Coastlines & the West

Hitting Rock Bottom: The Disappearance of California’s Underwater Forests

Repeated heatwaves continue to destroy California’s kelp forests, crippling coastal economies, tribal resources, and a treasured ecosystem. Can they still be saved?

Rockfish shelter in a kelp forest on the Monterey Peninsula   Steve Lonhart/ NOAA MBNMS

By Benek Robertson

MONTEREY, CA — In a thick hooded wetsuit and scuba diving gear, Keith Roostaert plunges into the ocean off Monterey State Beach. Deflating his vest, he descends towards a grid the size of a football field marked out on the rocky seafloor. He swims to his designated location in the blue-grey murk, armed with a steel hammer and clipboard. Then, he starts methodically smashing the thousands of sea urchins that cling to the bottom.

Roostaert is working to restore California’s underwater forests, which have been decimated by climate-driven ocean heat waves. By coordinating the removal of thousands of sea urchins, he hopes to protect Monterey’s kelp forests, the wellspring of its marine ecosystems, against a warming future.

In the cold, nutrient-rich waters of the California Current, dense groves of tree-sized seaweeds have flourished for millennia. Kelp forests are rich, productive ecosystems. They sequester carbon, protect the coastline from powerful waves, and support local fishing and tourism.

A young Giant Kelp, Macrocystis pyrifera. This species grows in the waters of Southern and Central California.

A young Giant Kelp, Macrocystis pyrifera. This species grows in the waters of Southern and Central California.   Steve Lonhart / NOAA MBNMS

In the last decade, marine heatwaves have slammed the Pacific coast, turning lush forests into underwater deserts. In Northern California, the impacts have been severe: nearly 95% of kelp ecosystems were wiped out, shuttering fisheries and crippling an economy dependent on the region’s coastal seas. Coastal towns further south could be at risk.

This ecosystem collapse has a visible culprit: millions of fist-sized purple pincushions with an appetite for algae. Purple sea urchins — a native species — are voracious grazers of kelp, and they are usually kept in check by hungry starfish and sea otters. But in 2013, a mysterious disease spread through the west coast’s starfish, leading to a mass die-off. Southern sea otters were hunted to near-extinction by fur traders in the 18th and 19th centuries. Today, a growing otter population thrives on the Central Coast, but it remains far smaller than its original size.

Urchins dominate a rocky reef in Point Lobos State Marine Reserve.

Urchins dominate a rocky reef in Point Lobos State Marine Reserve.   Steve Lonhart / NOAA MBNMS

The decline of urchin predators is compounded by large-scale climate shifts. About 90% of Earth’s rising heat energy from the last 50 years has accumulated in the ocean. A record-breaking marine heat wave rippled across the kelp beds from 2013 to 2015, causing temperature spikes that peaked at almost 7 degrees Celsius above normal. Warm, nutrient-deficient waters hindered the forest’s growth, all while urchins multiplied rapidly. Massive kelp declines followed, leaving scientists, conservationists, and stakeholders scrambling for solutions.

“So, basically we’re trying to build an army,” said Roostaert. He is training volunteer divers for a three-year effort to clear urchins from a patch of Monterey seafloor, in hopes of spurring kelp growth. In December, Keith obtained approval from state fisheries regulators to restore the kelp forest at Tankers Reef, a patch of shallow shale rock that has been overrun by sea urchins. Scientists from California Department of Fish and Wildlife, Monterey Bay National Marine Sanctuary, and Reef Check — a citizen science organization — will monitor the surrounding ecosystem. Starting in April, Roostaert will direct volunteer divers as they crush urchins across acres of seafloor, one square meter at a time.

Roostaert (center) and a team of Reef Check divers, ready to enter the water.

Roostaert (center) and a team of Reef Check divers, ready to enter the water.   Isabelle Groc

A targeted site for urchin removal in Pacific Grove Gardens Marine Conservation Area.

A targeted site for urchin removal in Pacific Grove Gardens Marine Conservation Area.   Giant Giant Kelp Restoration Project

Healthy kelp forests play a vital role in supporting productive fisheries, and Roostaert is concerned that Monterey’s catches are showing signs of decline. The region’s fisheries community, already suffering economically from the Covid-19 pandemic, has been impacted by restrictions due to crashing fish stocks. The region’s sardine fishery — once the lifeblood of Monterey’s Cannery Row — has nearly ground to a halt. Species such as rockfish and squid could be impacted as well. In a video assembled by local kelp advocates, local squid fisherman J.D refers to the kelp forest as “a nursery” that supports baby squid and other juvenile fish species.

Monterey Bay is still better off than California’s north coast. Mass kelp death in Northern California led to a federal declaration of commercial fishery failure for red sea urchin divers — the larger, more prized urchin species has been outcompeted by its purple counterpart. This was accompanied in 2018 by the closure of the recreational red abalone fishery, California’s last remaining abalone fishery. As sea urchins chew through the kelp, these oversized marine snails are starving.

