Kyle Cavanaugh1, Katherine Cavanaugh1
1University of California, USA
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, 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. In subsequent years, regional kelp abundance has remained at historically low levels; however, there has been local recovery in some locations. 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 Planet satellite imagery (3 m) to map kelp canopy dynamics along the coast of northern California over nine years following the initial collapse (2016-2024) 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. Spatial patterns of recovery appeared to be driven by a combination of physical factors (e.g., sea surface temperature and nutrient levels), spatial variability in grazing pressure, and seascape characteristics (e.g., connectivity to kelp refugia). Our findings highlight the importance of persistent kelp refugia in supporting regional-scale recovery, offering valuable insights for kelp forest conservation and restoration efforts, such as prioritizing restoration sites.
Biography
Kyle Cavanaugh is a Professor in the Department of Geography at University of California, Los Angeles and Vice Director of the UCLA Marine Center. He studies the drivers and consequences of changes in coastal foundation species such as kelp forests and mangroves. He is especially interested in what controls large-scale changes in the distribution and abundance of these species. Much of his research utilizes remote sensing (e.g. satellite, aerial, and UAV imagery) to document ecological change.