Evan Hou
Imagine looking out over the Pacific and seeing underwater forests swaying with the currents, teeming with life. For centuries, California’s kelp forests have been a foundation of marine biodiversity, sustaining fish, invertebrates, and marine mammals while stabilizing coastal ecosystems. These towering underwater canopies also play a crucial role in carbon sequestration and shoreline protection. However, in recent years, immense stretches of these forests have vanished, leaving behind barren seascapes dominated by unchecked sea urchins. The rapid decline of California’s kelp ecosystems is an ecological crisis with far-reaching consequences for marine life, local fisheries, and climate resilience.
What’s Happening to the Kelp?
Kelp forests are marine ecosystems composed of large brown algae, primarily Macrocystis pyrifera (giant kelp) and Nereocystis luetkeana (bull kelp). These towering algae attach to rocky substrates on the seafloor and grow toward the surface, forming dense canopies that shelter marine species and provide essential habitats. Much like terrestrial forests, kelp forests support complex food webs and contribute to coastal health by buffering wave energy and cycling nutrients. But in the past decade, Northern California has lost more than 95% of its kelp forests, leaving behind rocky seafloor stretches covered in purple sea urchins.
This ecological collapse was triggered by several environmental disruptions. In 2013, a massive marine heatwave, known as “the blob,” warmed coastal waters by up to seven degrees Fahrenheit, stressing bull kelp that relies on cold, nutrient-rich water. At the same time, an outbreak of sea star wasting syndrome wiped out the sunflower sea star, the kelp forest’s most important urchin predator. With no natural check on their population, purple sea urchins exploded in numbers—by over 10,000%—and began devouring every last trace of kelp.
Unlike other species, urchins don’t die when food becomes scarce. Instead, they enter a state of dormancy, carpeting the ocean floor in what scientists call “urchin barrens.” In these barren zones, new kelp spores struggle to take hold, making natural recovery nearly impossible.
Ecological and Economic Consequences
The loss of kelp forests has ripple effects that extend beyond marine ecosystems. These underwater forests once provided shelter and sustenance for an array of species, from fish and sea slugs to sea otters and seabirds. As the kelp disappears, so do these creatures, leading to biodiversity collapse. The economic impact has been just as severe—California’s once-thriving abalone industry has collapsed, and commercial red urchin fisheries have suffered as starving purple urchins outcompete them for food. Even coastal communities feel the impact, as kelp forests once shielded shorelines from erosion and storm surges. Without them, coastal areas face greater storm damage and rising infrastructure costs. In Northern California, places like San Rafael, Corte Madera, Bay Farm Island, and Foster City are sinking over 0.4 inches per year due to sediment compaction and erosion. This subsidence, combined with lost kelp forests, heightens vulnerability to sea-level rise, which could exceed 17 inches in low-lying areas by 2050.
Restoring Balance
Despite the devastation, scientists and conservationists are fighting to restore kelp forests through innovative and community-driven solutions. In Fort Bragg, divers are manually removing purple sea urchins to clear space for kelp to regrow, while researchers are experimenting with large mesh traps baited with kelp to speed up the process. Meanwhile, some scientists are exploring an alternative approach: urchin ranching. Since starving purple urchins contain little of the prized uni (their edible roe), efforts are underway to “fatten” them in controlled environments before selling them to seafood markets, turning ecological destruction into economic opportunity.
Meanwhile, near Eureka, a pilot kelp farm in Humboldt Bay is cultivating bull kelp in hopes of reintroducing it into the wild. Scientists are also working to preserve genetic diversity by building a kelp seed bank, ensuring that restoration efforts have a resilient foundation. At Friday Harbor Laboratories in Washington, researchers are breeding sunflower sea stars in captivity with the goal of reintroducing them into the wild, restoring a key predator that could help keep urchin populations in check.
A Future for Kelp
The decline of kelp forests is not just a regional issue—it’s a global challenge with far-reaching consequences. From the Pacific Northwest to Tasmania, kelp ecosystems are vanishing at an alarming rate, driven by warming waters, shifting predator-prey dynamics, and human activity. Yet, around the world, scientists, conservationists, and coastal communities are proving that recovery is possible. By managing urchin populations, cultivating resilient kelp strains, and restoring key predators, we can give these vital ecosystems a chance to rebound.
Kelp forests are more than just marine habitats—they are carbon sinks, coastal protectors, and biodiversity hotspots. Their survival is intertwined with the health of our oceans and the resilience of our planet. With dedicated action, innovation, and collaboration, these underwater forests can thrive once more, safeguarding marine life and coastal communities for generations to come.
Citations
Bindman, Ariana. “San Francisco Is Sinking, Scientists Say.” SFGATE, 11 Feb. 2025, www.sfgate.com/local/article/san-francisco-sinking-sea-level-rise-20161334.php. Accessed 15 Feb. 2025.
NOAA. “Kelp in Decline.” Greater Farallones National Marine Sanctuary, farallones.noaa.gov/eco/kelp/decline.html. Accessed 10 Feb. 2025.
NOAA. “Pioneering Project to Restore Bull Kelp Forests in Greater Farallones National Marine Sanctuary in California.” NOAA, 2024, www.fisheries.noaa.gov/feature-story/pioneering-project-restore-bull-kelp-forests-greater-farallones-national-marine. Accessed 10 Feb. 2025.
Rocchio, Laura. “Monitoring the Collapse of Kelp Forests.” NASA, NASA, earthobservatory.nasa.gov/images/148391/monitoring-the-collapse-of-kelp-forests. Accessed 10 Feb. 2025.
Zuckerman, Catherine. “The Vanishing Forest.” The Nature Conservancy, 26 May 2023, www.nature.org/en-us/magazine/magazine-articles/kelp-forest/. Accessed 10 Feb. 2025.