On the North Coast, Diminishing Kelp Cover is a Warning Sign

The state of California conducts regular aerial photographic surveys of the kelp canopy off of rocky coastlines. According to state surveys and closer study by researchers at UC Davis and the state Department of Fish and Wildlife, kelp cover has declined drastically along the state’s northern coast. The map below shows the statewide picture over four separate survey years, and close-ups of four key locations.

Graphic: Map of kelp survey showing declining kelp cover in selected Northern California coastal areas.

Sources: Laura Rogers-Bennett, UC Davis; C. A. Catton, California Department of Fish and Wildlife; California Department of Fish and Wildlife (aerial surveys); ESRI (satellite imagery);

Geoff McGhee/Bill Lane Center for the American West

An abalone</a> on the California seafloor, with purple sea urchins in the background.” /></p>
<p><span class=An abalone on the California seafloor, with purple sea urchins in the background.   Athena Maguire/California Department of Fish and Wildlife

California’s abalone — a critical food source and cultural resource for coastal tribes — are in stark decline. For the Chumash tribe of Central California and many others, these shellfish are critical to cuisine, culture, and ceremony. Now, climate change, ecosystem collapse, and poaching have all but wiped out the abalone. The loss of kelp ecosystems is devastating; in the words of Leah Mata, a Northern Chumash artist who spoke to High Country News in 2018, “Western culture has taken our cultural resources for themselves.”

On the shores of Mendocino County, projects similar to Roostaert’s are already underway. Last year, policymakers, scientists and fisherman joined forces in a project at Noyo Bay, near Fort Bragg. A team of out-of-work commercial red sea urchin divers will clear purple urchins from 10 acres of seafloor. Scientists with the NGO Reef Check California collect data from the project, which is funded by the California Ocean Protection Council.

“We look forward to determining whether creating small kelp refugia along the North Coast might help to accelerate recovery more broadly across the region,” said Dr. Mark Gold, OPC’s Executive Director in a 2020 press release. This partnership has seen early success; divers documented kelp growth in recently cleared portions of the cove.

Using kelp oases to safeguard specific regions may prove effective, but bringing back collapsed ecosystems is a daunting task. The scale of this problem is immense, as urchin populations have exploded by more than 10,000 percent. Hundreds of millions of purple urchins now cling to the rocks off the California coast. In regions such as Tasmania, South Africa, and Japan, kelp forests that turn into urchin barrens have not recovered for decades. “[Urchins] are a very hardy species… and so they have the capacity to persist, even without suitable resources for them to feed on,” said Steve Lonhart, a marine ecologist at Monterey Bay National Marine Sanctuary. In barrens, the legions of famished urchins become emaciated, severely limiting their food value. Nevertheless, they keep clinging to the rocks, alive and ready to eat any kelp that tries to grow.

Some scientists are more optimistic about the kelp forests of Central and Southern California. “On the Central and South Coast, kelp resiliency does not seem to be as depleted as up north.” said James Ray of California Fish and Wildlife. Aided by the appetites of sea otters and other urchin predators, many stretches of kelp remain strong.

Monterey’s rocky seas are a patchwork of urchin barrens and healthy forests. So far, much of the kelp that remains is still healthy. “If you're able to maintain those patches of forest through predators like sea otters, that provides a really good base for kelp to recover and persist.” said Josh Smith, a PhD researcher at the UCSC’s Carr-Raimondi Lab.

Southern sea otters live in kelp forests, where they eat a variety of marine invertebrates, including urchins.

Southern sea otters live in kelp forests, where they eat a variety of marine invertebrates, including urchins.   Steve Lonhart / NOAA MBNMS

A patch of kelp near Carmel, CA is surrounded by urchins.

A patch of kelp near Carmel, CA is surrounded by urchins.   Steve Lonhart / NOAA MBNMS

“We’re trying to hang on to all of the old growth kelp that we can preserve, so that if the urchins should die off and conditions do change, we’ve got a chance,” said Roostaert. His restoration project begins in April, but only time will tell if his work can save Monterey’s kelp ecosystems — and the communities who depend on them — from a warming future.


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Edited by Felicity Barringer.


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Felicity Barringer

Lead writer

A national environmental correspondent during the last decade of her 28 years at The New York Times, Felicity provided an in-depth look at the adoption of AB 32, California’s landmark climate-change bill after covering state’s carbon reduction policies. MORE »

Geoff McGhee

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Geoff McGhee specializes in interactive data visualization and multimedia storytelling. He is a veteran of the multimedia and infographics staffs at The New York Times, Le Monde and MORE »

Xavier Martinez

Xavier Martinez

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Xavier graduated from Stanford in 2023 with a degree in economics and is currently a master’s student in Stanford’s journalism program. He has written about the high phone call costs faced by U.S. inmates, temporary Mexican workers’ interactions with the labor market and the efficacy of government healthcare assistance programs. A lifelong lover of charts and maps, he enjoys combining data journalism with narrative-style reporting. 

‘& the West’ is published by the Bill Lane Center for the American West at Stanford University, which is dedicated to research, teaching, and journalism about the past, present, and future of the North American West.

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