Data from: Sudden collapse of a mesopredator reveals its complementary role in mediating rocky reef regime shifts

While changes in the abundance of keystone predators can have cascading effects resulting in regime shifts, the role of mesopredators in these processes remains underexplored. We conducted annual surveys of rocky reef communities that varied in the recovery of a keystone predator (sea otters Enhydra lutris) and the mass mortality of a mesopredator (sunflower sea star Pycnopodia helianthoides) due to an infectious wasting disease. By fitting a population model to empirical data, we show that sea otters had the greatest impact on the mortality of large sea urchins, but that Pycnopodia decline corresponded to a 311% increase in medium urchins and a 30% decline in kelp densities. Our results reveal predator complementarity in size-selective prey consumption strengthens top-down control on urchins, affecting the resilience of alternative reef states by reinforcing kelp forests and eroding urchin barrens. We reveal previously underappreciated species interactions within a 'classic' trophic cascade and regime shift, highlighting the critical role of middle-level predators in mediating rocky reef state transitions.READMEThis file explains all of the variables in each of the datasets required to conduct the analyses used in the article: "Sudden collapse of a mesopredator reveals its complementary role in mediating rocky reef regime shifts." These data files were generated from subtidal SCUBA surveys collected over four years (2013-2016) at 11 rocky reef sites on the central coast of British Columbia led by Jenn M. Burt, Kyle W. Demes, and Anne K. Salomon.Burt_CC-DiveSurveys2013-2016_QuadCountsThis data file has information for counts of red urchins (within size categories) and all adult kelp species (Laminariales, stipes >15cm) within 1x1m quadrats (n=18), across 11 survey sites conducted annually over 4 years (2013-2016) on the central coast of BC, Canada.Burt_CC-DiveSurveys2013-2016_Site_Sum_statsThis data file has information summarized for each annual subtidal survey site (n=11) across all survey years (n=4) for sea otter occupation, Pycnopodia biomass, density and biomass of red sea urchins (sm, med, lg), kelp density. Surveys conducted on the central coast of BC (2013-2016).Burt_CC-DiveSurveys2013-2016_UrchSizeThis data file is used for running the simulation code to estimate urchin growth transition probabilities (details in electronic supplementary material, Appendix M1). This data file is a continuous list containing every single entry for every recorded and measured (to the nearest cm) red urchin (n=3451) across all quadrats (n=18 per site, each 1x1m) from all sites (n=11) in all years (n=4, 2013-2016).Burt_et_al_analysis_codeThis is an R markdown file that contains all the code to run all of the analyses in the Burt et al. paper "Sudden collapse of a mesopredator reveals its complementary role in mediating rocky reef regime shifts.