A highly invasive form of brown kelp native to Japan has spread throughout the San Francisco waterfront since it was discovered three years ago and could threaten native species and ecosystems if money and resources aren't put into stopping its spread, researchers say.

The seaweed, commonly known as Wakame, multiplies at a feverish rate, and has driven out native kelp and drastically altered entire ecosystems in other places, including Argentina, New Zealand and parts of Europe.

The alien kelp, which is a common ingredient in miso soup, was discovered in 2009 at the San Francisco Yacht Harbor, in the Marina, and at the South Beach Harbor near Pier 40, prompting widespread alarm and a concerted effort by marina workers and biologists to get rid of it.

The watery weed, known in scientific circles as Undaria pinnatifida, can attach itself to almost anything - pilings, boats, docks, chains, riprap - and grow an inch a day, with individuals sometimes stretching 9 feet or more across. It likes cold water as low as 32 degrees Fahrenheit, but also thrives as far south as Baja California, where the water is 10 degrees warmer than it is in the Bay Area.

Spreading northward

The algae species, recognized globally as one of the world's top 100 invasive species, was introduced to California about 12 years ago, probably by a ship that moored in the Long Beach area. It was discovered in Monterey in 2001 and in Mexico in 2002. It has since spread northward along the coast, most likely by hitching rides on boats.

Last year, researchers with the Smithsonian Environmental Research Center found it clinging to piers and docks in several more places along the San Francisco waterfront, including Fort Mason, Pier 39, Fisherman's Wharf and along the Hyde Street pier. The infestation had gotten worse near AT&T Park and at Pillar Point Harbor, in Half Moon Bay.

"In San Francisco Bay, it is now widespread enough, and on so many pier pilings that we can't get to, that I don't think we can remove it by hand," said Chela Zabin, a biologist for the Maryland-based research center and the UC Davis. "It's a potentially very serious problem."

Zabin, who works out of a Smithsonian satellite office at the Romberg Tiburon Center for Environmental Studies in Marin County, said the removal effort faces several obstacles, not the least of which is that there is no money available for research or to pay for an eradication effort, making it an all-volunteer affair.

Elimination challenge

She and biologists with the Aquarium of the Bay near Pier 39 regularly go out looking for the slimy blooms, but even if there were enough workers and funding, total elimination would be a tricky proposition. The species shoots out thousands of microscopic spores that can remain dormant for up to two years, she said.

"We pull out the large sprouts, but any time we find one that has released spores it sets the clock back for two years," Zabin said. "Another problem is that the water in San Francisco Bay is very turbid and, a lot of times, even if it is only 2 feet below the surface, we can't see it. So it's a challenge and even if we were getting rid of every single individual we'd still have that two-year lag time, and that's assuming another boat doesn't come in and reinfect the area."

The weed can be killed by containing the infected area and immersing it in fresh water or by subjecting it to heat. The problem is, those tactics cost money.

Zabin said if the spread of the seaweed is not checked, it could eventually outcompete the native seaweeds, including giant kelp, the majestic floating seaweed species common to Monterey Bay whose limbs can reach 200 feet below the surface. Many fish and other aquatic animals depend on the giant kelp for food, shelter to lay eggs on or to escape from predators. These functions cannot be replaced by Undaria pinnatifida, which is more like a giant banana leaf that sinks below the surface and attaches itself to things, Zabin said.

"We don't want to overstate what it is going to do," Zabin said, "but there is enough evidence from around the world to know that it can be very disruptive to natural areas and negatively affect native species."
