Selection and Genetic Succession in the Intertidal – Population Genomics of Pisaster ochraceus During a Wasting Disease Outbreak and its Aftermath (OCE-1737127)

This project seeks to understand the outcomes of predator-disease dynamics by exploring a recent pandemic that decimated 90% of ochre sea stars (Pisaster ochraceus) in the eastern North Pacific in 2013. The research team will explore how recovery may depend upon often difficult-to-see processes such as the interplay of migration and natural selection in marine species. While the population of sea stars is currently rebounding due to several years of unusually high recruitment, the sea star wasting disease continues to persist at low levels. This project aims to determine the genetic consequences of the pandemic and subsequent recovery. The team will determine whether the majority of susceptible sea stars have died and identify possible refuges where susceptible sea stars survived. They will examine the potential for heritable variation in resistance to this disease in order to assess whether the new recruits are tolerant or susceptible to wasting. Resolving these issues will enable predictions about the trajectory of their recovery and the potential responses to future large scale disease outbreaks. Research findings will be shared with resource managers and scientists at a collaborative workshop that will focus on state-of-the-art methods to advance research on marine diseases. The public will have the opportunity to learn more about sea star wasting disease through a partnership with the UCSC Seymour Marine Discovery Center and can track the incidence of disease using an online interactive map available at Results will be incorporated into professional development for teachers with CalTeach and adapted for teaching materials up to college-level. This project will train diverse early career scientists – undergraduates, graduates, and a postdoctoral scholar – in integration of ecological and genomic methods.


Understanding the consequences of large-scale pandemics in the broader contexts of geographic heterogeneity and chronic changes in ocean pH and temperature is an emerging contemporary issue. This project employs long-term characterization of population dynamics and genetic consequences of a sea star wasting disease (SSWD) outbreak, which caused median 90% mortality in Pisaster ochraceus populations in the northeastern Pacific, to estimate potential long-term consequences for the species. While the largest recorded influx of new recruits occurred in 2014-2016, it is unknown where they originated from, whether recruits and surviving adults remained susceptible to the disease, which persisted at low levels, and for how long these dynamics might continue. This long-term dataset provides a unique opportunity for exploring the short and long term repercussions of such large-scale disease outbreaks and the population dynamics that they precipitate. This project builds on long-term field studies of wild populations to describe host population dynamics, the disease, and genomic diversity. The goal is to discover genetic variation associated with SSWD and to dissociate that variation from population genomic effects attributable to abiotic environmental variation. Objectives are: (1) Census P. ochraceus at 24 sites throughout its range to describe population dynamics, the prevalence of SSWD, and measure abiotic variables. (2) Conduct laboratory experiments coupled with RNAseq analyses to determine loci differentially regulated during exposure to SSWD, temperature, salinity, and pCO2 anomalies. (3) Map ddRAD, RNAseq, and candidate loci under selection to a P. ochraceus genome. (4) Conduct range-wide population genomic analyses for 3 years to assess genetic (SNP) variation among wild-caught specimens with, versus without, SSWD across a geographic mosaic of abiotic variation. (5) Explore links between SSWD and candidate loci, such as EF1A. These analyses will describe the immediate genomic consequences of the disease outbreak, the population dynamics that the outbreak set in motion, and the interplay of factors and mechanisms – such as disease, temperature, migration, selection – that affected these changes. The results will advance understanding of general processes and interactions that shape population genomic structure in coastal ecosystems, providing resources to inform future research and applications in design of management strategies for coastal living resources.

Publications on this project to date:

Jackson EW, Pepe-Ranney C, Johnson MR, Distel D, Hewson I (in press) “A highly prevalent and pervasive densovirus discovered among sea stars from the North American Atlantic Coast” Applied and Environmental Microbiology

Hewson I (2019) “Technical pitfalls that bias comparative microbial community analyses of aquatic diseases” Diseases of Aquatic Organisms. 137: 109-124

Hewson I, Sullivan B, Jackson EW, Xu Q, Long H, Lin C, Quijano Cardé EM, Seymour J, Siboni N, Jones MRL, Sewell MA (2019) “Perspective: Something old, something new? Review of wasting and other mortality in Asteroidea (Echinodermata)” Frontiers in Marine Science

Jackson EW, Pepe-Ranney C, Debenport SJ, Buckley DH, Hewson I (2018) “The microbial landscape of sea star and anatomical and interspecies variability of their microbiome” Frontiers in Microbiology.

Hewson, I, Bistolas, KSI, Quijano Cardé, EM, Button JB, Foster PJ, Flanzenbaum JM, Kocian J, Lewis CK (2018) “Investigating the complex association between viral ecology, environment and North Pacific sea star wasting” Frontiers in Marine Science 5:77