Abstract
The recent outbreak of Sea Star Wasting Disease (SSWD) is one of the largest marine epizootics in history, but the host-associated microbial community changes specific to disease progression have not been characterized. Here, we sampled the microbiomes of ochre sea stars, Pisaster ochraceus, through time as animals stayed healthy or became sick and died with SSWD. We found community-wide differences in the microbiomes of sick and healthy sea stars, changes in microbial community composition through disease progression, and a decrease in species richness of the microbiome in late stages of SSWD. Known beneficial taxa (Pseudoalteromonas spp.) decreased in abundance at symptom onset and through disease progression, while known pathogenic (Tenacibaculum spp.) and putatively opportunistic bacteria (Polaribacter spp. and Phaeobacter spp.) increased in abundance in early and late disease stages. Functional profiling revealed microbes more abundant in healthy animals performed functions that inhibit growth of other microbes, including pathogen detection, biosynthesis of secondary metabolites, and degradation of xenobiotics. Changes in microbial composition with disease onset and progression suggest that a microbial imbalance of the host could lead to SSWD or be a consequence of infection by another pathogen. This work highlights the importance of the microbiome in SSWD and also suggests that a healthy microbiome may help confer resistance to SSWD.