MONTEREY — On a recent Saturday morning, scuba divers Keith Rootsaert and Dan Schwartz splashed into the ocean just east of Old Fisherman’s Wharf, the chilly water swallowing the sounds of Monterey Bay as they descended. Upon reaching the seabed, each diver grabbed a spiky purple sea urchin, braced it against a rock and pulverized its center with a welding hammer — all in the name of saving giant kelp.

The divers needed to ensure that the urchins were dead, but they didn’t have time to waste. Their goal was to kill hundreds of urchins apiece before the hourlong dive was over.

“Urchin culling” is an intervention — not a massacre. The intervention is necessary because the urchins are devouring the kelp, which Rootsaert describes as the marine equivalent of California’s redwood forests.

“If the redwood forests were on fire, people would be working tirelessly to save them,” Rootsaert said. “The kelp forests need saving, but because they are out of sight in the ocean it’s harder to get people to care.”

Rootsaert, a 57-year-old building systems engineer who lives in Monterey, founded the nonprofit Giant Giant Kelp Restoration Project in April 2021. Since then, he has taken more than 150 volunteers on more than 1,200 dives to cull more than 563,000 urchins.

Urchins are not an invasive species. The native creatures normally hide in crevices on the ocean floor and eat kelp that drifts down from the forest’s canopy. But a perfect storm of events beginning a decade ago threw the coastal marine ecosystem out of whack.

In 2013, a mysterious wasting disease wiped out the sunflower sea star, a voracious urchin predator with up to 24 limbs. From 2014 to 2016, the kelp forests languished through a persistent Pacific marine heat wave known as “The Blob.” Much of the kelp couldn’t take the heat. And without predators to keep them in check, the hungry urchins stormed out from their nooks and crannies and decimated the remaining kelp.

The event ravaged Pacific kelp forests from Mexico to Alaska. California’s North Coast lost 95% of its bull kelp forest. The Central Coast lost two-thirds of its giant kelp forest.

The Monterey Bay’s kelp forests used to support more than 1,000 marine species, including fish, snails, crabs and charismatic sea otters. But many of those species moved on when the urchins moved in.

Marine biologists call the desolate, urchin-filled areas “urchin barrens.”

“It’s like a moonscape where there once was a lush forest,” said Schwartz, 59, an Oakland resident who works in electronic security.

Rootsaert founded his kelp restoration project in the hopes of restoring the ecological balance.

Divers cull the urchins at a 100-meter square test site called Tanker’s Reef. A nearby site is left untouched so that scientists can compare results.

The experiment is a collaboration with environmental groups like Reef Check, which monitors the health of kelp forests along the West Coast, and government agencies such as the California Department of Fish and Wildlife and the Monterey Bay National Marine Sanctuary.

Rootsaert’s group relies wholly on volunteer scuba divers. “Volunteers are the best answer,” Rootsaert said. “You are building an effort that will sustain itself over time because you have people acting as ocean stewards.”

Volunteer Paul Souza, a 40-year-old licensed therapist from Fresno, started diving in Monterey Bay as a teenager in the late ’90s, which he describes as “the days of the infamous kelp crawl, where the kelp was so thick you’d have to crawl over it.” But when he returned in 2020, the kelp was gone and the urchins were in charge.

The divers say if the kelp forests go, so does the magic and diversity of the ocean. In addition, Rootsaert said, the local dive tourism, fishing and abalone farming industries would suffer.

Fish use kelp for spawning and protection from predators. Abalone eat it.

Rootsaert noted that kelp also protects shorelines by absorbing energy from big waves, in addition to absorbing 20 times more carbon dioxide than trees through photosynthesis. And all that carbon ends up on the ocean floor — as opposed to the atmosphere — as the kelp sinks to the bottom when it dies. So saving the kelp forests helps in the war against global warming.

“We’re fighting climate change with a hammer,” Rootsaert quipped.

Over the summer, Reef Check conducted surveys at the test site and reported exciting results: The urchin count is down, and the kelp count is up.

“I’ll be honest. I was skeptical,” said Dan Abbott, director of Reef Check’s kelp forest program. “But now we have really good evidence” of the project’s success.

The volunteer divers say they’re seeing the return of dozens of species. “Señoritas, rainbow perch and blue rockfish follow us around, waiting for us to smash an urchin so they can get a free meal,” Schwartz said.

Monterey Bay’s sea otters won’t touch urchins in the now desolate areas of the seafloor because they’re starving and devoid of nutritional value. But otters do eat urchins living near healthy kelp, acting as gardeners of sorts. And some otters have recently been observed foraging within the bounds of the test site where kelp has returned.

Still, some of the divers seem worried that there are tens of millions of urchins in the waters off the Monterey Peninsula and that there will never be enough divers to cull them all. Souza, for one, said he often feels he’s playing “whack-an-urchin.”

But the initial data from the test site is giving some scientists hope that it’s possible to clear enough urchins in key areas for kelp to get established. Once those patches of kelp forest are healthy, scientists say, the ecosystem has a better chance of restoring its balance.

Diver Gen Rohe, a 37-year-old marketing manager for an environmental nonprofit in San Francisco, sees the project as an opportunity for divers to help save the underwater world they love.

“We hear so much bad news about the environment,” she said. “With forest fires and climate change and all of these devastating stories, this project is a hopeful story. It’s gratifying to see our efforts pay off and witness the rebound of this beautiful ecosystem.”

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Fun urchin facts

• Sea urchins on the Pacific Ocean floor are the prey of otters and sea stars. But humans also eat them — their gonads to be exact — as a world-class sushi delicacy called uni.
• An urchin’s mouth is on its bottom side. Called “Aristotle’s lantern,”  it holds five teeth for chewing kelp.
• Urchins use special appendages called tube feet to snag blades of kelp, which they wrap around to their undersides and shove into their mouths. They also use the tube feet to walk and breathe.
• Urchins are nocturnal. They’re on the move at night to find food.
• Starving urchins can live for years without eating.

Source:  Monterey Bay Aquarium, Oceana

For more information about the Giant Giant Kelp Restoration Project, visit www.g2kr.com.