On a cold morning off the Mendocino County coast, a volunteer diver from Berkeley drops below the surface and lands on a reef that looks nothing like the lush underwater forests that once defined Northern California. The kelp is gone. In its place, a carpet of spiny purple sea urchins stretches in every direction. The diver gets to work, cracking urchins by hand and stuffing mesh bags until they are heavy enough to haul topside.
This scene has played out hundreds of times since the California Department of Fish and Wildlife and Reef Check California began organizing volunteer crews to physically remove purple urchins from targeted reef sites along the North Coast. Bay Area residents are among those suiting up for the effort, traveling north to places like Caspar Cove to join what amounts to an underwater landscaping project with ecological stakes.
By 2022, the partnership had pulled nearly 50,000 pounds of purple urchins from the ocean floor, according to the California Ocean Protection Council. Monitoring at treated sites showed bull kelp density climbing compared to untreated control areas, an early sign that clearing urchins can give kelp a chance to recolonize bare rock.
How the crisis started
The collapse traces back to around 2013 and 2014, when two disasters hit Northern California’s marine ecosystem almost simultaneously. Sea star wasting disease wiped out populations of sunflower sea stars, the primary predator keeping purple urchin numbers in check. At the same time, a prolonged marine heatwave, sometimes called “the Blob,” stressed bull kelp directly by warming the water beyond what the algae could tolerate.
With their main predator gone and ocean conditions working against kelp, purple urchin populations exploded. The animals devoured kelp faster than it could regrow, converting once-productive forests into what marine ecologists call “urchin barrens.” A peer-reviewed study published in Communications Biology found that more than 90% of bull kelp canopy vanished across some regions, with the damage stretching along roughly 350 kilometers of coastline. The researchers described a persistent regime shift: even after the heatwave ended, kelp did not bounce back because urchin densities remained too high for young plants to survive.
Sunflower sea stars, listed as critically endangered by the International Union for Conservation of Nature in 2020, have shown little sign of natural recovery along the California coast. Without that predator, there is no biological check on urchin grazing pressure, which is why human removal has become the primary tool.
What the removal work looks like
The process is simple in concept and grueling in practice. Volunteer and professional divers descend to urchin barrens, working in teams to either collect urchins into bags or crush them in place on the reef. Crews return to the same patches repeatedly because a single pass is not enough; urchins migrate in from surrounding areas, and any gap in effort can erase weeks of progress.
“You clear a patch of reef one weekend, and two weeks later the urchins have already started creeping back in from the edges,” said one Bay Area volunteer diver who has participated in multiple removal trips to Caspar Cove since the program began. “It is like mowing a lawn that never stops growing.”
To make this intensive removal legally possible, California regulators adjusted the rules. A CEQA project filing shows that the state extended a recreational bag limit exemption at Caspar Cove in Mendocino County, allowing divers to harvest urchins in quantities far beyond normal recreational limits. The exemption is tied specifically to kelp restoration and scientific data collection, effectively turning recreational divers into authorized participants in ecosystem recovery.
Some of the removed urchins are finding a second life on land. According to NOAA’s Office of National Marine Sanctuaries, urchins pulled from sanctuary restoration sites are being processed into compost. The program connects marine cleanup to agriculture, though it remains small-scale and no published data yet quantifies how much compost has been produced or which farms are using it.
It is worth noting that healthy purple urchins with full gonads can be sold as uni, a prized sushi ingredient. But urchins from barrens are typically starved and commercially worthless because they have already consumed all available food. That distinction matters: the animals being removed are not a lost harvest. They are ecological dead weight, too numerous and too hungry to support either a fishery or a forest.
Signs of progress and the limits of scale
The early monitoring results are genuinely encouraging. At sites where divers have maintained consistent urchin suppression, bull kelp has begun to reappear. Kelp fronds anchoring to cleared rock and growing toward the surface represent exactly the kind of recovery that scientists hoped targeted removal could trigger. The California Ocean Protection Council’s 2022 data showed measurable density gains at treated reefs compared to nearby untreated controls.
But the gap between localized success and coastwide recovery is enormous. The Communications Biology study documented urchin barrens spanning hundreds of kilometers. Volunteer crews, no matter how dedicated, can only work a handful of sites at a time. Each cove or reef patch requires repeated visits over months or years to keep urchin numbers low enough for kelp to establish. Scaling that effort to match the scope of the problem would require resources and coordination far beyond what current volunteer programs provide.
Updated monitoring data from state agencies has been limited since the 2022 press release. Whether the kelp gains at early restoration sites have held, expanded, or reversed is not confirmed in any publicly available report as of spring 2026. Kelp recovery depends on sustained pressure: if removal crews stop visiting a site, urchin populations can rebound within a single season and graze down new growth before it matures.
Researchers and agencies are also exploring complementary strategies. Captive breeding programs for sunflower sea stars are underway at facilities including the University of Washington’s Friday Harbor Laboratories, though reintroduction to the wild remains years away at best. Some scientists have proposed kelp aquaculture as a way to seed spores into cleared areas, accelerating regrowth. None of these approaches have reached operational scale along the Northern California coast.
Why Bay Area divers keep driving north
Kelp forests are not just underwater scenery. Along the Northern California coast, they serve as nursery habitat for rockfish, lingcod, and abalone, species that support both commercial fisheries and the regional food web. Kelp canopy buffers shorelines from wave energy, and the forests sequester carbon as they grow. The collapse of more than 90% of bull kelp canopy did not just change the look of the reef. It rippled through fisheries, tourism, and the broader coastal economy.
For Bay Area volunteers making the drive north to Mendocino, the work is a tangible way to push back against an ecological crisis that can otherwise feel abstract. Each bag of urchins hauled to the surface is a small, measurable act in a restoration effort that will likely take years to show whether it can hold ground against a problem that reshaped an entire coastline in less than a decade.
The honest read of the evidence, as of spring 2026, is that targeted urchin removal works at the scale of individual reefs but has not yet proven it can drive recovery across the full affected range. What the volunteers are doing is real, physically demanding, and producing documented results. Whether those results can outpace the urchins over the long term is a question that only sustained effort and continued monitoring will answer.
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*This article was researched with the help of AI, with human editors creating the final content.
