Precursors of sea star wasting: immune and microbial disruption during initial disease outbreak in southeast Alaska

Sea star wasting (SSW) disease has devastated sea star populations along the North American Pacific coast with some recovery since 2013. Though Vibrio pectenicida has recently been implicated as a causative agent, the dynamics of disease progression and host response in natural environments remain understudied. Here, we integrate transcriptomic and microbial data from wild Pycnopodia helianthoides sampled across sites affected and unaffected by SSW in southeast Alaska during the initial outbreak recorded in the region in 2016. Individuals exposed to SSW but lacking visible signs of disease showed elevated expression of complement system components, pathogen recognition and immune regulatory pathways relative to naive individuals. Differential expression of extracellular matrix and tissue remodelling genes suggests disruption of tissue homeostasis preceding visible signs of disease. Furthermore, network analyses revealed certain microbial abundances, including Vibrio spp., correlated with immune response and tissue integrity gene expression. Although V. pectenicida was detected in some samples, its rarity prevented detailed analysis. Nevertheless, higher prevalence in exposed samples is consistent with growing evidence implicating Vibrio infection as an agent of SSW. Together, our findings offer insight into early host-pathogen dynamics in wild populations, underscoring links between immune activation and microbial shifts with the onset of SSW disease.