Award: OCE-1737381

Intellectual Merit: Mass mortality events provide opportunities to explore what makes species more or less sensitive to environmental change, and quicker or slower to recover. We explored these questions surrounding an outbreak of sea star wasting (SSW) in the northeastern Pacific, focusing on the ochre star (Pisaster ochraceus), an ecologically important species decimated by the disease in 2013. Sampling ochre stars from Alaska to Baja California, from before and after the outbreak, and annually thereafter for 6 years, allowed us to generate a chromosome-scale reference genome, compare genetic diversity before and after the outbreak, contrast wasting versus non-wasting animals, describe genetic diversity across the species' range, and genotype 850 stars spanning a period of 5 years. While analyses still continue, our study has revealed that Pisaster ochraceus showed significant change in allele frequencies in response to the outbreak, that gene expression differs between wasting and non-wasting animals, that loci responding to wasting are associated with innate immunity and chemical defense, consistent with stress responses, cellular 'suicide', and tissue degradation, and that recovery in this species was sufficiently rapid to avoid substantial loss of neutral genetic diversity. However, alone, the analyses of ochre stars did not tell us why the broader community showed highly variable responses to SSW. As such we also sampled five additional species of sea star for population dynamics, reference genome assembly, comparative phylogenomics, population genetics, and scanned the literature to provide the taxonomically most inclusive description of SSW-associated dynamics beginning in 2013. We concluded that: predominantly a dozen shallow water species declined, with another fifteen species indicated to be susceptible; SSW prevalence was as high as 80% during the peak and 35% subsequently, depending on species and location; despite populations collapsing rapidly, environmental and species variation drew out the outbreak for 2-3 years before diminishing to chronic background rates of ~2%; recruitment began immediately in many species, but was spatially heterogeneous; and elevated temperatures, decreased wave exposure, and freshwater discharge were the abiotic stressors most associated with SSW whether or not a pathogen was involved. Our analyses also raised the specter of declines of deeper water species in 2013 and 2019. Broader Impacts: Our research charting the demography and health of sea stars established criteria for identifying genes associated with susceptibility to SSW and those that may respond to other stressors, such as warming, de-oxygenation, and acidification. This work formed the foundation for emerging conservation efforts for sea stars, particularly the sunflower star Pycnopodia helianthoides, and has been translated into a multi-institutional program for genomic restoration and captive breeding to enhance kelp forest recovery. The genomic resources deposited in public repositories also are catalyzing independent research by other investigators. This project involved 66 volunteers -- of which 71% identified as women and 25% as Hispanic, groups that have been underrepresented in the marine sciences -- providing mentoring and training in fieldwork, laboratory research, bioinformatics, and scientific presentation. We also raised awareness of threats to coastal health and the need for conservation among citizen scientists and undergraduates involved in the project and through regional and national media. Two graduate students and three postdocs / research scientists were mentored in fieldwork, molecular lab work, bioinformatics, project management, and scientific communication (grant writing, manuscript preparation, and presentation skills); three have entered the work force as faculty at a community college, a primarily undergraduate-serving public university, and an historically black university; a fourth is working in the non-profit conservation sector. Last Modified: 01/20/2024 Submitted by: MichaelNDawson