Stony coral tissue loss disease has spread widely in the Caribbean and causes substantial changes to coral community composition because of its broad host range and high fatality rate. To reduce SCTLD impacts, intervention programs throughout the region have divers treating corals with antibiotics. We assessed the effect of antibiotic treatment in the British Virgin Islands by comparing coral communities at 13 treated sites to those at 13 untreated sites. The prevalence of white syndromes (assumed to be primarily SCTLD), the severity of white syndrome lesions, partial colony mortality and complete colony mortality all showed a pattern consistent with benefits of treatment: they were reduced at treated sites but only for species of medium- and high-susceptibility to SCTLD. In contrast, the prevalence and severity of lesions from other diseases, and other causes of tissue loss, were all unrelated to treatment. Re-ordering of rank abundance at the community-level was also consistent with a positive effect of treatment because rare, highly SCTLD-susceptible species increased slightly in relative cover at treated sites. Although there was limited statistical support for these responses individually, collectively the overall pattern of results indicates a modest beneficial effect of the intervention program. Diver-based intervention programs using antibiotics are thus a viable part of management plans for STLD at the epidemic stage.

We surveyed each site on SCUBA using haphazardly placed 30-m transects. All scleractinian coral colonies intersected by the transect tapes that were > 10 cm in maximum linear dimension were identified to species and recorded.