Since around 2014, bull kelp forests along the Sonoma and Mendocino coastline have lost more than 90% of their canopy (in the hardest-hit stretches, closer to 95%), one of the steepest kelp declines recorded anywhere on the West Coast.
The collapse traces back to two things happening at once. Sea star wasting disease had already wiped out huge numbers of sunflower stars, one of the main predators keeping purple sea urchins in check. Then a multi-year marine heatwave, followed by a strong El Niño, warmed coastal waters and starved kelp of the cold, nutrient-rich water it needs to grow. Purple urchin density in surveyed areas jumped roughly 60-fold in a single year, from under 2 per square meter to as many as 13.
With their main predator gone, urchins grazed the seafloor down to bare rock, what researchers call an “urchin barren,” leaving little for new kelp to take hold on. The lost fishing is real money, too: the region’s recreational abalone fishery was worth an estimated $44 million a year before it closed, and the commercial urchin fishery around $3 million.
Recovery is now getting real federal backing. Efforts are underway up and down the coast to help kelp resettle these barrens by hand, outplanting spores onto cleared rock and removing urchins directly, one stretch of coastline at a time. The details of one such project, funded by a $4.9 million NOAA grant, are below.
Further reading: Rogers-Bennett & Catton, “Marine heat wave and multiple stressors tip bull kelp forest to sea urchin barrens,” Scientific Reports (2019); NOAA Fisheries, “Pioneering Project to Restore Bull Kelp Forests in Greater Farallones National Marine Sanctuary” (2024).