Coral larvae have unique transcriptomic responses to pathogenic and probiotic bacteria

Abstract The growing prevalence of coral disease and other stressors threatens coral reefs, and evidence suggests these stressors not only affect adult corals but may also have impacts on early life stages. Yet, our understanding of coral larval physiology, including immunological function, is significantly limited. Here, we leverage the temperate coral experimental system Astrangia poculata to investigate the transcript-level response of A. poculata to exposure to pathogenic and probiotic bacteria. The bacteria tested in the experiment were the known coral pathogen ( Vibrio coralliilyticus RE22) and a probiont ( Phaeobacter inhibens S4) previously demonstrated to inhibit the pathogen’s growth. In this study, we aim to (1) characterize the general immune response of A. poculata larvae to bacterial stimuli, (2) identify defense mechanisms that may aid in host resistance to pathogens, and (3) characterize the impacts of probiont exposure on A. poculata larval gene expression. Our data identify both shared and divergent larval immune responses to probiotic and pathogenic bacteria. Immunological peptidases were enriched in response to bacteria—expression of endopeptidases increased in response to probiont and pathogen, and metallopeptidase activity was enriched in response to the pathogen. Clustering analyses further revealed a diverse array of immune components in response to the pathogen, while its response to the probiont was associated with a broad range of developmental and metabolic terms. Collectively, the data from this study identify immune components that may play a role in coral response to bacteria during their early life stages, with broad relevance to current restoration and conservation approaches.