Environmental Disaster Continues to Decimate Bull Kelp Forests and Red Abalone Populations in Northern California

The California Department of Fish and Wildlife (CDFW) has monitored northern California kelp forest ecosystems and red abalone populations for the past 20 years. Surveys completed in the summer of 2018 continued to document mass abalone starvation and population collapse. A limited survey effort in 2019 saw no improvement in environmental conditions for red abalone populations.  On average, for Sonoma and Mendocino counties combined, red abalone densities have been reduced by 75 percent since 2014.

“Sonoma and Mendocino counties were the heart of both the bull kelp forest and the recreational red abalone fishery, but now bull kelp has all but disappeared along this coastline,” said Dr. Laura Rogers-Bennett, after completing Mendocino County dive surveys from the CDFW patrol vessel Steelhead. “As a result, our divers are seeing mass abalone mortalities and piles of red abalone shells in sites that used to have dense abalone populations.”

abalone density table
click to enlarge

The recreational red abalone fishery has been closed since April, 2018 due to the ongoing environmental disaster that has significantly impacted the abalone resource and the whole kelp forest ecosystem. The most serious facet of the disaster is the dramatic decline in kelp forests since 2014, brought about by the interplay of a sea star die-off (2013), an ocean heat wave (2014-2016), and a population boom of purple sea urchin (2015- ongoing), which competes with abalone for food (kelp). Only seven percent of the bull kelp canopy documented in 2014 now remains along more than 200 miles of northern California coastline.

Kelp is a primary food source for abalone and many other ocean “grazers”, and provides shelter and hunting grounds for fish, invertebrates and marine mammals. Expanded populations of purple sea urchins reduced the robust kelp forests off the northern California coast to unproductive “urchin barrens” within a few years’ time.

The commercial sea urchin fishery, which harvests red sea urchin for the roe they produce, is also feeling the impact of the environmental disaster. With so little kelp remaining, the urchins are no longer full of roe, and are of no value to the fishery.

CDFW has been actively involved in helping to form a coalition of agencies, universities, NGOs, and citizen groups to address the kelp forest decline in the group KELPRR. This group is now working on kelp restoration, urchin control, developing urchin ranching, abalone conservation, and many other kelp restoration actions.

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post by Dr. Laura Rogers-Bennett, CDFW Senior Environmental Scientist, and Mary Patyten, CDFW Research Writer