urchins on kelp
Photo: Dan Schwartz

What happened to the kelp?

Since 2014, bull kelp forests in northern California have declined by over 90 percent due to a combination of extreme warm water events (marine heatwaves and El Niño), a loss of predatory species like the sea otter and sunflower sea star, and dramatic increases in native purple sea urchin populations. The combination of these stressors was too much for kelp forests to persist, and they transitioned into “urchin barrens”. To learn more about kelp forest and urchin barren dynamics, click here.

What are we doing to address this?

Reef Check is testing if a reduction in herbivores (urchins) will facilitate kelp re-growth. At several locations in central and northern California, we will explore different methods to reduce purple urchin populations and promote kelp growth. These sites were chosen as restoration sites because they show potential for kelp recovery and because they are of particular interest to the local communities of recreational divers and fishers.

Mendocino County Restoration Project

purple urchins in nets

A team of ecologists from Reef Check and local Fort Bragg commercial urchin fishermen are involved in a state-funded effort to remove urchin as means for restoring the kelp ecosystem. Commercial urchin divers are removing urchins from the reef and Reef Check is guiding and monitoring the effectiveness of this approach. After urchins are removed from restoration sites, they are landed in Fort Bragg harbor and dissected by Reef Check staff and volunteers to better understand what they eat and their reproductive capacity. Ultimately, we hope to facilitate a reverse shift from urchin barrens back to kelp forests and understand the associated costs and benefits. By working with the commercial fishermen, this project also provides economic benefits to one of the communities hardest hit by the loss of the kelp forest and fisheries it used to support.

Lover’s Point Kelp Forest Restoration Experiment

urchins on holdfast

In Monterey County, a select team of Reef Check volunteers are investigating at what density of sea urchins giant kelp can reestablish reefs in central California. Under the guidance of Reef Check scientists, these volunteers are establishing different density levels on experimental reefs. They are experimenting with different removal methods and schedules to maintain low densities on these reefs. Initial results suggest that if urchins are removed at short time intervals and urchin migration to those reefs is controlled, kelp is able to recruit and grow. Results from this small scale experiment will be used to inform larger scale restoration efforts in central California and elsewhere.

Tanker Reef Kelp Forest Restoration Project

In December 2020, the California Fish and Game Commission (FGC) adopted an amendment that allows divers with a California sport fishing license to take unlimited purple sea urchin and red sea urchin at Tanker Reef in Monterey County. The goal of this amendment is to allow recreational divers to remove urchins in order to restore kelp forest at this site. Reef Check is working with the California Department of Fish and Wildlife (CDFW), California Ocean Protection Council (OPC), and Monterey Bay National Marine Sanctuary (MBNMS) to monitor this kelp restoration effort to address some of the following key management questions:

  • Can divers operating under the proposed sea urchin sport harvest regulations reduce sea urchin densities to levels expected to facilitate kelp regrowth?
  • Does reduction of sea urchin grazing pressure facilitate natural kelp regrowth?
  • Are there negative impacts associated with urchin culling (e.g. bycatch, damage to underlying reef structure, disturbance to marine mammal populations)?
divers removing urchins
Photo: Patrick Webster