(07-09) 17:30 PDT -- Four divers led by a land-based ecologist hunted the turbid waters of San Francisco's South Beach marina Thursday for a nasty, invasive seaweed that is taking over harbors and estuaries all along the Pacific coast.
Although their prey didn't seem to have a chance, the divers could hardly keep up with the abundant infestation of what in more benign coastal environments is a tasty ingredient of miso soup.
At Pier 40 along the marina's concrete dock for visiting yachts and from the hulls of the boats themselves, the divers stripped off yards of the kelp in small chunks. They harvested 2-inch-long golden brown juvenile algae, and long strands of the dark brown mature kelp, their broad rippling leaves holding clusters of reproductive spores ready to spread through the water and give birth to still more invaders.
Steve Lonhart, a senior scientist and diver from the Monterey Bay National Marine Sanctuary, has been battling the invasion in the bay since the alien kelp species was discovered on boat hulls in the San Francisco marina in May.
"It's still there and no one thinks it will be completely eradicated, but hopefully we can keep it from spreading," said Lonhart as he put on scuba gear before his first dive.
The invading kelp is called Undaria pinnatifida, a seaweed species known popularly in Japan as wakame. Believed to have arrived on the hulls of commercial ships, the kelp has plagued harbors in Southern California since 2000 and arrived in the bay more recently.
"The kelp is a serious threat to our native species because it crowds them out and deprives them of oxygen, so it ruins the natural habitat for native species of fish, shellfish, sea otters and other marine organisms," said Chela Zabin, an ecologist with the Smithsonian Environmental Research Center in Tiburon who with her assistants keeps meticulous records of every alien cluster the divers harvest.
"What we want to do is to alert boat owners - particularly those sailing into the bay from southern harbors - to watch for the seaweed fouling their hulls and get rid of it. But not in the water!" she said.
Although the kelp is tasty food in Asia, it is dangerous to eat here, Zabin said, because it gathers up all the toxins in the murky, polluted waters of harbors along the California coast - including the bay.
Other divers in the project that will continue until the South Beach marina is clear include Chad King, a biologist from the Marine Sanctuary, Gail Ashton of the Smithsonian Center, and Christopher Scianni of the California State Lands Commission.