John Upton/The Bay Citizen

Dock Attendant Joe Monroe removes invasive kelp from South Beach Harbor, which is wedged between sites that will be used for America's Cup activities

The America’s Cup could spread something far more destructive across San Francisco Bay than tourists and fast-moving catamarans.

While residents on Thursday will discover the extent of traffic and transit havoc that will be wrought by the event, environmentalists have been warning city and port officials that the regatta will provide an aggressive form of invasive algae with a free ride throughout the region.

The invasive kelp, which was first detected along city shorelines in 2009, could multiply explosively, spread throughout the bay and choke out native seaweed species when event-related demolition and boat removal activities begin a year from now, a coalition of environmental groups is warning. The issue was first raised during a Feb. 24 meeting about the event's environmental impacts and has been discussed in private meetings since then.

Undaria pinnatifida is a fast-growing seaweed that’s believed to have spread in crevices on ship hulls traveling from their native East Asian habitat to Long Beach and then north to San Francisco Bay, according to Chela Zabin, a Tiburon-based Smithsonian Environmental Research Center scientist who found the rugged seaweed in San Francisco two years ago. The alga, an ingredient in miso soup, is cultivated throughout Asia for human consumption.

Since it was discovered here, the seaweed has spread rapidly throughout the San Francisco Marina and South Beach Harbor. Scientists worry that it could destroy native kelp populations that provide habitat and food that are better suited to native bay wildlife.

Officials and volunteers are attempting to control the undaria by yanking it out from underneath piers, hulls and ship moorings. 

“Lots of species, both invertebrates and fish, are dependent on feeding or using some of the native species of kelp or algae for food or shelter,” Zabin said.

The wiry vegetation, which can grow to more than 10 feet long, has not spread to the East or North Bay — but that could change as America’s Cup organizers begin their preparations, according to Zabin and the nonprofit organization Baykeeper.

Vanessa Guerra

Chela Zabin removes invasive kelp from Pier 40

The algal invader could continue its northward march by clinging to the hulls of little-used boats as they are relocated from their city moorings to other parts of the region to make way for America’s Cup demolition and construction activities, according to Zabin.

Furthermore, thick clouds of spores could be released from large, sexually mature kelp weeds believed to be lodged under piers when those structures are demolished to make way for event facilities, according to Deb Self, executive director of Baykeeper.

“It multiplies pretty rapidly once it reaches sexual maturity,” Self said. “They’re going to have to do something to prevent a massive release of spores.”

Kelley Capone, a Port of San Francisco environmental regulatory official working on the America’s Cup, said it’s unclear right now how the release of spores could be controlled but that the matter is being investigated as part of the event's environmental review.

Fine mesh might be used to surround in-water construction sites to protect wildlife from noise impacts of pile-driving and other activities, and that netting might also be used to prevent kelp spores and mud from spilling out into the environment, according to Capone.

“We’ve going to try to look at the whole world of impacts,” Capone said.

Correction: A previous version of this story indicated that undaria pinnatifida had harmed native kelp populations in San Francisco Bay. There have been no studies of the kelp's effect on native species here yet, but the seaweed has been demonstrated to impact native algae in other parts of the world where it has been studied.