Since around 2014, bull kelp forests along the Sonoma and Mendocino coastline have lost as much as 95% of their coverage in the hardest-hit areas — 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.
With their main predator gone, purple urchin numbers exploded to roughly 60 times their historical average. Where dense kelp forests once stood, urchins grazed the seafloor down to bare rock — what researchers call an “urchin barren” — leaving little for new kelp to take hold on.
Recovery has been slow and patchy. Groups including the Greater Farallones National Marine Sanctuary are working with commercial urchin divers and local fishers on removal efforts, clearing urchins by hand to give kelp spores a chance to resettle.
Further reading: [ links to the original sources this story was drafted from go here ]