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 six-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 funding for eradication dried up last year, forcing federal officials to rely on volunteers.

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.

"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."

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.