Sea stars resist wasting through active immune and collagen systems

Epidemics are becoming more common and severe, however, pinpointing the causes can be challenging, particularly in marine environments. The cause of sea star wasting (SSW) disease, the ongoing, largest known panzootic of marine wildlife, is unresolved. Here, we measured gene expression longitudinally of 24 adult Pisaster ochraceus sea stars, collected from a recovered site, as they remained asymptomatic (8 individuals) or naturally progressed through SSW (16 individuals) in individual aquaria. Immune, tissue integrity and pro-collagen genes were more highly expressed in asymptomatic relative to wasting individuals, while hypoxia-inducible factor 1-α and RNA processing genes were more highly expressed in wasting relative to asymptomatic individuals. Integrating microbiome data from the same tissue samples, we identified genes and microbes whose abundance/growth was associated with disease status. Importantly, sea stars that remained visibly healthy showed that laboratory conditions had little effect on microbiome composition. Lastly, considering genotypes at 98 145 single-nucleotide polymorphism, we found no variants associated with final health status. These findings suggest that animals exposed to the cause(s) of SSW remain asymptomatic with an active immune response and sustained control of their collagen system while animals that succumb to wasting show evidence of responding to hypoxia and dysregulation of RNA processing systems.