Surf to Turf! Sea Urchins From Marine Sanctuary Restoration Project Recycled as Compost

Jul 16, 2025

purple urchins being offloaded from a big white box with use of heavy machinery, surrounded by piles of compost soil. — Purple urchins harvested at kelp restoration sites in Greater Farallones National Marine Sanctuary are composted to support beneficial soil health for local agriculture. Credit: Matt Lauchenauer/Dandy Fish Company

Gardeners and farmers in Marin County, California may notice a purple hue in the compost they purchase this year! Since 2023, urchins harvested from kelp restoration areas in Greater Farallones National Marine Sanctuary are contributing to enriching compost at West Marin Compost.

purple spiky urchins covering the seafloor with kelp in the distance — Purple urchins are dominating the nearshore environment, while consuming bull kelp. Photo: Steve Lonhart/NOAA

You might be wondering, 'why are these sea urchins being composted?' Purple sea urchins eat kelp, and in areas where kelp stands are declining due to various stressors, the sea urchin populations can expand unchecked. As part of a kelp restoration effort led by Greater Farallones Association and Greater Farallones and Cordell Bank National Marine Sanctuaries, purple urchins have been meticulously harvested by hand in areas targeted for their high kelp restoration potential.Those urchins are then transported and offloaded at West Marin Compost. Since starting this effort, 117,847 pounds have entered the compost mix. Reducing purple urchin populations near bull kelp gives the kelp a better chance to survive, reach adulthood, and release spores to grow the next generation.

"Urchins are a great source of nitrogen, calcium, and micronutrients. We are happy to have a bit of the sea added to our material," says Jeff Creque, consultant with West Marin Compost.

Person with hat standing in front of a crate of purple urchins filled to the brim. — Commercial Urchin Diver Erik Owen has been harvesting purple urchins as part of this restoration project since 2023. Photo: Gina Contolini/NOAA/GFA

These purple urchins have little commercial value as seafood because they're starving—due to a lack of bull kelp to eat. Starved urchins can persist in this state for years, offering minimal uni, the prized delicacy once harvested from healthy red urchins in the sanctuary and along the Sonoma and Mendocino coasts before the massive kelp die-off. Greater Farallones National Marine Sanctuary has witnessed a catastrophic loss of bull kelp since 2014 due to a series of events. Greater Farallones and Cordell Bank National Marine Sanctuaries and Greater Farallones Association are leading collaborative efforts with experts to research the best methods to restore this vital ecosystem.

Thanks to the kelp restoration efforts, local urchin divers who are part of the restoration project now harvest purple urchins at the sanctuary restoration sites; yet, instead of exporting these animals for food, they are being used to help grow other food by local recycling through composting.

The project includes work with Northern California's Tribal community, understanding conditions at sites where kelp has persisted, working with commercial urchin divers to remove urchins within restoration sites, and outplanting kelp.