Dec

When kelp attacks: Repelling invaders with hand-to-hand combat

Try as they might, scientists can’t anticipate the outcomes of their research. The pursuit of one question often produces unexpected discoveries. Chela Zabin knows this first-hand.

Zabin is an ecologist in the Smithsonian Environmental Research Center’s marine invasion research program, led by senior scientist Greg Ruiz. She operates out of Tiburon, Calif., on the shore of San Francisco Bay—the most invaded estuary in the country. For more than a decade, SERC researchers at this facility have been documenting the patterns, causes and effects of biological invasions by non-native species.

Undaria is easily recognized by its reproductive structure, which resembles a ruffled Elizabethan collar. (Photo courtesy of Chela Zabin)

Last May, Zabin and her colleagues were out walking the docks of the San Francisco Marina Yacht Harbor. Their mission was clear: divide boats into categories according to the amount of life found growing on their hulls. Yachts with lots of barnacles and algae were given a score of five; those with clean hulls received a zero. Simple enough.

Boat by boat, they called out numbers. And then Zabin spotted a “beautiful golden-brown” seaweed—Undaria pinnatifida—and a big problem. “I looked at it and had an immediate feeling of dread,” Zabin recalls. She recognized the kelp by two of its hallmark traits. First, it dwarfed the marina’s other algae; Undaria can grow up to three meters tall. Second, its reproductive structure—the sporophyll—has a folded-spiral shape that Zabin says looks like an Elizabethan collar.

Undaria’s native territory is the waters off Korea, China and Japan where it forms entire underwater forests. It has also found its way into the regional cuisine. The Koreans call it miyeuk and the Chinese, haijiecai. And if you’ve ever ordered a wakame salad at a Japanese restaurant, you’ve tasted Undaria.

The first recorded occurrence of Undaria in the United States was in 2000, when it was spotted in the Los Angeles Harbor. Since then, its range has expanded northward along the California coastline. Zabin and others knew it had made its way to Monterey. But her May 8, 2009 discovery proved that Undaria’s reach had advanced 105 miles in nine years.

Chris Brown with a specimen of the kelp that he and his colleagues have been removing by hand from marinas on the San Francisco Bay. (Photo courtesy of Chela Zabin)

There’s nothing inherently wrong with Undaria, but for Zabin and others concerned with preserving biodiversity, it poses a potential threat to California’s native algae. Its rapid growth and fouling potential could also cause economic problems for marina operators and oyster growers alike.

After spotting the kelp in San Francisco, Zabin, along with SERC colleagues Gail Ashton and Chris Brown, went into emergency mode. They quickly surveyed eight additional marinas and harbors in the area. They found Undaria dwelling in one-third of the locations. The alga isn’t picky. I can attach to almost any hard surface. So Zabin wasn’t surprised to find it growing on boats, ropes, docks, pilings and tires.

To make matters worse, most of the Undaria Zabin found were reproductive. The spores they release only float around for a short while before they attach to something solid. In the San Francisco Bay, the hulls of large ships and small boats offer plenty of surface area for Undaria to latch onto.

Zabin is preoccupied with boat hulls because they offer hitchhikers, like Undaria, lifts to new habitats. More than 3,000 commercial vessels visit the San Francisco Bay annually. And local residents have registered 150,000 private boats. All those boats combined with the fact that Undaria could find suitable habitat as far north as Alaska, prompted Zabin to take immediate action.

“We didn’t just grimace and let it go,” she says. Since the May discovery, SERC staff have been removing Undaria—by hand—at the infected marinas. Zabin has enlisted help from concerned citizens as well as scientists from other academic and government institutions. The underwater weeding has produced mostly positive results so far. Zabin has observed declines in Undaria at two of the three marinas.