Death for the killer seaweed

Last month, researchers began a campaign to eradicate several dozen patches of rogue algae in a California lagoon (SN: 7/15/00, p. 36: Ultimate Sea Weed Loose in America). These Caulerpa taxifolia represent the same aggressive weed, an aquarium-derived mutant, that is smothering life along the Mediterranean seafloor.

Under the direction of state and federal regulators, biologists are carefully enclosing each stand of the lagoon’s clones with a tarp and then pumping in chlorine. Patches the size of a person’s hand should succumb to a few weeks of the chlorine bath, says Robert Hoffman of the National Marine Fisheries Service in Long Beach, Calif.

Routing the few far bigger patches could constitute a real challenge, he notes.

Though the alga’s 14-inch-tall fronds take up the poisonous chlorine, Hoffman worries that the rootlike structures that anchor the weed could survive beneath the fine sediment. So, his team is considering following up the chlorine treatment with a vinegar chaser. Hoffman says the acetic acid may remain toxic far longer than chlorine, polishing off any lingering algae.

Because even a small piece of the weed can seed a new stand of this Caulerpa, Hoffman says, biologists won’t try to remove the algal invaders until they’re dead. In fact, “for the largest patches,” he says, “the tarps may never be removed.” Workers may just bury them under a permanent layer of sediment below the water.