Usually, the first weekend of April is when abalone divers pack up their wetsuits and fins and head off to campsites along the Sonoma and Mendocino coast. However, this year’s recreational abalone season is closed due to a population on the brink of collapse, so the diving community has rechanneled its efforts in a seemingly mad scheme to save the abalone, involving underwater vacuums, hookahs and purple sea urchins.
The urchins are an overpopulated species that has laid waste to the struggling kelp forests that abalone and other marine wildlife need for food. In response, fans of recreational abalone diving are paying professional divers to literally vacuum up the spiny creatures — which have little commercial value — from the sea floor with a fiberglass pipe that empties into a big net.
Diving associations, along with marine conservation and education organizations like the Noyo Center for Marine Science in Fort Bragg and Get Inspired in Southern California, have raised $80,000 to fund a California Department of Fish and Wildlife project to remove purple sea urchins from select areas of the Northern California coast.
“There’s no way we could get rid of them all,” said Joshua Russo, a diving instructor and president of the Watermen’s Alliance, a diving and spearfishing association. “We’re not trying to. We’re trying to get rid of them at specific locations to allow the kelp to grow back.”
California Department of Fish and Wildlife scientists have been planning this urchin removal experiment since 2016 in response to the dearth of bull kelp. The kelp forest supports not just abalone but also red sea urchin (which is fished commercially and often seen on restaurant menus), smaller fish and invertebrates that provide food for larger fish, like salmon. One of the big causes of decline in the kelp forest was the 2014-15 El Niño, which raised ocean temperatures and discouraged new growth. The Northern California kelp forest shrank by 93 percent between 2008 and 2014, according to aerial surveys conducted by the department, which has not seen much improvement since.
“I don’t expect to see a recovery in kelp until we see a decline in purple urchin,” said Cynthia Catton, an environmental scientist with the department’s marine region, based at the UC Davis Bodega Marine Laboratory. She estimates the invertebrate’s population at 60 to 100 times its normal size. “We’ve been learning a lot in the last couple years about how much effort it’s going to take to control the purple urchin.”
The purple urchin has few natural predators. The sea star that normally eats them died off from disease suddenly in 2013, the North Coast sea otter population hasn’t recovered, and humans prefer the meatier red urchin. And, unlike abalone, purple sea urchins reproduce well even under starvation conditions.
“They’re really hardy, and there isn’t much to them — they’re just a big calcified ball of water and spines,” Catton said. “They out-compete everything else for food that they munch on. If there’s absolutely no food out there, they can get nutrients from the water.”
The purple urchin infestation has had economic as well as ecological ramifications. Recreational abalone diving normally brings an estimated $44 million annually in tourism into North Coast towns, according to a department analysis. The Northern California commercial red sea urchin fishery, which was worth $3.6 million in 2013, dropped to $566,169 in 2016.
“This is a nightmare,” said retired commercial urchin diver Jon Holcomb, 72, of Fort Bragg, who said he never witnessed such bad kelp conditions in his 37-year career. One of a handful of professional divers taking part in the urchin removal program, Holcomb created the urchin-sucking device they’re using based on an airlift, a tool used to clear sand and other small objects from the ocean floor. Rather than scuba gear, the divers use hookahs attached to small fishing boats for breathing and then dive down with the airlift. After scraping the urchins off the rocks, they suck the animals through the pipe and into a waiting net.
Each diver can clear around 1,500 square feet a day of urchin barrens, the vast areas of the sea floor that have been stripped of vegetation by the purple-spined creatures.
By having Holcomb and company remove urchin barrens from specific areas, starting with Caspar Cove near the town of Mendocino, Catton wants to see if they can create a few kelp “oases.” Bull kelp is an annual plant that depends on spores released by the previous year’s kelp to grow. The hope is that a few small thriving kelp forests could create enough spores to encourage growth elsewhere on the coast.
“We don’t know how many of those there will be, or how far the spores will travel,” she said.
The larger goal, Catton said, is to create a market for the purple urchins, which currently are not meaty enough to sell as seafood.
Gowan Batist of Fortunate Farm in Caspar, who already augments her soil with spent brewing grains from North Coast Brewing Co. in Fort Bragg, is advising the project organizers on how they could use sea urchins as a soil amendment. The shells offer a slow release of calcium, and just have to be thoroughly rinsed of salt water before being added to compost.
However, they will need to find a lot of farmers to use up all of the urchins they collect and to cover the substantial cost of collecting them. Meanwhile, the collected dead urchins sit on the dock, at Noyo Harbor in Fort Bragg, where staff and volunteers from the Noyo Center for Marine Science assess the catch.
Over Memorial Day weekend, Russo and the Watermen’s Alliance are planning a gathering at Ocean Cove on the Sonoma coast, a popular camping spot for Bay Area abalone divers. Instead of abalone this year, they’ll be diving for purple sea urchins. Russo sees it as a last-chance solution.
“The kelp is the bottom of the ecosystem,” he said. If the urchins “get rid of all the kelp, there’ll be no crabbing, there’ll be no salmon, there’ll be no nothing.”