Thu, Aug 18, 2022: 2:30 PM-2:45 PM
513D
Background/Question/MethodsBetween 2013 and 2015 the abundance of bull kelp forests along the coast of northern California collapsed, declining in area by more than 90% due to a combination of stressors including a marine heatwave, sea star wasting disease, 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. These refugia may be important to regional recovery because they provide a spore source for recolonization of empty habitat. The goal of this study was to examine the role of kelp refugia in recolonization and regional recovery of bull kelp forests. We used high-resolution (3 m) Planet satellite imagery 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. We calculated the connectivity of potential habitat to refugia and examined the relationship between connectivity and probability of recolonization.
Results/ConclusionsWhile kelp abundance remained at historically low levels from 2016 to 2020, there was a large increase in bull kelp abundance in 2021, with kelp canopy area recovering to ~80% of pre-heatwave levels. Spatial patterns of recovery appeared to be driven by a combination of spatial variability in grazing pressure and connectivity to kelp refugia. Habitat that was closer to kelp refugia was significantly more likely to be recolonized in 2021. We used our connectivity metrics to infer areas where recovery was limited by spore dispersal vs. grazing pressure. Our results provide insight into the role of persistent kelp refugia in regional scale recolonization, which can inform strategies for kelp forest conservation and restoration, e.g., restoration site prioritization.
Results/ConclusionsWhile kelp abundance remained at historically low levels from 2016 to 2020, there was a large increase in bull kelp abundance in 2021, with kelp canopy area recovering to ~80% of pre-heatwave levels. Spatial patterns of recovery appeared to be driven by a combination of spatial variability in grazing pressure and connectivity to kelp refugia. Habitat that was closer to kelp refugia was significantly more likely to be recolonized in 2021. We used our connectivity metrics to infer areas where recovery was limited by spore dispersal vs. grazing pressure. Our results provide insight into the role of persistent kelp refugia in regional scale recolonization, which can inform strategies for kelp forest conservation and restoration, e.g., restoration site prioritization.