Effectiveness of topical antibiotics in treating corals affected by Stony Coral Tissue Loss Disease

Abstract

Since 2014, Stony Coral Tissue Loss Disease (SCTLD) has led to mass mortality of the majority of hard coral species on the Florida Reef Tract. Following the successful treatment of SCTLD lesions on laboratory corals using water dosed with antibiotics, two topical pastes were developed as vehicles to directly apply antibiotic treatments to wild corals. These pastes were tested as placebos and with additions of amoxicillin on active SCTLD lesions on multiple coral species. The effectiveness of the pastes without antibiotics (placebo treatments) was 4% and 9%, no different from untreated controls. Adding amoxicillin to both pastes significantly increased effectiveness to 70% and 84%. Effectiveness with this method was seen across five different coral species, with success rates of the more effective paste ranging from 67% (Colpophyllia natans) to 90% (Orbicella faveolata and Montastraea cavernosa). Topical antibiotic application is a viable and effective tool for halting disease lesions on corals affected by SCTLD.

Disease Diagnostics and Potential Coinfections by Vibrio coralliilyticus During an Ongoing Coral Disease Outbreak in Florida

“…Furthermore, outside of the results of this study, there are no known intraspecific markers for more virulent lesions, which would be an important diagnostic for intervention efforts. Amoxicillin is used as a treatment for SCTLD in the field (Florida Keys National Marine Sanctuary, 2018;Neely et al, 2020), but coinfections by V. coralliilyticus, which is highly resistant to this antibiotic, may be problematic for mitigation efforts. Unfortunately, it is unclear what concentrations of amoxicillin V. coralliilyticus would experience in the field, so this statement is currently pure speculation.…”

“…Antibiotic resistance could prevent effective disease treatment, so resistance to antibiotics effective against SCTLD was a pertinent first test for these V. coralliilyticus isolates (Aeby et al, 2019;Neely et al, 2020). Antibiotic susceptibility tests were conducted in 96-well plates.…”

Evaluating the small-scale epidemiology of the stony-coral -tissue-loss-disease in the middle Florida Keys

“…We assessed model convergence using the Gelman-Rubin diagnostic [ 28 ] and by examining trace plots for each model parameter. Finally, we conducted a posterior-predictive check to assess goodness-of-fit by simulating replicated data under each fitted model and comparing summary statistics from the replicated data to those of the observed data [ 18 ]. We calculated goodness-of-fit statistics as the ratio of total predicted to total observed number of coral colonies in each of the three occupancy states, where Bayesian p-values < 0.05 and > 0.95 indicated lack of fit.…”

“…At present, the pathogen(s) responsible for SCTLD has not been identified, but a consortium of bacteria, most of which have been previously associated with other coral diseases, has been detected in association with SCTLD [ 17 ]. Moreover, the application of antibiotics to affected coral colonies, both in the laboratory and in the field, has been demonstrated to slow or stop the disease’s progression [ 18 ], further suggesting that bacterial pathogens are associated with SCTLD. Nevertheless, viral or eukaryotic cells may also be involved [ 19 ].…”

“…The severity of the SCTLD epidemic has resulted in what is perhaps an unprecedented concerted effort involving numerous researchers and resource managers throughout south Florida to coordinate a response and develop a management strategy to slow or prevent the spread of SCTLD [ 20 ]. A concerted effort is underway to identify and accurately diagnose the causative etiological agent(s) and its modes and rate of transmission, document its distribution and prevalence, identify any contributing environmental factors, and develop novel approaches to mitigating disease progression at the colony level [ 18 , 21 ]. An array of mitigation strategies has been proposed including treating coral colonies exhibiting signs of SCTLD through direct application of disinfectants, antibiotics, or probiotics, amputating the affected areas of diseased colonies, and targeting diseased or highly susceptible species for removal [ 22 ].…”