PC: Steve Lonhart/NOAA
Since 2023, urchins collected from restoration sites in Greater Farallones National Marine Sanctuary have been transported to West Marin Compost in Marin County. A total of 117,847 pounds of purple urchins have been added to the compost mix as of July 2025, according to the National Oceanic and Atmospheric Administration (NOAA). Since 2023, 117,847 pounds of urchins have been added to the compost.
Jeff Creque, a consultant with West Marin Compost, said,”Urchins are a great source of nitrogen, calcium, and micronutrients. California sanctuary is removing purple sea urchins from areas targeted for kelp restoration and giving them a second use as compost. Removing the urchins helps reduce their numbers near bull kelp, which gives the kelp a better chance to survive, reach adulthood, and release spores. The animals also provide nitrogen, calcium, and micronutrients that enrich compost used by local farmers and gardeners. The purple urchins are harvested by hand from areas selected for their high potential for kelp restoration. The effort is led by the Greater Farallones Association, along with Greater Farallones and Cordell Bank National Marine Sanctuaries. After being collected, the urchins are transported to West Marin Compost, where they are added to the compost mix. At West Marin Compost, the harvested urchins add nutrients to compost used by local agriculture. We are happy to have a bit of the sea added to our material”. The composting effort gives the purple urchins collected from kelp restoration areas a new purpose by turning them into material that can support farmers and gardeners. The wider restoration project also involves work with Northern California’s Tribal community, research at sites where kelp has persisted, collaboration with commercial urchin divers to remove urchins from restoration areas, and kelp outplanting. Together, these activities support the broader effort to restore the ecosystem. You use AI every day. Now get your AI Quotient. Take the AIQ test.
Because they are starving after losing much of their bull kelp food supply, purple urchins collected during the restoration work have little commercial value. Local divers collect the urchins at restoration sites and send them for composting instead of exporting these animals for food. This gives the animals another purpose while supporting the restoration effort. Once composted, the urchins become part of material used to grow food, connecting kelp restoration with local agriculture.
They may remain in this condition for years and produce very little uni, a prized delicacy once obtained from healthy red urchins in the sanctuary and along the Sonoma and Mendocino coasts before the major kelp die-off.
Commercial urchin diver Erik Owen has been collecting the animals for the restoration project since 2023. Greater Farallones National Marine Sanctuary has experienced a catastrophic loss of bull kelp since 2014 following a series of events. Because of different stressors, pC: Matt Lauchenauer/Dandy Fish Company/ National Oceanic and Atmospheric Administration (NOAA) Purple urchins feed on kelp, and their numbers can rise sharply when kelp forests decline.
Reducing the number of purple urchins around bull kelp gives the plants more opportunity to survive, mature, and release spores that can produce the next generation. The harvested urchins are then taken to West Marin Compost, where they become part of the composting process. As the kelp declined, purple urchins became a dominant part of the nearshore environment and continued feeding on the remaining bull kelp. The restoration effort focuses on areas where kelp has a strong chance of recovery.
