Kelp Keeping a Forest Afloat

Can California save its vital, vanishing towers of giant seaweed?

  • Michael Tennesen
  • Apr 01, 1992
Sunlight filters through the dense canopy, throwing eerie, flickering shadows on the forest floor. Slender, twisted towers soar upward from the rocks below, providing shelter for countless plants and animals. Concealed in a cave, a toothy predator eyes its prey, which gropes for balance in the violent force of a winter storm. With imperceptible speed, the predator darts from its hole, seizes the smaller animal and, in a gulp, devours it.

An ordinary event in the forest? Perhaps, but this is no ordinary forest. It is one of the wildest, least-explored wilderness areas in the country, and its edge lies a mere hour's drive from downtown Los Angeles.

Neither redwood nor pine, the "trees" in this majestic forest are the vinelike stalks of giant kelp--Macrocystis pyrifera--world's largest seaweed. And just like an above-ground woodland, this undersea forest is a bustling, fertile ecosystem that serves as an essential habitat for a network of interdependent plants and animals.

California's kelp forest--which grows to depths as great as 130 feet along the coast and around offshore islands--supports more than 800 species of marine life. Sprawling across 44,000 acres of ocean floor, the forest offers something for everyone: food for crustaceans, shelter for juvenile fin fish and hunting grounds for seals and sea otters.

Over the past decade, natural and manmade forces have cast a shadow over the health of California's kelp. Winter storms and two episodes of unusually high water temperatures (the so-called El Niño phenomenon) decimated the forest. What's more, a plague of sea urchins mowed thousands of acres of the seaweed to stubble.

Now, however, the kelp is slowly beginning to rebound, thanks largely to state efforts to control urchins and pollution. That's good news, say scientists, who are discovering just how vital the plant is to the region's near-shore ecosystem. "What happens to the kelp," explains Ken Wilson, a biologist with the California Department of Fish and Game, "affects the marine community throughout the state."

Giant kelp grows in temperate waters off South Africa, Australia, New Zealand and South America, and in North America its range extends from Alaska to the coast of Mexico. Nowhere in this hemisphere, though, are the kelp forests as lush as those off the coasts of California and Northern Baja in Mexico. John Pearse, a biologist with the University of California at Santa Cruz, found that a 1,100-square yard plot of giant kelp he was studying off the coast of Santa Cruz supported more than 67,000 animals.

Like a rain forest, the kelp "jungle" consists of several distinct levels, and different species are associated with each level. At the base of the plants are the "holdfasts." These intertwining, rootlike strands anchor the kelp to the bottom and provide habitat for more than 175 marine species, including sea anemones, brittle stars and juvenile abalone.

Just above the hold-fasts are the midwater fronds, long stems with leaflike blades held upright by tiny gas-filled bladders. Here, juvenile fish seek refuge from predators. Young gray whales returning from calving grounds off Baja California also hide among the kelp from killer whales, whose sonar signals are broken up by the curtain of vegetation.

Dense canopies of kelp at the surface form buoyant mats upon which snowy egrets, great blue herons and gulls perch to stalk fish below. Otters coil up in the kelp to anchor themselves in the current or tie up their pups while foraging for food.

A single kelp plant can live as long as six years, but the branches and leaves of the upper canopy break off after six months and become what is known as drift. This drift in turn becomes food for abalone, urchins, snails, worms and sea cucumbers. Scientists from California's Monterey Bay Aquarium have found that every year waves and currents sweep more than 100 tons of drift from the lush, 1,800-acre kelp forest off Monterey Bay onto sandy shores, into tide pools and far out to sea. "With underwater remote cameras we've located kelp drift 65 miles offshore in depths of 3,800 yards," says aquarium Director Chris Harrold.

Over the years, people have also found a number of uses for kelp. During World War I, for example, the Hercules Powder Company near San Diego extracted potash and acetone from kelp to manufacture gunpowder.

Today, thresherlike boats harvest more than 160,000 tons of California kelp every year for the production of algin. This kelp extract is used for everything from strengthening ceramics, improving the consistency of plaster thickening jams and making smoother ice cream to putting a head on beer.

More uses for kelp may soon be added to the list. Scientists at the Marine Biotechnology Seawater Laboratory at the University of California at Santa Barbara, for instance, are investigating whether methane gas produced by kelp fermentation can be used to create an alternative source of energy to fossil fuels.

And at the California Institute of Technology, environmental engineer Wheeler North is trying to generate government interest in using huge mid-oceanic kelp "farms" to soak up atmospheric carbon dioxide and counteract global warming. "One hundred farms, a hundred miles on each side [a million square miles] would take up two-thirds of all the carbon dioxide produced by today's fossil fuels," North claims.

