Continuation of Microscopic and Microbial Insights into the Stony Coral Tissue Loss Disease (SCTLD) Outbreak Across Multiple Coral Species on Florida’s Coral Reef

Four integrated research tasks were performed using molecular biology, histology, and immunohistochemistry to provide insights into a possible mechanism of microbial infection that results in tissue loss, as well as potential pathogen(s) associated with stony coral tissue loss disease (SCTLD). For Task 1, molecular tools were used to characterize the endolithic communities of fungi, bacteria, and archaea from apparently healthy coral colonies, and affected and unaffected portions of diseased colonies sampled in 2016 and 2017. For Task 2, histological methods were used to characterize the endosymbiotic dinoflagellates in tissue from apparently healthy colonies and affected and unaffected portions of diseased colonies collected from Florida reefs or obtained following laboratory experiments conducted by Dr. Andrew Baker’s research team at the University of Miami to examine their role in the pathogenesis of SCTLD. For Task 3, immunohistochemistry was used to investigate the role of programmed cell death (PCD) vs. necrosis in SCTLD. For Task 4, histoslides of apparently healthy and SCTLD-affected coral tissue samples were digitized for online viewing. 

Results from Task 1 indicated that the combination of proteinase K and lysozyme incubations, with an additional DNA cleanup step, did not increase PCR amplification efficiency of MCAV samples for bacterial/archaeal analysis as desired. Results from Task 2 showed widespread necrosis and degradation within both SCTLD-exposed ‘healthy’ and ‘lesion’ samples. Results from Task 3 revealed that staining indicative of apoptosis was consistently observed in tissues of SCTLD-affected Pseudodiploria strigosa, Montastraea cavernosa, and Orbicella faveolata, indicating that this mode of cell death may be involved in SCTLD pathology. For task 4, histoslides were selected from 8 coral species examined by FWRI and scanned, uploaded, and linked through a spreadsheet by filename to enable viewing of the slides from the Florida Fish and Wildlife Conservation Commission’s website on SCTLD. These virtual slides will be used for further study and interpretation by histopathologists considering the results of all SCTLD research.