For the past two years volunteer recreational scuba divers organized by the Giant Giant Kelp Restoration Project (G2KR) have been culling sea urchins at a demonstration site in Monterey in an effort to restore the area’s once lush kelp forests. The effort has been monitored by Reef Check using citizen science divers in partnership with G2KR, California Department of Fish & Wildlife, Ocean Protection Council, and the Monterey Bay National Marine Sanctuary.
According to the latest Reef Check data, urchin densities dropped from over 800 urchins per 100m2 in April of 2021 to less than 100 urchins per 100m2 by June of 2022. The density of giant kelp increased roughly five fold from 33 stipes per 100m2 in April of 2021 to 150 per 100m2 in September of 2022. In a nearby control area, in which urchins were not removed, no noticeable change was observed.
Purple sea urchins are native species of California’s kelp forests, but following the loss of kelp during the 2015/16 Marine Heatwave and the loss of the sunflower seastar, a key urchin predator, their populations have dramatically increased. These voracious herbivores are able to devour kelp and turn lush kelp forest into “urchin barrens”, areas that contain urchins, bare rock, and a much lower abundance and diversity of the myriad species that inhabit kelp forests.
In early 2021 the California Fish & Game Commission enacted a rule change allowing the unlimited take of sea urchins at Tankers Reef in Monterey, located just east of the commercial pier and offshore of Del Monte beach. Since that time, trained recreational divers with G2KR have worked in that area culling urchins by smashing them with hammers.
Urchin density was dramatically reduced by the fall of 2021, but kelp didn’t start growing until the start of the spring 2022 growing season. Over the summer Reef Check divers have continued to observe increases in kelp. Reef Check staff and volunteers will continue to conduct ongoing monitoring to assess the success and health of the reef.