Abstract

Stony coral tissue loss disease (SCTLD) was first observed in St. Thomas. United States Virgin Islands in January of 2019. In merely one year. the disease spread to reefs around the entire island of St. Thomas and to the neighboring island of St. John. Due to the rapid progression of lesions on corals affected by SCTLD. the benthic communities at affected sites were significantly impacted. In the present study. we monitored permanent radial transects at multiple sites around St. Thomas and St. John in order to quantify disease prevalence among species through time and compare disease dynamics at sites with and without treatments (i.e.. antibiotic paste application. amputation. culling). Transects were established prior to SCTLD emerging at a site and then monitored at 1 week. 4 weeks. 6 weeks. 6 months. 1 year. and 1.5 years after first observations of SCTLD. At all sites. disease prevalence was highest approximately one month after initial observation of disease and declined through the remainder of the monitoring period. When all susceptible species were considered. there was no effect of treatment on disease prevalence nor incidence among sites. However. there was lower prevalence of diseased Orbicella spp. at treated sites than non-treated sites. likely because this is the most commonly treated species. This suggests that localized treatments can reduce disease pressure but the effect is species-specific. After only a few months of being affected by SCTLD. coral cover declined. and communities shifted to less diverse compositions. These results suggest intense treatment efforts are most valuable within the first month of disease at a site. Further research should investigate treatment techniques that have a range of impact beyond a single lesion to reduce effort required to preserve maximum coral diversity.

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