For the time being, though, the plant's greatest value is to the wildlife that depends on it. Just how important the kelp forest is to the marine community was made clear during the winter of 1982-1983, when California's coast was clobbered by the most severe El Niño on record. (El Niño is a warm current that occasionally rises up from equatorial waters and replaces the normal, cooler Alaskan currents, wreaking havoc with the weather and the environment for thousands of miles.)

Violent storms wiped out as much as 90 percent of the state's giant kelp forests. Rising sea temperatures depleted nutrients, inhibiting kelp production and causing huge plankton and fish kills. Commercial fisheries for abalone and other species that are dependent on kelp fell as much as 30 percent.

At first, sport fishermen were rewarded by a bonanza of tropical fishes that came with the warm water currents. But as El Niño subsided and temperatures returned to normal, fishing got worse, especially in areas where the kelp was slow to recover. "And it stayed bad for a long time," says Roger Wood, captain of a sport-fishing boat based in Santa Barbara. "Any time you reduce the kelp habitat, it's going to affect the fishing."

Most of California's kelp had recovered within two years. (A recurrence of El Niño last winter was moderate, say scientists, and not expected to cause much damage in this country.) But a once-flourishing, 8,256-acre patch off the coast of Santa Barbara-18 percent of the state's kelp forest--has yet to revive. "People think, 'Well, that's just in Santa Barbara, so we don't have to worry about it,' " says Wilson. "But that's not true. The loss of that forest has had implications for fishing throughout Southern California."

In a normal system, kelp attaches itself to the rocky ocean floor, which provides stability in stormy seas. But the forest developed differently on the smooth, sandy surface off Santa Barbara's coast. The first plants anchored themselves onto worm tubes (the paperlike sheaths of sea worms). Newcomers latched onto these pioneers and eventually to each other.

With such a tenuous foothold, the kelp forest was more easily stripped away by El Niño 's powerful storms. State officials, hoping to rebuild the forest, hired a private kelp-harvesting company called the Kelco Corporation to undertake a kelp transplant. The company tried a number of techniques, such as putting out mushroom-shaped slabs of concrete and sections of chain-link fence to serve as kelp anchors.

But in 1988, the biggest storm to hit the area in a century (though unrelated to El Niño ) knocked the struggling forest back to square one. Kelco tried again, but this time the threat came from kelp's old nemesis, the sea urchin.

Normally, as in Central California, sea urchins hide in the cracks and crevices of reefs, helping themselves to bits of kelp that float by. Natural predators such as sea otters, which can consume as much as 25 percent of their weight in prey, usually keep the spiny creatures in check.

But in Southern California, there have been no otters since furriers hunted the animals to near-extinction in the early 1800s. Free of otter predation, urchins began to multiply and, in some cases, devour enormous stands of kelp.

The Urchins have been especially troubling to Southern California's kelp since the 1950s, when cities along the coast pumped untreated sewage into the sea forests. The pollution decreased water clarity and inhibited plant growth. But urchins prospered, impervious to the waste. Marching and mowing in slow-motion battalions as dense as 200 per square yard, they leave behind a swath of destruction called an "urchin barren." Biologists tried poisoning them with quicklime, and even sent volunteer divers to crush the pests with hammers.

Communities in Southern California have improved their sewage treatment and are now pumping wastes farther offshore. Still, there remains the problem of too many urchins and too few predators.

Spiny lobsters and sheephead (fin fish that can weigh 35 pounds or more) once helped keep the area's urchins under control. That was until about 40 years ago, when these predators themselves became prey to human divers hunting for food and trophies.

Sea otters recently transplanted from Central California to San Nicholas Island farther south as insurance against a population crash may provide some relief. But as a concession to abalone fishermen, the mollusk-loving animals are restricted to waters near San Nicholas. If caught elsewhere, they are captured and shipped back to Central California.

It looks now as though the best urchin predators may be the two-legged kind. In recent years, the Japanese appetite for urchin roe, a delicacy called uni, has turned the creatures into California's largest fishery, boasting revenues of more than $23 million in 1989. That same year, urchins ranked second only to kelp (a $40-million industry) as the state's most important marine resource.

Despite lingering worries about Santa Barbara's kelp, many biologists remain optimistic about the long-term prospects for the health of the undersea forest. "If you had asked me 20 years ago, I would have said the future of California's giant kelp looks bleak," says Wheeler North. "But today the public is concerned; people realize what a valuable resource they have. And the fact that the state is out there spending money trying to reforest the kelp . . . well, it's a good omen."

Writer Michael Tennesen frequently swims and fishes among the kelp forests near his Southern California home. San Fransisco Bay Area photographer Norbert Wu is the author of Beneath the Waves (Chronicle Books, 1992), a children's book about kelp forests.

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