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

Abstract

Along the Florida reef tract, stony-coral-tissue-loss disease (SCTLD) has caused extensive mortality of more than 20 scleractinian coral species. The pathogen is unknown, but its epizoology indicates that the disease, facilitated by water currents, has progressed linearly along the tract, affecting reefs at the scale of hundreds of kilometers. To inform ongoing disease mitigation efforts, we examined the small-scale spatial and temporal epidemiology of SCTLD. We established a series of sites in the middle Florida Keys at offshore and inshore locations that had not yet shown signs of SCTLD. We then conducted high-frequency monitoring from February 2018 through September 2019 and documented the onset of SCTLD and its progression through the sites. SCTLD was first observed at one site during early February 2018 and by early March 2018 all sites showed signs of the disease. A dynamic multistate model suggested that disease transmission was independent of coral density and found little evidence of a positive association between a colony showing signs of SCTLD and the condition or distance to its neighboring colonies. The model did, however, indicate that the probability of a colony showing signs of SCTLD increased with increasing colony surface area. These results are consistent with the water-borne transmission of a pathogen that progressed rapidly through the survey area. However, by the end of our survey the progression of SCTLD had slowed, particularly at inshore sites. Many affected colonies no longer exhibited progressive tissue mortality typical of the disease, suggesting the existence of differentially resilient colonies or coral communities, meriting their use for future coral rescue and propagation and disease research. These results are useful for refining ongoing SCTLD mitigation strategies, particularly by determining when disease rates are sufficiently low for direct intervention efforts designed to arrest disease progression on individual coral colonies will be most effective.

Fine Scale Temporal and Spatial Dynamics of the Stony Coral Tissue Loss Disease Outbreak Within the Lower Florida Keys

“…Few new cases occurred during the summer months when thermal stress was highest and disease progression slowed considerably. A similar negative correlation was quantified between progression rates of SCTLD and DHW in St. Thomas, United States Virgin Islands (Meiling et al, 2020) and a decline in SCTLD activity coincided with increasing water temperatures in the Middle Keys in 2018, but not in 2019 (Sharp et al, 2020). Within the present study, there appeared to be a threshold at approximately 2-3 • C weeks (DHW) of accumulated thermal stress where the disease stopped progressing, and thus the diseased material in the coral tissue was no longer sloughing off into the water potentially transmitting to new corals as supported by the low incidence values.…”

“…Within the present study, there appeared to be a threshold at approximately 2-3 • C weeks (DHW) of accumulated thermal stress where the disease stopped progressing, and thus the diseased material in the coral tissue was no longer sloughing off into the water potentially transmitting to new corals as supported by the low incidence values. These findings could be the result of other seasonal environmental differences not studied here, however, our study and others (Meiling et al, 2020;Sharp et al, 2020) indicate that temperature may have an important influence on SCTLD dynamics. Furthermore, from our observations of physiological signs of stress (bleaching and/or paling) we did not find evidence of thermally stressed corals being more at risk to SCTLD.…”

“…In fact, Meiling et al (2020) showed a decrease in tissue loss rate associated with SCTLD as thermal stress accumulated prior to a bleaching event. Sharp et al (2020) also saw a decrease in SCTLD incidence and death rates during the 2018 coral bleaching season in the Middle Keys, but not during the 2019 coral bleaching season.…”

Failure to respond to a coral disease epizootic in Florida: causes and consequences

“…Note that total coral mortality data from Port Miami, highlighted in yellow, generally under-performs the regional average of SCTLD loss from all surveys highlighted in light brown. Also, note the consistency of SCTLD impacts by species across all sites irrespective of distance to Port Miami (Precht et al 2016;CSI 2016;DERM 2016;Gintert et al 2019;Hayes 2019;Sinigalliano et al 2019;Sharp et al 2020). (n = 7), coral bleaching (n = 4), competitive mortality (n = 6), and other factors (n = 9) accounted for the mortality of 8.8% of all monitored corals, yet 30.2% (n = 194) of all tagged corals likely died as a direct result of this disease outbreak .…”

Repeated ex situ Spawning in Two Highly Disease Susceptible Corals in the Family Meandrinidae

“…Coral rescue goals were to preserve genetic diversity in the Florida population before it was lost to SCTLD and to establish land-based gene banks for future repopulation efforts through translocation of fragments or sexually produced offspring from ex situ facilities to in situ coral nurseries or directly onto reefs. Sharp et al (2020) evaluated the epidemiology of SCTLD as it passed through the middle Florida Keys, identified the existence of intraspecific variability in disease resistance, and suggested that more resilient coral colonies or communities may merit inclusion in future rescue and propagation programs. Thus, future coral rescue efforts from SCTLD endemic areas may continue to occur.…”