A tale of two sea stars: recovery (ochre star) or endangerment (sunflower star) following the 2014 epidemic

During the summers of 2013 and 2014, populations of sea stars along the west coast from Alaska to Mexico were decimated by the sea star wasting disease (SSWD) epizootic. Two of the most highly affected species along this range are Pisaster ochraceus (the ochre star), the most common intertidal species, and Pycnopodia helianthoides (the sunflower star), the most common subtidal species, both of which are endemic to the western coast of the U.S. For the ochre star, in the San Juan Islands of Washington State, we measured high case fatality rates associated with disease prevalence over 90% during the summer of 2014. Low levels of disease were observed in the summers of 2015, 2016, and 2017. Population levels following the epizootic remain stable but small, and shifted in size structure from larger to smaller stars. At one site, a dramatic increase in both juvenile and adult ochre stars occurred in 2017, giving hope for future recovery. In contrast, the most common subtidal species, the sunflower star, also suffered catastrophic mortality in 2014. However, in this case, Citizen Science Monitoring in all oceanographic basins of the Salish Sea through 2017 shows an extraordinary decimation of this species, with no sign of recovery three years after the SSWD epizootic. Extremely low population size of sunflower stars raises concern about the capacity of this species to recover, as well as to resist other stochastic events in the future