and sizing, textile printing and welding-rod coatings. Pharmaceutical and cosmetic applications for algin include its use in products including tableting, dental impression compounds (if you don't use it in your toothpaste!) and anti-acid formulations.

Products which are listed to contain derivatives of kelp and other algae include the following. Dairy products such as Carnation low-fat chocolate milk, Lucerne whipping cream, Lucerne cream topping, Hershey's chocolate milk, Lucerne chocolate milk and Knudsen chocolate milk all contain carrageenan. Baby formulas including Similac and Enfamil contain carrageenan. Milkshake mixes like Ovaltine contain carrageenan. Pudding mixes including Jello Pudding & Pie Filling contain carrageenan. Yoghurts including Yoplait and Continental brands contain agar. Creamed cottage cheese from Weight Watchers and Lucerne contain carrageenan. Schilling sour cream sauce mix contains algin. Party dips such as Safeway Jalapeno, Safeway Garlic, Safeway Onion, and Imo Green Onion Dip all contain algin while Hidden Valley Party Dip contains carrageenan. Ice creams including Lucerne, Diet Count dietetic ice cream and Carnation contain carrageenan. Desserts such as Duncan Hines brownie mix contain carrageenan. Salad dressings including Wishbone Deluxe French, Wishbone Blue Cheese, Wishbone 1000 Island, Kraft Rancher's Choice, Kraft 1000 Island, Kraft Italian, Kraft Creamy Cucumber, Girards Cilantro, and Girards Rancho California all contain algin while Hidden Valley Ranch contains carrageenan. Frozen foods such as Bel Air Onion Rings contain algin. Toothpastes including Colgate use carrageenan. Sauces and toppings such as Bob's Tartar Sauce contain algin while Lawry's Alfredo sauce mix and Kraft horseradish contain carrageenan. Frozen desserts including Weight Watchers chocolate mouse, Sara Lee Black Forest Cake, and Sara Lee cheesecake contain algin while Fudgsickles have carrageenan in them. There are numerous brands of sea kelp shampoo and facial soap. Kelp vitamin tablets are also found in health food stores. Fruit drinks such as Sunny Delight Citrus Punch contain algin.


This page written by Dr. William W. Bushing. Bill has conducted substantial research on the kelp surrounding Catalina and the other Channel Islands. His focus has been on the use of drifting kelp as a dispersal mode from the mainland to the islands for marine invertebrates and small fishes, and on the persistence (distribution patterns over time) of kelp around Catalina. He has presented his research at a range of regional, state-wide, national and international conferences and published a number of research papers in scientific journals. He is an authority on the use of satellite remote sensing, and a pioneer in the use of GIS (geographic information systems), to study kelp.

Photographs for this Web page were provided by Dr. Bushing; Dr. Dan Reed and Dr. Mark Carr of the Marine Science Institute, University of California, Santa Barbara; and Dr. Ray Lewis of the University of Nebraska.