Award: OCE-1737127

Pisaster ochraceus (the ochre sea star) is a keystone predator on the north American west coast. Sea star wasting disease (SSWD) is a condition that has affected over 20 species of asteroids in the northeast Pacific since 2013, and has heavily affected ochre star populations. Marine diseases like SSWD place considerable pressures on the genetic diversity of affected species, which can be observed by sequencing their genomes. While initially believed to be a result of viral infection, this project identified an important role of microorganisms that inhabit and grow in waters immediately above sea star surfaces in generating SSWD. Because sea stars breathe through their skin, disturbance in oxygen concentrations around individuals results in tissue damage and in some cases animal death. The root cause of SSWD is likely enrichment of organic matter that is exuded by algae, which fuels microorganisms and in turn draws down available oxygen very close to their surfaces. This effect is made worse when the water is warm (e.g. in late summer), since oxygen concentrations in water are inversely related to water temperature, and microorganisms grow faster (and use up more oxygen) under warmer conditions. Hence, work on this project focused on understanding whether genes that were selected by decreased oxygen concentrations and added algal organic matter were the same as those seen in sea stars that survived mass mortality in 2013-2014, and their progeny. Several genes that are highly responsive to available oxygen were among those observed in today’s populations compared to sea stars collected prior to 2013. We also observed several genes in transcriptomes prepared from samples in 2013-2014 comparing healthy and disease which were involved in low-oxygen stress responses. Work to define genes that are selected for by organic matter are under investigation through an ongoing collaborative project (OCE- 1737091). This project has trained several undergraduate and graduate students, and formed the basis of a publically-available online presentation aimed at pre-school age students and a publically accessible seminar through the Shoals Marine Laboratory. Last Modified: 12/01/2020 Submitted by: Ian Hewson