Abstract

Since 2014. Florida's Coral Reef (FCR) has experienced a multi-year disease related mortality event. termed stony coral tissue loss disease (SCTLD). This disease affects over half of the reef building species in Florida. has high rates of mortality and follows a contagious model of transmission. Despite this. researchers have been unable to determine definitive pathogen(s) for this disease. Some studies have indicated that SCTLD lesion progression can be slowed down or halted on some coral species with a specially formulated ointment laced with amoxicillin. suggesting that the presumptive pathogen(s) for SCTLD may have a bacterial component. Here. we used 16S ribosomal RNA (rRNA) sequencing to identify key differences in the bacterial community of apparently healthy and SCTLD affected Montastraea cavernosa and Orbicella faveolata fragments. We also examined how the bacterial community changed over time (5%. 25%. 50%. and 75% progression of tissue loss) in each species. Overall. several bacterial taxa were repeatedly more abundant within diseased tissues compared with healthy tissue samples. In both species. orders Rhodobacterales. Rhizobiales. Desulfovibrionales and Clostridiales were found at higher relative abundances in disease samples compared to apparently healthy control samples. In M. cavernosa. the relative abundances of Clostridiales and Desulfovibrionales increased as the disease progressed. In O. faveolata. the relative abundance of Clostridiales increased as the disease progressed. and Chlamydiales were repeatedly more abundant in control O. faveolata. These results suggest that Rhodobacterales. Rhizobiales. Desulfovibrionales and Clostridiales may play a critical role in disease dynamics of SCTLD and future research should focus on identifying the function of these bacteria within diseased corals.

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