Presenter: Kyle Cavanaugh (UCLA)

Description:
Between 2013 and 2015 the abundance of bull kelp forests along the coast of northern California collapsed, declining by more than 90% due to a combination of stressors including a marine heatwave, mass mortality of sea stars, and an explosion in the population of sea urchins, a major grazer of kelp. While the spatial scale of this collapse was large (> 300 km of coastline), there were local areas of ‘kelp refugia’ across this region where kelp exhibited resilience to these stressors. In addition, there have been local observations of recovery during the past year. We used high-resolution Planet satellite imagery (3 m) to map kelp canopy dynamics along the coast of northern California over six years following the initial collapse (2016-2021) and examined patterns and drivers of recovery. While kelp abundance remained at historically low levels from 2016 to 2020, there were signs of recovery in 2021, with kelp canopy area increasing by 2.8x between 2020 and 2021. Spatial patterns of recovery appeared to be linked to connectivity to kelp refugia, suggesting that refugia play an important role in regional recovery.  These results can inform strategies for kelp forest conservation and restoration, e.g., restoration site prioritization.