At a summer lunch at Harbor House, an inn with a two-Michelin-starred restaurant in the seaside town of Elk, California, chef Matthew Kammerer treated diners to a feast of creamy, umami-rich purple urchin and a lot of words you’ve probably never heard of.

He draped golden lobes of uni, the culinary name for the sea urchin’s gonads, over yuzu chawanmushi and blended them into mayo for fried maitakes. He doused roasted cabbages with urchin sauce and even candied the seafood to serve atop seaweed ice cream.

It was the launch of the nation’s first Urchin Fest, and Kammerer had designed his menu, he says, “to show that this thing is delicious.” The two-day festival was meant to whet the public’s appetite for a spiny invertebrate whose exploding population, with its hunger for kelp, threatens the life of the seas and the livelihood of humans along the Mendocino coast.

At Urchin Fest, chef Matthew Kammerer’s dishes included candied uni, served atop atop seaweed ice cream. The idea, he said, was “to show that this thing is delicious.”

Kelp is in similar trouble in oceans around the world, as the effects of climate change—warming seas, extreme weather, predator loss—throw the eco-system out of alignment. For human safety and livelihood, that’s bad news. Kelp buffers shorelines, protecting coastal communities from storm surges. It can store up to 20 times more carbon than land forest. And it provides habitat for the seafood we eat.

Boiled Kelp, Anyone?

Just past the shoreline of this Northern California county, the Pacific Ocean was once home to a thriving eco-system of bull kelp up to 43 yards high. Fourteen years ago, when he was first harvesting red urchins, the purple ones’ bigger cousins, commercial diver Grant Downie says he would swim “through kelp so thick, you could barely make it through.”

The kelp forest supported an abundance of life. “Red urchins and abalone hung in a feed line,” he says. “Gopher cod and lingcod were all over the bottom in hiding places. Looking upwards to the canopy, you’d see huge schools of black and blue rockfish circling, and it was not uncommon to see a massive sunflower star making its way around.”

Today? “It looks like a wildfire went through,” he says.

Tethered to an air hose, with a rake in hand and inner tubes for kneepads to protect his limbs from spines, Downie once harvested around 1,200 pounds of red urchins a day. Processors in Mendocino’s harbor towns boxed the catch for export, and, all in all, hundreds of residents made their living off of red urchins.

Then, in 2014, disaster struck. An El Niño supercharged by climate change heated a roving plume of water that boiled kelp in its wake. Then a separate pandemic spread in the warming water that ravaged the sunflower star—a sea creature up to a yard wide and with up to 24 arms. A lightning-quick hunter, the sunflower star was Mendocino’s primary remaining predator of the purple urchin. Six billion of them—more than 90 percent of the sunflower star’s global population—perished.

Purple urchins were left to broadcast spawn in the Pacific, proliferating by 10,000 percent and munching unfettered on their favorite food, bull kelp. They were finishing the job that warming seas had started. Eight years later, roughly 96 percent of the kelp, and many species that thrived amid it, including red urchins, are gone.

But the purples remain. They cover sea rocks in lavender spikes, creating desert-like seascapes called “urchin barrens.” Without kelp, the urchins are starving, but no matter. Gnawing on sea rock with its drill-chuck mouth, a purple urchin can live as a near-empty shell for 100 years. They’ve been likened to zombies.

Priceless Gonads

For its coastline and economy, Mendocino needs its kelp back. Fort Bragg’s Noyo Center for Marine Science is partnering with local divers and organizations such as the Nature Conservancy on interventions, including smashing and clearing urchin barrens. Marine labs are trying bull-kelp farming and incubating sunflower stars. Kammerer’s solution? Eat the zombies.

In Norway, a diver removes urchins to restore the kelp forests.

“It’s so human to find someone else to blame, but we did this,” he says. Now he serves diners exquisite purple-urchin dishes as often as he can, but other area chefs had essentially ignored the animal. So Kammerer helped organize Urchin Fest to bring uni-lovers to Mendocino and encourage his peers to feed them. “If the consumer isn’t interested in it, there will be no market,” he says.

For a sake-and-urchin pairing, Kammerer’s fellow organizers, Little River Inn’s Marc and Cally Dym, stuffed mochi-rice balls with an uni velouté for a mash-up of arancini and onogiri he called “unicini.” At Elk Cove Inn, where he whipped up pain perdu with celeriac, caviar, and uni cream sauce, chef Victor Passalacqua declared the purple urchins better than the red. “They’re sweet and more delicate,” he said.

“It’s so human to find someone else to blame, but we did this.”

One problem that manifested during Urchin Fest was that purple urchins spawn in spring, when the luscious stuff in their shells liquifies, coursing through the ocean to fertilize. Stress, including from harvesting, can put purple urchins in a spawning frenzy, too, their priceless gonads dribbling out. “So even though there’s millions of them, finding good-enough quality to serve was difficult,” says Kammerer.

That’s where another solution came in. Founded by entrepreneur Brian Tsuyoshi Takeda to help restore Japanese kelp forests and fisheries after the 2011 tsunami, Urchinomics is a top urchin-ranching operation. The company pays fishermen to harvest purple urchins and transport them to an aquaculture facility, where they fatten on kelp pellets made from the leftovers of nori production. Up to 12 weeks later, when their shells are full, the urchins are sold to restaurants.

Now, as the effects of some of these interventions have begun to manifest, Grant Downie is watching the ocean’s slow recovery in the location where the Noyo Center paid him to remove purple urchins.

“I saw bull kelp popping up as tall as four to six feet tall,” he says. One day, those urchins he gathers may be ranched on Mendocino’s bluffs, uni might be a staple at all the local restaurants, and the kelp forest will live again. At least that’s the hope.

Betsy Andrews is a Brooklyn-based journalist, editor, and poet. She contributes to Travel + Leisure, Food & Wine, and The Wall Street Journal