The keystone species Pisaster ochraceus was severely affected by SSWS over much of its range. In Oregon, their populations declined by 50-94%. Because P. ochraceus aids in maintaining fast-growing Mytilus californianus populations from overgrowing intertidal zones (Paine, 1966, 1969, 1974), declines in their populations have resulted in trophic cascades and regime shifts in intertidal regions (Burt et al., 2018; Miner et al., 2018; Schultz, Cloutier, & Côté, 2016). Loss of P. ochraceus due to SSWS could have detrimental impacts on coastal ecosystems. It is likely that SSWS has exerted strong selection on P. ochraceus populations. Recent genetic studies on this and other affected sea star species are suggestive of a genetic component to variation in SSWS susceptibility. Individuals of P. ochraceus with SSWS symptoms showed elevated expression levels in genes associated with immune response and tissue remodeling (Fuess et al., 2015; Gudenkauf & Hewson, 2015; Ruiz‐Ramos, Schiebelhut, Hoff, Wares, & Dawson, 2020). In addition, Schiebelhut et al. (2018) observed allele frequencies shifts before and after peak SSWS outbreaks in California populations. More specifically, they detected changes in restriction site-associated DNA sequencing (RAD-seq) haplotype frequencies between pre-SSWS adults and post-SSWS adults, as well as between pre- SSWS adults and recruits in the populations after SSWS. These changes occurred in few loci, but were consistent across independent geographic samples (Schiebelhut, Puritz, & Dawson, 2018).  However, because Schiebelhut et al. (2018) genotyped only apparently normal individuals (asymptomatic), it is still unclear whether the allele shifts were caused by the disease itself or by other co-occurring factors. 
Here, we build upon their work by investigating genomic differences between wasting individuals (i.e., presenting with SSWS) and grossly, or apparently normal individuals from the same localities during an outbreak of SSWS. We examine genetic variation in 200 P. ochraceus individuals collected in central Oregon in 2016, two years following the initial spring 2014 SSWS outbreak in Oregon (Menge et al. 2016). At this time, both apparently normal and wasting sea stars were common at each of the six Oregon sites sampled. We reasoned that, by being found on the same transects as wasting individuals and hence likely exposed to similar conditions, sea stars found to be apparently normal may carry genetic variants associated with resistance or tolerance to SSWS. By combining field surveys of natural disease prevalence with high-throughput single nucleotide polymorphism (SNP) genotyping, we assess the contribution of sea star genetic variation to SSWS occurrence. Our  dataset is the result of a unique opportunity to compare apparently normal and wasting individuals from the same time and place during the SSWS epidemic.