Presently, one of the most widespread and virulent coral disease outbreaks on record is affecting the Florida Reef Tract (FRT), resulting in the mortality of thousands of colonies of at least 20 species of scleractinian coral, including the primary reef building species. First reported near Key Biscayne FL during 2014, this outbreak, recently described as “Scleractinian Tissue-Loss Disease” (TLD), progressed southward along the FRT and by December 2017 had reached the middle Florida Keys. In January 2018, we established experimental “sentinel” plots in the middle Florida Keys that were disease-free, but just south of affected areas, to monitor the disease’s spatial progression, assess size and species-specific disease susceptibility and progression rates, and evaluate its small-scale spatial epidemiology. We established two plots each at four locations ranging from 25m2 to 100m2 in area and in each, measured and mapped the location of each coral colony. In all, we identified and monitored more than 1,350 coral colonies representing 23 species. At two-week intervals, each colony was assessed for the presence of disease and, if diseased, estimated the percentage of the colony affected. TLD was first observed during February 2018 and by March was evident at all sites. Among those species that were sufficiently abundant, a species-specific pattern was evident. M. meandrites initially exhibited the highest prevalence, followed by Dichocoenia stokesii, Colpophyllia natans, and Pseudodiploria strigosa, then followed by Orbicella faveolata and Montastraea cavernosa. No size-specificity in the rate of disease occurrence was evident across the species examined. Additionally, preliminary analyses revealed that coral colonies were randomly distributed at seven of the eight experimental plots, but no intra- or inter-specific spatial patterns in disease progression were evident. We are currently refining this analysis to incorporate possible temporal dynamics, but presently it appears that the spatial dynamics of TLD is occurring at a scale larger than our experimental plots.

Currently, there is a widespread coral disease outbreak occurring on the reefs of Florida that has resulted in significant mortalities of 11 of the 24 species surveyed. This unprecedented outbreak provides a unique but time-sensitive opportunity to address critical questions about coral disease. This project examined potential etiological agents as well as putative probiotic microorganisms that could be used to treat or prevent infections. Transmission occurred during manipulative aquarium studies between diseased Montastraea cavernosa from the Fort Lauderdale area or Colpophyllia natans from the Keys and healthy fragments. Therefore, diseased fragments were treated with antibiotics to determine if a bacterial pathogen is involved. Disease progression was halted in 12 out of 13 diseased M. cavernosa fragments with a combinational amoxicillin/kanamycin treatment. Colpophyllia natans was less tolerant of combinational treatments while disease progression was comparatively faster with this species, however, treatment with nalidixic acid was able to slow or arrest disease progression in five out of eight fragments. Accordingly, bacteria were important for disease progression, so isolates from diseased M. cavernosa, C. natans, and Meandrina meandrites were tested for virulence during laboratory infection experiments. Various Vibrionaceae, Alteromonadales, and Rhodobacteraceae isolates are suspected to be pathogenic and are currently being investigated. In parallel to this work, bacterial isolates were cultured from fragments seemingly resistant to disease and then screened for antibacterial activity to isolate potential protective bacteria (probiotics). When one of these isolates, Pseudoalteromonas tunicata strain McH1#7, was inoculated onto diseased C. natans, disease progression was significantly slowed in three of six fragments. Subsequent NMR analysis of McH1#7 extracts identified the antibiotic korormicin while genome sequencing predicts the production of the antibacterials marinocine and tetrabromopyrrole. Further experiments are planned, which could potentially determine the etiological agent(s) responsible for this disease outbreak and potential biological controls for disease.

The Florida Reef Tract (FRT) spans approximately 595 km along the south and southeast Florida (SE FL) coastline from the Dry Tortugas to Martin County. These reefs continue to experience a devastating coral disease event that began in 2014 and altered the population demographics, effectively eliminating several species from certain locales. Southeast Florida reefs were hit first by the outbreak and have been classified as a coral disease endemic zone. In addition, Hurricane Irma caused substantial damage to SE FL reefs and further exacerbated impacts and changes in the coral population brought on by the disease. This talk presents the latest state of the SE FL coral population, and introduces intervention objectives and tools and methodologies, and evaluates the success of real-world in situ applications. Coral disease prevalence remained high after Hurricane Irma at 5.2% in the transects and 11.4% in the roving diver surveys with 15 diseased species surveyed from 62 sites. Irma impact prevalence ranged from 5.8% in the transects to 11.6% in the roving diver surveys. Most impacts were from sediment burial (49%) and dislodging (34%). Disease intervention was prioritized on the largest reef-building corals (> 2m diameter) in the region, predominantly Orbicella faveolata. Intervention entailed covering diseased tissue margins with chlorinated epoxy and creating trenches in the skeleton between diseased and healthy tissue and filling them with chlorinated epoxy. Treatments exhibited a 46.8% success rate at stopping the disease at the margin and a 58.6% success rate at stopping the disease from crossing the trench. Methods were most effective on O. faveolata (62%) and less effective on the limited number of treated M. cavernosa (52.2%) colonies. The number of new treatments on monitored corals spiked in June, were very low in July, increased in August and September, and were low in October. Treatment timing relates to rainy season and warmer temperature onset in May and the warmest periods in late summer. Ongoing work entails monthly monitoring and treatment on priority corals, field-testing antibiotic effectiveness, and collecting gametes to rear and grow into coral recruits in a lab setting.