These files contain data and scripts supporting all results reported in Graham et al. paper, "Does the seagrass microbiome mediate risk of disease?". In Graham et al., we found: Microbial communities strongly influence the health and functions of their hosts and can be a first line of defense against infections. While research increasingly shows a role of the microbiome in terrestrial plant disease resistance, this has yet to be demonstrated with the diversity of pathogens infecting marine plants. Here, we test the hypothesis that the host-associated microbiome increases host resistance to seagrass wasting disease. We experimentally manipulated the eelgrass (Zostera marina) microbiome with antibiotics, mechanical removal by vortexing, and dilute bleach, then inoculated plants with Labyrinthula zosterae (Lz), the causative agent of seagrass wasting disease. Our experiments using different microbiome disruption methods consistently showed significantly higher disease severity in eelgrass with an unmanipulated microbiome. Indeed, our results did not support a protective role of the eelgrass microbiome against Lz. We paired these experiments with 16S rRNA gene sequencing of field-collected eelgrass to determine how microbial communities may change in different disease states. Microbial composition and richness between diseased and healthy (completely asymptomatic) tissue varied markedly in one of three sampling years, suggesting diseased eelgrass could have a degradation community under certain conditions. This work enhances our understanding of plant-microbe-pathogen interactions in a valuable marine foundation species.