Wakame, the seaweed salad offered on menus at sushi restaurants, is also an invasive kelp from Asia known as Undaria pinnatifida that’s threatening the underwater ecosystem of Pillar Point Harbor in Half Moon Bay.
The long, wavy greenish-brown kelp found dangling off the docks and boats in the marina looks like it belongs there, but it’s actually a marine invasive species that attaches to anything in the water, outcompeting the native kelp that some fish need for shelter, food and egg-laying.
Since its discovery in Southern California in 2000, undaria has spread north with small populations found in more recent years in San Francisco Bay and Pillar Point Harbor. Up until now, control has mainly been a volunteer effort, surveying locations and then pulling it out.
Recently, however, marine biologist Chela Zabin with the Smithsonian Environmental Research Center has organized with an invasive species management coalition, Bay Area Early Detection Network (BAEDN), technical support and funding to spot and remove undaria in Bay Area locations such as the San Francisco Marina and Pillar Point.
One of BAEDN’s high priority spots is Half Moon Bay, where the population quickly expanded before its discovery.
Once a month, BAEDN volunteers are at the harbor to do removals and collect data on the undaria they remove. With the expected arrival of a federal fisheries grant for just under $20,000, BAEDN plans to fund the coordination of boaters, divers and anyone who is interested in volunteering time and effort to control the spread of undaria in San Mateo County.
“The population at Pillar Point is small relative to locations in the San Francisco Bay and Monterey and has not spread much in the two years we've been working to remove it,” said Zabin.
Still, undaria could be difficult to uproot if its growth is not managed regularly since it reproduces by spores and spreads through the water very easily.
“It's always harder to eradicate after an invader has really become abundant and widespread,” said Zabin. “But in this entire time, we have found it only on a few docks and nowhere else in the harbor. These two facts make us more confident that it is not too late to get rid of it via hand removals.”
The population of undaria in Pillar Point Harbor has fluctuated widely, and "Zabin has noted that the seaweed has done well at Pillar Point Harbor due to the clean water environment here," said Scott Grindy, harbormaster of the San Mateo County Harbor District.
Zabin and her volunteers have gone as long as six months without finding any only to have it bounce back in high abundance later in the year. The growth does not seem particularly tied to any seasonal changes, she said.
“Undaria appears to be spreading along the Coast mostly by recreational boats, such as yachts, and perhaps by regional fishing vessels, rather than in the ballast tanks of large commercial cargo vessels,” she said.
BAEDN volunteers are needed to help in the monthly undaria removals. The group works mostly from dockside and kayakers are welcome because there are extensive seawalls at Pillar Point that can really only be accessed by small boats, including paddle boards.
“In the past, we've had kayakers check the seawalls for undaria. They didn't find any, but we really could use help to survey these areas again,” said Zabin.
Boaters can also help by checking their boats for undaria and removing it if they find it before they leave Pillar Point to travel to other harbors.
“If they spend time in Monterey or Southern California where there is a lot of undaria,” said Zabin, “they should probably check and clean before returning to Pillar Point to prevent re-introducing it.”
To join the volunteer effort to detect and control this invasive kelp, call (415)-435-7128 or e-mail firstname.lastname@example.org.
Information in this article was originally sourced from a Bay Nature article by Elizabeth Laubach published on Aug. 15, 2012.