Extreme climatic events have recently impacted marine ecosystems around the world, including foundation species such as corals and kelps. Here, we describe the rapid climate-driven catastrophic shift in 2014 from a previously robust kelp forest to unproductive large scale urchin barrens in northern California. Bull kelp canopy was reduced by >90% along more than 350 km of coastline. Twenty years of kelp ecosystem surveys reveal the timing and magnitude of events, including mass mortalities of sea stars (2013-), intense ocean warming (2014–2017), and sea urchin barrens (2015-). Multiple stressors led to the unprecedented and long-lasting decline of the kelp forest. Kelp deforestation triggered mass (80%) abalone mortality (2017) resulting in the closure in 2018 of the recreational abalone fishery worth an estimated $44 M and the collapse of the north coast commercial red sea urchin fishery (2015-) worth $3 M. Key questions remain such as the relative roles of ocean warming and sea star disease in the massive purple sea urchin population increase. Science and policy will need to partner to better understand drivers, build climate-resilient fisheries and kelp forest recovery strategies in order to restore essential kelp forest ecosystem services.

A restoration program including wild population surveys, captive breeding, health monitoring, recovery site preparation, and recovery modeling has been implemented to restore white abalone (Haliotis sorenseni) populations in California. White abalone once supported a lucrative fishery and are now endangered, nearing extinction at less than 1% of baseline abundances. Recent deep water surveys indicate that populations continue to decline with no signs of recruitment, despite the closure of the fishery in 1996. Four sites with artificial reefs (n ¼ 12/site) in optimal white abalone habitat were established. No wild white abalone have been found at these sites. Captive abalone were spawned in the spring of each year from 2012 to 2015. Each year, the production of 1-y-old abalone has increased in the captive breeding program from approximately 20 in 2012, to 150 in 2013 and an estimated 2,000 in 2014. In 2015, the breeding program reached two milestones: (1) most successful spawning season to date and (2) the hatchery distributed 200 captive-reared abalone to 4 partner institutions within the White Abalone Recovery Consortium (WARC). The WARC is made up of federal and state agencies, universities, public aquaria, and aquaculture organizations, all committed to white abalone restoration. The next steps for the program include expanding the captive breeding program to increase production, monitoring abalone health and genetic diversity, and conducting stocking studies to enhance growth and survival in the ocean. The goal of the stocking program is to create a reproductive population in the wild to bring white abalone back from the brink of extinction.

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ABSTRACT1. Identifying appropriate ecological conditions for population restoration is important for endangered species such as black abalone (Haliotis cracherodii) in California, but limited information exists regarding restoration locations.2. Using a combination of ancient and historical archaeological data and modern commercial fishing records, four optimal locations for restoration based on past relative abundances of black abalone were identified: north-western, north-eastern, and south-central San Miguel Island and western San Nicolas Island.3. These locations around California's Channel Islands have supported dense black abalone populations for at least 10 000 years and may offer optimal environmental conditions to enhance the success of black abalone restoration.4. The strategy outlined here illustrates the promise of integrating prehistoric, historical, and modern fishery data to inform restoration of threatened and endangered abalone, oysters, and other shellfish around the world.

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