The ocean’s most important carbon capture system is under threat

ANACAPA ISLAND, Calif. - Frank Hurd gently parted the curtains of giant kelp that reached upward through the cold waters of the North Pacific, looking for signs of life.

Kelp forests cover a quarter of the world’s coastlines, stretching from Antarctica to Australia, Mexico to Alaska, providing food and shelter for thousands of species, while sucking carbon from the atmosphere. But over the past decade, thanks to warming waters and overfishing, they’re disappearing.

On this afternoon, Hurd, a marine biologist at the Nature Conservancy, said he was relieved to find thick kelp canopies surrounding an unpolluted patch off Anacapa Island, part of the Channel Islands National Park in California. But, he says, such refuges are becoming harder to find. “The scale of this problem is dire,” Hurd said.

The fate of the world’s kelp forests may depend on controlling its sworn enemy - sea urchins - and the Nature Conservancy, an Arlington-based environmental group, says it has a plan. It is touting urchins as a culinary cuisine, hoping to appeal to commercial fishermen who could scoop them out of the ocean. It is also attempting to increase the population of their natural predators, sea stars and growing kelp in controlled environments before releasing the algae back into the sea.

“There really is no single silver bullet option to solve this problem. We need to invest in comprehensive solutions to reestablish healthy, resilient ecosystems,” Hurd said.

Kelp are essentially the ocean’s equivalent of trees. They absorb carbon dioxide and nitrogen compounds, helping clean the atmosphere while capturing up to 20 times more carbon per acre than land forests. They also provide a vital habitat for a broad range of marine life; without them, entire ocean ecosystems would crumble.

But the size of kelp forests off the coast of Northern California has shrunk by more than 95 percent since 2014, according to satellite data analyzed by the Nature Conservancy. Other regions have had similar losses: Tasmania’s canopies have decreased by 95 percent, as have Chile’s. Globally, kelp forests along coastlines have declined by a third over the past decade, according to a paper published in the American Institute of Biological Sciences journal BioScience.

“There’s been a catastrophic loss,” said Tom Dempsey, the Nature Conservancy’s California Oceans Program director. “And it’s been all but completely ignored.”

The problem was exacerbated along the California coast by a 2013 heat wave. The average kelp canopy cover off the coasts of Mendocino and Sonoma counties in Northern California fell from 2 million square meters to 60,000 square meters over the course of two years, according to the Nature Conservancy. This marine heat wave, known as “the Blob,” along with a fast-spreading marine virus, all but wiped out the sunflower sea star, the main predator of urchins.

“It’s like this endless parking lot, stretching for miles in every direction, covered in purple urchins,” Dempsey said. With few starfish, the urchin population “exploded to up to 100 times their previous numbers.”

The Nature Conservancy began looking for ways to get the urchin population under control in 2018. Traditionally, efforts to cull the spread of urchins - the purple, rather than the marketable red or green species - consisted of volunteer divers swimming out to sea and smashing the spiky echinoderms with a hammer.

But that would take too long, they decided, and the group began testing some alternatives.

First, they hoped to increase commercial demand for sea urchins, noting that their shells contain calcium carbonate that could be made into fertilizer or be used in cosmetics. They also hoped to popularize uni, the reproductive organs of the urchins, as a restaurant cuisine. But the type typically considered a cuisine are not the invasive purple variety that eat at the roots of kelp.

“Purple urchin is definitely the less desired species in the seafood market,” Dempsey added.

The organization is also trying to find ways to revive the sea urchins’ predator - the sea star. The sea star population has fallen victim to warming waters too, allowing the urchin population to skyrocket.

“Sea stars are sorely missed in our near-shore environment, and having them back is critical,” said Scott Groth, head of the marine resources program at Oregon’s Department of Fish and Wildlife, which has reported a sharp decline in sea stars.

In 2019, the Nature Conservancy’s team collected 28 adult sea stars to create a “breeding colony.” One sea star was nicknamed after Vincent Van Gogh because its pattern was similar to the artist’s paintings, while another was named after Prince because of its purple arms.

But the first effort largely flopped. The team didn’t know what to feed the juvenile starfish or even what type of water they thrived in.

This year, the Nature Conservancy says it is raising another batch, which has already produced thousands of juvenile starfish. This time they separated individual starfish by size to keep cannibalism at a minimum and crushed individual baby bivalves, including tiny clams and oysters, for the juvenile starfish to eat.

“We tried out all sorts of possible foods, container types, flow designs, water change frequency, levels of filtration, numbers of juveniles per container etc.,” Jason Hodin, marine larvaologist at the University of Washington, said. “Now we’ve figured things out, we’re hoping to scale this up as much as we can.”

But even that may not be enough. Hundreds of thousands of sea stars would be needed across the California coast to make a dent in the tens of millions of sea urchins decimating the kelp.

To aid their efforts, the Nature Conservancy launched an experimental kelp farm in April with GreenWave, an organization that specializes in regenerative ocean farming. They are growing kelp in industrial tanks and then plan to transfer them into the Pacific Ocean once ready.

The group hopes that strategically placed kelp farms will be encouraged to connect with wild kelp patches through spore dispersal, Dempsey said.

“Essentially, like filling in a chessboard,” he said. But, he added: “It’s going to take time, and a lot of funding.”

Unfortunately - for the kelp forests, and the countless species that rely on them - both time and funding are in short supply.