Coral communities in the Caribbean face a new and deadly threat in the form of the highly virulent multi-host stony coral tissue loss disease (SCTLD). In late January of 2019, a disease with signs and characteristics matching that of SCTLD was found affecting a reef off the coast of St. Thomas in the U.S. Virgin Islands (USVI). Identification of its emergence in the USVI provided the opportunity to document the initial evolution of its spatial distribution, coral species susceptibility characteristics, and its comparative impact on coral cover at affected and unaffected coral reef locations. Re-assessments at sentinel sites and long-term monitoring locations were used to track the spread of the disease, assess species affected, and quantify its impact. The disease was initially limited to the southwest of St. Thomas for several months, then spread around the island and to the neighboring island of St. John to the east. Differences in disease prevalence among species were similar to reports of SCTLD from other regions. Highly affected species included Colpophyllia natans, Eusmilia fastigiata, Montastraea cavernosa, Orbicella spp., and Pseudodiploria strigosa. Dendrogyra cylindrus and Meandrina meandrites were also highly affected but showed more variability in disease prevalence, likely due to initial low abundances and the rapid loss of colonies due to disease. Siderastrea spp. were less affected and showed lower prevalence. Species previously reported as unaffected or data deficient that were found to be affected by SCTLD included Agaricia spp., Madracis spp., and Mycetophyllia spp. We also observed multi-focal lesions at SCTLD-affected sites on colonies of Porites astreoides, despite that poritids have previously been considered low or not susceptible to SCTLD. Loss of coral cover due to acute tissue loss diseases, which were predominantly SCTLD, was significant at several monitoring locations and was more impactful than previous mass bleaching events at some sites. There are no signs that the USVI SCTLD outbreak is abating, therefore it is likely that this disease will become widespread across the U.S. Caribbean and British Virgin Islands in the near future.

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Many studies have evaluated the impacts of hurricanes on coral communities, but far less is known about impacts, recovery, and resilience of sponge communities to these extreme events. In September 2017, St. Thomas, U.S. Virgin Islands, was impacted by two Category 5 hurricanes within 2 weeks: Hurricanes Irma and Maria. Such extreme events occurring in such rapid succession are virtually unprecedented. Pre-hurricane (2015Pre-hurricane ( , 2016 surveys of permanent transects at six sites around St. Thomas were compared with those at 10 weeks post-hurricanes (December 2017) to evaluate storm impacts on sponges and on benthic coral reef constituents. These surveys also established a baseline for evaluating future recovery. Percent cover of sponges declined by 24.9% post-hurricanes. In contrast, sponge density increased by 43.9% from 2015 to 2016 and declined slightly after the hurricanes. Overall sponge volume did not vary over time, and whereas sponge diversity was similar in 2015 and 2016, it increased post-hurricanes. Sponge morphologies were differentially affected by the hurricanes; the proportion of upright sponges declined by 36.9%, while there was a 24.4% increase in encrusting sponges. Coral and macroalgal cover did not change significantly over the sampling period, while percent cover of epilithic algae increased and non-living substrata decreased from 2015 to 2016 but did not change further post-hurricanes. At all sites, recruitment and/or regrowth of sponges was observed within 10 weeks post-hurricanes, indicating potential resilience in Caribbean sponge communities. Whether these sponge communities return to pre-hurricane conditions and how long that will take remains to be seen.

It is suspected that land cover alteration on the southern coast of St. Thomas, USVI has increased runoff, degrading nearshore water quality and coral reef health. Chronic and acute changes in water quality, sediment deposition, and coral health metrics were assessed in three zones based upon perceived degree of human influence. Chlorophyll (p<0.0001) and turbidity (p=0.0113) were significantly higher in nearshore zones and in the high impact zone during heavy precipitation. Net sediment deposition and terrigenous content increased in nearshore zones during periods of greater precipitation and port activity. Macroalgae overgrowth significantly increased along a gradient of decreasing water quality (p<0.0001). Coral bleaching in all zones peaked in November with a regional thermal stress event (p<0.0001). However, mean bleaching prevalence was significantly greater in the most impacted zone compared to the offshore zone (p=0.0396), suggesting a link between declining water quality and bleaching severity.