If you have ever watched the sunset from Santa Monica Pier, you have a stake in what happens below the surface. In recent years, a volunteer-driven campaign coordinated by The Bay Foundation removed approximately 5.8 to 6 million purple sea urchins from nearshore waters in Santa Monica Bay. The goal was simple and bold: clear space for kelp to return and restore an underwater forest that supports wildlife and protects the coast. Trained scuba divers logged more than 15,000 hours to make it happen, often in cold water with heavy gear. Within about three months of reducing urchin pressure, towering fronds of kelp began to rise again.
Santa Monica Bay’s underwater forests matter
Kelp forests are the beating heart of California’s coastal ecology. Picture long, light-filled corridors that stretch toward the surface and sway with the swell, creating habitat for fish, crabs, sea stars, and lobsters. This vertical structure shelters juvenile fish, feeds countless invertebrates, and draws predators that knit the food web together. The canopy also dampens wave energy and storm surge, which helps buffer beaches and bluffs during rough weather. For a region that thrives on recreation and tourism, healthy kelp forests mean richer dives, better fishing, and a more resilient shoreline.
How a sea urchin boom created barren seafloor
The crisis began when purple spiny sea urchins exploded in number and turned lush forest into rock-scoured barrens. Natural checks and balances had eroded. Historic fur hunting removed sea otters, a major urchin predator, and a more recent sea star die-off further reduced predation pressure. The result was a seafloor dominated by starving, densely packed urchins that grazed away every new kelp sprout. In hotspots, densities reached dozens per square meter, which kept the ecosystem locked in a degraded state.
Why culling a native species made ecological sense
Culling a native animal can sound counterintuitive, yet the urchin boom was not a stable or natural equilibrium. It reflected a collapse in predators and a broken feedback loop that trapped the system in a barren phase. The Bay Foundation’s team focused on resetting the balance so kelp could re-establish and predator-prey dynamics could normalize. Divers targeted overabundant, emaciated urchins that were blocking recovery while leaving larger, marketable individuals that support local fisheries. The intent was not to eliminate urchins, but to reduce grazing pressure to a level the ecosystem could sustain.
Hand tools, cold water, and a massive volunteer effort
The method was simple and hands-on. Teams descended with hammers, cleared open rock, and reached into crevices to extract urchins that would otherwise survive and repopulate the area. Volunteers put in more than 15,000 dive hours, often working up to nine hour shifts that demanded careful focus and steady endurance. The physical toll was real, with repetitive motions and long cold dives becoming the routine. By the end of the push, roughly six million urchins had been removed, and the cleared habitat covered an area comparable to more than 60 football fields.
Kelp’s rapid comeback and the return of wildlife
Kelp is a natural sprinter. Once the urchin wall thinned, blades began to appear within about three months, leveraging the plant’s ability to grow several feet per day and reach heights near 100 feet. As canopy formed, the underwater forest regained its complexity, which drew back a wider array of species. California spiny lobsters became easier to spot as crevices and vertical structure returned. The revived kelp also dampened wave energy again, a service that helps protect coastal infrastructure during storm seasons.
Divers’ perspective from the seafloor
For the volunteers, the work felt both gritty and inspiring. Many described the long hours of hammering as exhausting, yet they also shared how it felt to glide through sunlit kelp corridors that had been empty just weeks earlier. Seeing young blades attach, stretch upward, and sway with schooling fish offered instant proof that their efforts mattered. That tangible progress helped keep teams motivated through the most demanding days. It also turned a technical restoration plan into a personal mission for many involved.
What this project teaches other coasts
The lesson from Santa Monica Bay is pragmatic and hopeful. Conservation does not always require complex technology or decades of waiting. Targeted, science-guided actions can unlock rapid recovery, even when the steps feel unconventional. Community-led restoration, backed by clear selectivity and careful monitoring, can reset systems that have slipped into persistent decline. The approach offers a template for urchin barrens elsewhere: reduce grazing pressure, allow kelp to re-establish, and create space for predators to rebound.
What comes next for Santa Monica’s kelp
The Bay Foundation and partners are continuing to track kelp persistence and urchin numbers to keep the system balanced. Future work could scale citizen-diver programs to other stretches of the California coast that face similar pressures. Long-term recovery also depends on broader marine conservation, including support for predator return and disease monitoring for keystone species. With continued vigilance and community involvement, the forests that shelter marine life and protect the shore can keep growing. For anyone who loves this coastline, that is welcome news you can see in the water.