Marine Scientists Seek Help For Shrinking Undersea Kelp
Warming seas and fishing harm seaweed forests off California's coast
LA JOLLA, CALIF.
Slipping daily into an undersea forest of kelp off San Diego's Point Loma, a team of wet-suited divers tallies the plants and creatures it finds in a biologist's variation of Dr. Seuss's "One Fish, Two Fish, Red Fish, Blue Fish."
For more than 20 years, the researchers have been tracking shifts in marine life and in the gently swaying seaweed. As they read the record written in their submarine forest, they are finding signs that gradually warming seas and poorly regulated fishing practices are putting the squeeze on an ecosystem valued for its biological wealth and for the money it generates from fishing and kelp harvesting.
The team's work cuts to the heart of debates currently under way in Sacramento, Calif., over tightening the state's marine conservation regulations. One area of concern is the state's beleaguered kelp forests.
A diverse and productive habitat
Since the days of naturalist Charles Darwin's voyage on the HMS Beagle, these aquatic equivalents of terrestrial forests have fascinated biologists.
Sheltering, feeding, and hiding a range of organisms, from abalone and sea urchins to bass, sheepshead, and sea otters, kelp forests "are a wonderfully diverse and productive habitat," says Mia Tegner, a marine biologist at the Scripps Institution of Oceanography here who leads the Point Loma research effort.
The forests' influence reaches beyond their boundaries. Tides and currents flush them of organic debris, which enriches the food chain in surrounding waters.
Point Loma's forest, which covers 8 square kilometers (3 square miles), is dominated by the giant Macrocystis pyrifera, a kelp that anchors itself on the sea floor at depths of from 4-1/2 to 18 meters (15 to 60 feet), then rises until its stalk-like stipes reach the surface. In North America, the giant kelp species is found only off the West Coast and ranges from Baja California north to Santa Cruz. Vast stands of these giant seaweeds also grow off the coasts of Tasmania, South Africa, the tip of South America, and near islands off Antarctica.
Ms. Tegner began her work in kelp forests in the early 1970s studying the biology of sea urchins, which are considered delicacies in Asia, particularly in Japan. Currently valued at $75 million a year, sea-urchin harvesting surged in the late 1980s to become California's largest fishery, according to industry figures.
Her work on sea-urchin ecology, she says, expanded to the entire kelp forest as ecologists realized that to manage individual species, they had to manage their ecosystems. For Tegner and her colleagues, that meant not only two to three dives a day, but also combing nautical records as far back as 1857 for clues about the kelp forest's past size.
One of the most striking patterns they found involves the forest's response to El Nios, the periodic spread eastward of warmer-than-usual surface water from the western tropical Pacific.
"What we're finding is that kelps are hugely affected by processes across the entire Pacific Ocean," Tegner says. The 1982-84 El Nio, the strongest on record, all but wiped out the Point Loma forest by reducing the nutrients available to the kelp. Meanwhile, the 1992-93 El Nio stalled the forest's steady recovery.
Longer-term warming patterns are also troubling. Since 1957, an index based on stipe counts, which Tegner and her colleagues developed to measure the Point Loma kelp forest's carrying capacity, has fallen by two-thirds. This, she says, closely tracks with a gradual increase in sea-surface temperatures.
Noting that this year, another strong El Nio is in the offing, David Duggins, a marine biologist at the University of Washington's Friday Harbor Laboratory on Puget Sound, adds that if climate warming brings longer-lived, more severe, or more frequent El Nios, this "could wreak havoc with the kelp-forest system."
Damage from fishing
Against the backdrop of climate-related stress on the forest comes the damage from commercial and sport fishing.
Tegner cites sheepshead as an example. The colorful - and tasty - fish feed on sea urchins, which feed on kelp, in effect clear-cutting the forest by cutting kelps' stipes off at the base. Sport divers wielding spears have reduced the number of large sheepshead, the aquarium industry captures the juveniles, while the Asian restaurant and export markets pay top dollar for 1- to 3-pound, pre-productive females.
The danger for the kelp forest: Cut too deeply into the population that helps keep urchins in check and the once-productive forest becomes a shadow of its former self.
"It's a classic example of a lack of [fisheries] management with huge implications for the whole kelp community," Tegner says. In the past year, she adds, her research agenda has shifted to include more emphasis on helping to build a scientific basis for managing kelp-related fisheries.
Unlike terrestrial forests, refuges and preserves for kelp forests are few, far between, and poorly managed, she contends. The challenge is trying to overcome shrinking expectations as successive generations of marine biologists tend to use the already degraded kelp-forest habitats they first see as the basis for determining what's "natural," she says.
With kelp forests already under climate-related assaults, poorly managed fisheries could become "the straw that broke the camel's back," says Dr. Duggins. "When you pile disturbance on top of disturbance, they exacerbate one another."