Trapping Millions of ‘Zombie’ Urchins Could Restore California’s Once Mighty Kelp Forests

Grant Downie is cruising through Caspar Bay, a small cove 150 miles north of San Francisco on the rugged Mendocino County coast. From the helm of his 18-foot fishing boat, The Rose, Downie steers along the jagged cliffs that surround a pristine beach at the shore.

The sea in this protected inlet appears peaceful and calm. But below the surface, all is not well.

Down in the dark green water, hundreds of thousands of spiny purple sea urchins are scavenging the few remaining scraps of bull kelp, a leafy seaweed that once canopied California’s coastal waters from San Francisco to Oregon.

Kelp provides habitat for countless marine species and captures carbon from the water and the atmosphere. But scientists say climate change is threatening kelp forests around the globe. In the last five years around 95% of Northern California’s bull kelp canopy was devoured by an influx of hungry sea urchins, aided by a temporary spike in ocean temperatures.

“This was one of the first areas we saw the purps really taking over,” says Downie, a 33-year-old second-generation commercial urchin fisherman.

By “purps,” he means purple sea urchins. Of course, it could also be “perps,” as in perpetrators. These ping pong-ball sized critters sprout sharp, violet purple spines, in all directions, and have voracious appetites for kelp and other algae. (They’ve also been known to devour jelly fish and even bird carcasses.)

The Nature Conservancy, a science-based nonprofit, is studying different ways to remove purple sea urchins so kelp forests can rebound. (Peter Arcuni/KQED)

Downie kills the engine and we drift up to a buoy that’s connected by 20 feet of rope to a flat, hula hoop-shaped mesh trap. For two days, it’s been lying on the craggy ocean bottom, baited with strips of bull kelp, quietly attracting the purple urchins.

Kelp once thrived in places like Caspar Bay. Now, Downie says the ocean floor is lined with bare rock and purple urchins. “There are reefs where it’s like a carpet of purple urchin.”

He hoists up the line, yelping with pleasure as a mound of urchins spill onto the deck. Urchins on top of urchins, some weren’t even able to reach the kelp, but “were just on the trap because the kelp was there,” he says.

What’s left of the bull kelp is a ragged green mass, covered in bite marks.

“They hammered it,” Downie says, describing the amount of kelp eaten by the urchin as “insane.”

A quick count reveals the trap brought up more than 300 of the spiny invertebrates — a new personal record for Downie with a single trap.

The Collapse of a Forest

Downie’s trapping work is part of a research project spearheaded by The Nature Conservancy, a science-based nonprofit in search of solutions to pave the way for kelp’s recovery.

The collapse of California’s kelp forests is complicated, but goes something like this:

Around 2014, a warm water blob from the Pacific Northwest combined with an El Niño pulse from the south to create a large, prolonged ocean heat wave. Water temperatures spiked nearly 7 degrees Fahrenheit above average in spots along the West Coast. Kelp thrives in colder waters, which have more of the nutrients it needs to survive.

The hardy kelp may have recovered naturally after the heat wave passed. But a second ecological disaster, potentially related to the warm waters, struck. A disease killed most of the sea stars on the West Coast, including the 24-limbed, bicycle-wheel-sized sunflower star that feasts on purple sea urchins. Without these predators around, the urchin population swelled.

The urchins, typically concealed in protective, rocky crevasses where they patiently wait for fallen kelp leaves, came out of hiding and mowed down the forest, stalks and all. The state’s North Coast got hit the hardest. The kelp in Central and Southern California waters fared somewhat better because other predators there, like sea otters and lobsters, also eat urchins.

For kelp to rebound, scientists first need to figure out how to remove millions of urchins from California waters.

A pile of purple sea urchins collects on a underwater trap in Caspar Bay. (Colin McHugh)

“Let there be no question,” says Mark Carr, a UC Santa Cruz marine ecology professor not affiliated with the Nature Conservancy project, “these forests will not recover until urchin numbers have been reduced low enough and their behavior shifts back to remaining in cracks and crevices.”

A New Solution

Over the past few years, scientists and wildlife managers have begun testing different solutions for solving the purple urchin problem. One well-documented approach has been to deploy scuba divers to harvest urchins by hand-plucking them off reefs. But diving is expensive and potentially dangerous in strong currents or bad weather.

Urchin trapping has been proposed as a comparatively safe and cost-effective way to cull a ton of urchin and safeguard kelp’s recovery.

“We’ve got these cleared areas in the harbor where we want the kelp to grow back,” Downie says, “Let’s just set traps all around it so that when the urchins come, they’re going to be in the traps.”

Since no one’s ever tried using traps to catch urchins along the West Coast, the California Department of Fish and Wildlife granted the Nature Conservancy project a special permit to test out the method. Downie designed the traps himself: the flat-as-a-pancake version and another with collapsible walls.

Grant Downie rigs an urchin trap with bull kelp and a GoPro camera. A single trap can capture more than 300 purple sea urchins. (Peter Arcuni/KQED)

You might think so many urchins would be good news for an urchin fisherman. But Downie makes a living scuba diving for the larger and meatier red sea urchins, the kind you pay $8 a piece for at sushi bars.

Only a fraction of purple urchins grow big enough to eat. When they moved in, he says the red ones died or moved on.

