Hope grows for kelp forest recovery after volunteers smash 750,000 “zombie” urchins
They’ve been compared to cockroaches, zombies, and tribbles. Since 2015, millions of purple urchins have ravished California’s kelp forests. But now, volunteers braving treacherous swells, sharks, and frigid water have shown that kelp will come back if you cull enough urchins.
At Tankers Reef in Monterey Bay, the organization Giant Giant Kelp Restoration Project culled over 750,000 urchins in two years, allowing kelp forest to regrow. From 2021 to 2023, several hundred volunteer “urchinators” spent over 1,500 hours culling on a special arrangement with the California Department of Fish and Wildlife. Divers smashed urchins at a rate of 20-25 per minute.
“It’s going to be a continuous battle where we see just armies of urchins returning,” said Annie Bauer-Civiello with Reef Check, an organization that engages volunteers worldwide to monitor reefs. “They are like cockroaches; they can survive almost anything; they can live forever without food; and they have [almost] no gonads.”
The urchins are so unhealthy and lacking nutritious uni (gonads) that even their top predator, sea otters, have lost a taste for them in Monterey Bay. This is where volunteer divers come into play.
Kelp regrew at Tankers Reef, and with it came the diving seabirds, sea lions, seals, rockfish, and octopuses that call kelp forests home. Kelp counted by Reef Check more than doubled over the two-year period.
Fishing for solutions
These results have organizations across the state, including spear and abalone fishing groups, tribes, and universities hopeful and eager to implement solutions further up the coast.
“We’re asking now, ‘What more do we need to do?’” said Bauer-Civiello.
Culling urchins is part of a three-pronged approach that should also include reintroducing apex predators like the sunflower sea star and finding ways to boost kelp spawning and growth in places where it was once abundant, said Tristin McHugh, Kelp Project Director at The Nature Conservancy.
“We’re looking at restabilizing the entire kelp forest ecosystem,” McHugh said. “These studies are helping us understand all the tools in our toolkit for an overall kelp restoration plan.”
The California Ocean Protection Council funded $617,000 to cull urchins at Albion Cove and Noyo Harbor from 2020-2022 as part of a study on the effectiveness of urchin removal. Six vessels were deployed, five with hand crews and one with a vacuum. Bull kelp recovered after culling but it wasn’t sustained.
A Ten-Year Spread of Urchin Barrens
Vast acres of underwater desert, called urchin barrens, have spread up the California coast in the past ten years. Iconic kelp forests have disappeared across hundreds of miles. Abalone are also starving, since they only eat kelp. Divers often find empty abalone shells laying across the ocean floor.
The original culprit was “the blob,” a huge body of warm water that lingered at the Northern California coast over the winter of 2015 and 2016. It caused the purple urchins’ main predator north of Monterey Bay, the California sunflower sea star, to become vulnerable to a wasting disease. Within a few years, sea stars were locally extinct, and purple sea urchins exploded. Soon, much of the bull kelp was gone.
Bull kelp naturally die back each season and it’s unknown how many spores are left in the environment after ten years of decline.
“At Noyo, we didn’t see a massive recovery,” McHugh said, “so the next line of questioning is focusing on doing the kelp enhancement, too.”
Much to the disappointment of the divers at Monterey Bay, their unlimited culling allowance (technically a sportfishing amendment) was not renewed at the February meeting of the Fish and Game Commission. The state wants to watch whether the ecosystem can recover on its own now that the reef reached an ideal number of urchins (two per square meters) .
At Caspar Cove, the state is still allowing unlimited harvesting , and a volunteer diving group, Watermen’s Alliance, sets out monthly, rain or shine.
“It’s hard diving Northern California,” said Bauer-Civiello. “You have to do it in really cold water, incredible storms and swells, and with sharks nearby. It’s a remote, treacherous setting that makes it so hard to work in. It’s all the more admirable of all the people going up doing all that work.”
Hope on the horizon
Volunteer and commercial culling has shown that kelp forest can bounce back when urchins are culled. Biologists have succeeded at spreading spores from lab-grown kelp in Albion Bay. Scientists have successfully bred sunflower sea stars. And, commercial divers have started spotting wild sunflower sea stars again.
“We’re hitting the ten-year mark of when this massive loss of kelp began. But there’s so many bright, talented minds working on this,” said McHugh with The Nature Conservancy. “People all over the world are navigating this with us. What worked elsewhere and what can we bring home that will work, not only ecologically, but socially?”
Even one strand of kelp regrowing in a place that was once an urchin barren brings a smile to Bauer-Civiello with Reef Check.
“To me, that’s super exciting and it makes me hopeful. It’s like this little rainbow. You have to imagine that we’re marching uphill in the snow with the wind, and here’s this little flower. It is hope to us.”
Collaborators on these kelp forest studies include:
Reef Check
The Nature Conservancy
Moss Landing Marine Laboratories (San Jose State Marine Lab)
Sonoma State University
California Department of Fish & Wildlife
California Ocean Protection Council
Learn more about bull kelp and urchin barrens:
Video: The Forest Beneath the Sea
Bull Kelp
Video: Urchin Barrens
Article: The Vanishing Forest
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