Transmissibility of Stony Coral Tissue Loss Disease (SCTLD) to Pacific Coral Species

Stony coral tissue loss disease (SCTLD) is a devastating coral disease first observed in 2014 near Virginia Key in Miami, Florida. It has since spread to 33 Caribbean countries and U.S. territories. However, it has yet to be observed in the Pacific. Prior studies have demonstrated the transmissibility of SCTLD via simulated ship ballast water, and the Panama Canal represents a potential avenue by which the disease could spread into the Pacific. It is therefore imperative to determine whether Pacific coral species are susceptible to SCTLD, and if so, to develop disease diagnostics. Two ex-situ waterborne disease experiments tested the susceptibility of the common eastern Pacific coral species, Pavona clavus, Pocillopora sp., and Porites lobata to SCTLD. Additionally, Orbicella faveolata and Acropora cervicornis were used as Atlantic susceptible and non-susceptible controls, respectively, to compare disease signs and susceptibility in Pacific species. Treatments included disease-exposed water (waterborne transmission), disease adjacent (near-contact transmission), and healthy coral-exposed water (no-disease control). Transmission data collected demonstrated that P. clavus and Pocillopora sp. are not immune to SCTLD, as some corals developed rapid tissue loss under near-contact and waterborne transmission. A survivorship analysis revealed that the susceptibilities of P. clavus and Pocillipora sp. to SCTLD could be similar to O. faveolata, a moderately-susceptible Atlantic species.. Tissue samples were collected and processed for 16S metabarcoding of microbial communities to assess variation among treatments and the presence of SCTLD indicator taxa. Sequencing results are forthcoming. Combined, these data provide a cellular and molecular diagnosis of SCTLD in P. clavus and Pocillopora sp., allowing the development of in-situ monitoring tools to evaluate the spread of disease in the Pacific Ocean. This information is critical for the management and prevention of SCTLD in coral reefs, providing further insight to the potential microbial origin of SCTLD, and developing SCTLD mitigation strategies across ocean basins.