Divers say that the ocean changes completely when you go below the surface off the coast of California. The noise goes away. The light changes. It looks more like a cathedral than an ecosystem if you’re swimming through a healthy kelp forest. The long amber stalks rise at least 100 feet from the seafloor, the leafy blades spread out at the surface, and light falls through them in thin, shimmering columns. Someone who lives in Santa Cruz and works as an oceanographer for the U.S. Geological Survey has called it “beautiful, like its own little universe.” It is a universe that is going away.
Along the North Coast of California, kelp forests that used to go on for miles have been cut down by more than 95% since the middle of the 2010s. That number comes from McPherson’s own research, which was published in 2021 in Communications Biology. It used images from 34 years of satellites to show how canopy coverage changed over time. They are so stark that it takes a moment for them to sink in. It’s not 20%. Not half. Over 95% of them are gone in about five years.
Around 2014, there was a heat wave in the ocean that made scientists very worried. This was the start of the collapse. But the timing was what made it so terrible. Before the warm water got there, a disease that makes people lose weight had spread through the sunflower sea stars. These sea stars are important for keeping the number of sea urchins in check. Since there were no more sea stars and the water was too warm for kelp to grow, urchins grew and ate what was left of the forests. McPherson says that the ecosystem had always been strong, able to recover from storms, temperature changes, and other problems. It couldn’t do it this time. “It led to the complete collapse of the ecosystem,” she has said, “and it still has not recovered.”
What we might have missed in all of this is how much those forests did that we didn’t even notice. Coral is not kelp. Tropical reefs are the subject of conservation posters and documentaries, but this one isn’t. Most people, including most policymakers, have only a vague idea that it’s there. Aaron Eger, a marine biologist at the University of New South Wales, says that about 750 million people live within 30 miles of a kelp forest. This includes people who live in cities like Los Angeles, Sydney, and Cape Town. They always get something good from these ecosystems, and it’s free for them.
The study by Eger and 18 others tried to put a price on some of these benefits and came out in 2023 in Nature Communications. They came up with an average annual value of $500 billion by looking at things like commercial fishing, nutrient absorption, and carbon sequestration. They pointed out that number didn’t even include protect against storms along the coast or ocean tourism. It’s possible that the real number is a lot higher. It’s also a number that makes California’s loss seem less like an environmental story and more like an economic one.
More attention should be paid to the carbon question in particular. Kelp can grow up to two feet a day if the conditions are right. This is a very fast rate of growth. That growth turns carbon in the air into biomass at a rate that some researchers say is 20 times faster per acre than forests on land. Some of that carbon sinks into the deep ocean when storms and currents carry kelp pieces out to sea. There, it can stay locked away for hundreds of years. So, the loss of alive kelp forests along the coast of California is more than just bad for the environment. It means that the oceans can’t clean up the mess we’ve made in the atmosphere as well.
From what I’ve seen, kelp forests have kind of been invisible—they look normal from the outside, most people don’t know what they are, and they’re too deep underwater to make people care about them the way coral reefs or Amazon deforestation have. For years, the scientists who study these places have been making the case that they are important, even though the places have been slowly falling apart. It’s still not clear if efforts to fix things can undo the damage on a meaningful level. It is clear that the ocean’s ability to take in carbon is not something that stays the same around the world. Part of it depends on a bunch of brown algae moving around on the ocean floor off the coast of California. There’s not nearly as much of it as there used to be.