“Since this whole disaster, I’m hardly making a quarter of what I used to,” Downie says.

The disappearance of kelp has crippled other marine ecosystems, like the rockfish and red abalone fisheries that were once staples of the Northern California coast.

“It’s not just hurting the urchin divers,” Downie says. “That was a huge income for so many people.”

In the wake of the ecological and economic collapse, Downie decided to use his knowledge of urchins to help scientists find a solution.

“I had heard about the trapping project and I said, ‘Hey, I think it should stay urchin-based,’’’ he says. “We’re not trappers per se, and this [contract] could have gone to a crabber or somebody like that. But our industry is in decline, we’re looking for help.”

The Nature Conservancy pays Downie for his work, and he now represents the North Coast region on a state commission.

Zombie Urchins Survive for Decades Without Eating

Without much kelp left to eat, most of the urchins Downie pulls from the water are starving.

“On the outside they look fine, on the inside they’re everything but fine,” says Tristin McHugh, an ecologist who directs the kelp recovery project for the Nature Conservancy.

But that doesn’t mean they’ll die-off naturally. These zombie urchins, as scientists call them, can survive for decades, biding their time until more kelp grows.

“There are some places in the world known to have them for 70-plus years in that state,” McHugh says. Which means it may be up to humans to tip the scales back in favor of kelp.

The inside of what scientists call a “zombie urchin.” Urchins can survive decades in this state. (Peter Arcuni/KQED)

Other methods scientists are exploring for urchin removal include reintroducing natural predators, like sea stars or sea otters. Researchers at the University of Washington have begun the first-ever captive breeding program for sunflower stars, which still haven’t bounced back in California since the disease wiped them out.

Each method has potential benefits and challenges, which include cost, safety, feasibility and regulatory hurdles, to name just a few.

While research shows that sea otters eat urchins along the Central Coast, helping maintain patches of healthy kelp forest, Mark Carr from UC Santa Cruz, says it’s unlikely they would go after the zombies that blanket large areas of ocean floor.

“The otters are not going to go out and waste their time and energy feeding on urchins that have very low nutritional value,” he says.

If it pans out, urchin trapping has the potential to do some heavy lifting for conservation, especially when diving isn’t practical.

“By using traps, you may be able to extend your season for getting into the water,” says James Ray, a kelp specialist with the California Department of Fish and Wildlife. “And you can target specific areas on a more constant basis.”

By creating strongholds for kelp along the coast, he says, the forest may be better equipped to withstand future threats.

But trapping has its limitations, too. Divers can swim right up to urchins, but dropping traps requires some guesswork. Trappers must hope that the urchins will be in expected locations. While trapping is less expensive than diving, it’s still costly and requires continual effort, whereas introducing predators may eventually sustain itself.

The Nature Conservancy’s kelp project director Tristin McHugh points out the spore packet on a healthy bull kelp frond in Caspar Bay. (Peter Arcuni/KQED)

Ray, who’s been collaborating with the Nature Conservancy’s kelp recovery research, says no one method will be the “silver bullet answer.” He says trapping and diving could potentially work together, in tandem with other methods, as wildlife managers try to scale up solutions from small patches to the entire coastline.

“Any solution,” he says, “is likely going to be a sort of a mosaic of smaller solutions that all work, ultimately, towards trying to increase resiliency in our kelp forest ecosystems.”

McHugh agrees with the kitchen sink approach.

“We almost want these very simple, singular solutions,” she says, “But the really key piece right now is figuring out how many different methods we can utilize and facilitate this shift back into a kelp forest.”

The Nature Conservancy currently donates the urchin carcasses to a company for composting. But McHugh says the long-term goal is to find a commercial market for the calcium-rich shells, like fertilizer or even road building materials, to help fund urchin removals on a larger scale.

“Someone needs to buy the urchin because we can’t necessarily rely on grant funds or philanthropic funds,” she says. “We need to figure out how we can utilize purple urchin, whether it’s for soil additives or for pavement or whatever it is.”

‘Golden Tendrils’ of Hope

While there hasn’t been significant recovery of bull kelp in Northern California since the marine heat wave, there is some reason for hope. Ocean temperatures have normalized, restoring nutrients to a level “that can sustain kelp growth and productivity,” Ray says.

While climate change increases the likelihood of warming events, kelp is known for its resiliency, replenishing itself every year from new spores and growing up to 2 feet a day. Along the North Coast, there have recently beens some preliminary reports of kelp beginning to reemerge in some areas.

Case in point: Back in Caspar Bay, McHugh kayaks close to the beach, where the sandy bottom prevents urchins from moving in. Surrounding her on all sides is a healthy canopy of bull kelp.

“Just these glorious golden tendrils of kelp just floating, creating this wonderful canopy that houses tons of marine life, turns over carbon for us, just does everything that you would possibly want a canopy forming species to do,” McHugh says, “It’s currently doing for us right now.”

She hasn’t seen kelp in this cove in years.

“You can actually see the spore packets on the blades of the kelp getting ready to drop,” she says.

A single packet holds millions of spores.

Once they reach the seafloor, McHugh says, “male and female will find each other and they’ll wait for the next opportune ocean conditions to start growing and begin their life cycle again.”

It’s a sign, she says, that if scientists can get rid of the urchins, California’s underwater forests will have a chance to return.

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