Early on a gray summer Saturday, an unusual assemblage — commercial fishermen, recreational boaters and neoprene-clad divers — gathered for a mission at Albion Cove, a three-hour drive north of San Francisco.
“Our target today is the purple urchin,” said Josh Russo, a recreational fishing advocate who organized the event. “The evil purple urchin.”
Five years ago, assigning wickedness to the purple urchin, a shellfish the size of a plum with 6-millimeter spikes, would have been absurd.
That was before the urchins destroyed Northern California’s kelp forests.
A warming ocean and a starfish die-off is leading the purple sea urchin to go on a kelp feeding frenzy. (Gabriella Angotti-Jones/The New York Times)
The underwater forests — huge, sprawling tangles of brown seaweed — are in many ways just as important to the oceans as trees are to the land. Like trees, they absorb carbon emissions and they provide critical habitat and food for a wide range of species. But when climate change helped trigger a 60-fold explosion of purple urchins off Northern California’s coast, the urchins went on a feeding frenzy and the kelp was devoured.
The dangers extend beyond this inlet: Kelp forests exist along the cooler coastlines of every continent but Antarctica.
“It would be like one of those beautiful deciduous forests turned into a desert,” said Gretchen Hofmann, a professor at the University of California, Santa Barbara. “But in the matter of five years.”
Already, Maine’s forests of sugar kelp have experienced declines. And in Tasmania, kelp forests have succumbed to a purple urchin outbreak. Here in Albion, they’re trying to avoid a similar fate.
The divers went to work, scraping purple urchins off the bottom of the cove, hoping it would allow the kelp, which has declined 93 percent in Northern California, to grow back.
The kelp’s disappearance is a story of an interwoven food system breaking down, and in the process threatening people’s livelihoods. Some of the first people to sound the alarm about the purple urchins were commercial red urchin harvesters, said Cynthia Catton, an environmental scientist with the California Department of Fish and Wildlife.
Red urchins are commercially viable because people eat them — or more specifically, their gonads. The delicacy is better known to sushi aficionados as uni. But the growing purple urchin population outcompeted the red urchins for kelp. Without kelp, the red urchins starved. That cut the value of Northern California’s commercial red urchin fishery from $3.6 million in 2013 to less than $600,000 in 2016.
The trouble began with the starfish. Sunflower starfish, whose appendages can span about a meter, normally eat purple urchins, helping to limit their numbers.
But in 2013, the starfish began dying. Today, there’s still no consensus as to why. But around the same time, a mass of warm water appeared hundreds of kilometers off Alaska, British Columbia, Washington State and Oregon. By 2014, that warm water had moved toward land, stretching from Southeastern Alaska down to Mexico.
Researchers and locals called it “the Blob.” It would last into 2016.
“Human-caused global warming made it much more likely to get as extreme as it did,” said Nathan Mantua, a physical scientist at the United States’ National Oceanic and Atmospheric Administration. Over 90 percent of the heat linked to greenhouse gases emitted by humans has been absorbed by the ocean, increasing its temperature.
The Blob also slowed the process of upwelling, in which cooler waters and nutrients move from deeper in the ocean up to the surface. That choked off a critical supply of nourishment for the kelp, which also prefers cooler waters.
In the absence of predators and food supplies, the purple urchins have gone on a rampage, said Mark Carr, a population ecologist at the University of California, Santa Cruz.
“They just line up like a horde of crazy individuals and storm across the reef, literally removing all algae,” he said.
The purple urchins will probably stick around.
“They’re like cockroaches of the ocean,” said Sonke Mastrup, a program manager at the California Department of Fish and Wildlife. “They can endure starvation conditions much longer than most of the other critters.”
In an attempt to bring back the kelp, Mr. Russo has raised more than $120,000 from grants and individual divers to organize culling events.
The goal, Dr. Catton said, is to create kelp oases: places where kelp can safely rebound, free from purple urchins.
“There’s a group of people who believe they can change the trajectory here of what is going on in nature,” Dr. Mastrup said. “I am hopeful but skeptical.”