Fast-growing kelp invades San Francisco Bay

SAN FRANCISCO — A fast-growing kelp from the Far East has spread along the California coast from Los Angeles to San Francisco Bay, worrying marine scientists and outpacing eradication efforts.

In May, scientists for the first time found the invasive seaweed called Undaria pinnatifida clinging to docks at a yacht harbor in San Francisco Bay, fouling boat hulls and pier pilings.

“I was walking in San Francisco Marina, and that’s when I saw the kelp attached to a boat,” said Chela Zabin, a biologist at the Smithsonian Environmental Research Center in Tiburon, Calif.

“It was 6-foot long, and there is nothing here in the bay that gets to that size,” Zabin said. “I didn’t want to believe what it was, it’s depressing.”

Before Zabin’s discovery, ocean scientists believed the northward spread of the invasive kelp had been stopped at Monterey Bay. But last year, federal funding used to buy equipment for volunteer divers dried up, reducing the number of people working on eradication.

The seaweed — known as wakame by Japanese food lovers and used in miso soup — was first discovered in Los Angeles Harbor in 2000.

A year later, the kelp, which can grow an inch a day as it creates dense underwater forests, showed up at Catalina Island, off the Los Angeles coastline, and Monterey Bay.

Studies have concluded the kelp was likely introduced to California by accidental transport on shipments of oysters, vessel hulls and people who cultivated it in the region for cooking.

On Thursday, four divers spent hours at Pier 40 on San Francisco’s Fisherman’s Wharf peeling pieces of kelp off of the docks, yachts and pier pilings. But few believe the effort removed all traces of the seaweed. Scientists will be checking monthly for signs of further spread.

“On any invasion, the window of opportunity to successfully eradicate that species is usually narrow,” said Steve Lonhart, one of the divers and a senior scientist with the Monterey Bay National Marine Sanctuary.

“You want to do it as soon as it becomes established. The longer you wait, the less chance for success,” he said.

The seaweed concerns marine biologists because it can damage fragile ocean ecosystems by choking off the sunlight needed by native kelps. The native kelp forests provide key habitat for otters, fish and other marine life.

The seaweed spreads by releasing millions of spores that can be dispersed by currents in the open ocean, but in a protected marina lighter currents could slow its reach. While it is native to Japan, China and Korea, studies have found the kelp in the Mediterranean Sea, the Atlantic Coast of Europe, New Zealand and Argentina.

“If it’s restricted to two docks in the marinas in San Francisco Bay, we’ll have a chance,” Zabin said. “If it’s spread beyond those places, it may be a lost cause.”

Because of its wide range, it has been nominated as among 100 of the world’s worst invaders, according to the Global Invasive Species Database.

Though Thursday’s dive may remove the immediate threat to the bay, Lonhart believes they are fighting a losing battle against a persistent pest.

“In 10 years I’m guessing Undaria is going to be all over the place. It’s not a problem getting smaller in scope, it’s getting worse and worse,” he said.

Scientists say the waters from Baja California to British Columbia are the perfect temperature for Undaria to spread even further up the Pacific Coast of the United States.

For about six years, the National Oceanic Atmospheric Administration had organized monthly volunteer diving efforts to yank the stubborn kelp out of Monterey harbor to help root out the kelp.

The program helped, but it failed to stop the kelp from entering San Francisco Bay, scientists say.

“This is not well studied enough, and we’re really quite nervous about it getting out in the ecosystem,” Zabin said. “It will attach to about anything.”