However, SCTLD differs at the cellular level from other tissue loss diseases in that lesions consistently have lytic necrosis originating in the gastrodermis of the basal body wall ( Landsberg et al., 2020). Similar lesions have been found on corals throughout the world and are usually termed “white syndromes” ( Bourne et al., 2014). Lesions are described as focal or multifocal areas of acute or subacute progressive tissue loss. A case definition of the disease has been developed describing the visual appearance and histology of SCTLD ( Landsberg et al., 2020). The disease, termed stony coral tissue loss disease (SCTLD), affects over 24 species of hard corals and has resulted in extensive colony mortality ( Precht et al., 2016 Walton et al., 2018 Aeby et al., 2019 Sharp et al., 2020).
The Florida Reef Tract (FRT) is currently experiencing the most widespread, virulent, and longest running coral disease outbreak in recent history. Our study highlights that differences in coral mortality from SCTLD are not necessarily linked to host species, lesion morphology is reflective of subsequent rate of mortality, and disease dynamics change through time on reefs where the disease has newly emerged.
Aquaria studies found the rate of SCTLD transmission using lesions from the different zones (emergent and endemic) were similar. Lesion morphology on colonies was a significant predictor of amount of tissue loss. However, SCTLD dynamics changed, with year two tagged colonies showing declining disease prevalence, low mortality, and lesion morphology switched to a mixture of bleached polyps and tissue loss with or without bleached edges. In contrast, Lower Keys colonies tagged in the first year maintained 100% disease prevalence with high mortality, and disease lesions were predominantly tissue loss with no bleached edges. In both years, Fort Lauderdale colonies showed declining disease prevalence, low colony mortality, and disease lesions were mainly bleached spots lacking tissue loss. cavernosa SCTLD-affected colonies were followed for 2 years at one site in each region. siderea at Fort Lauderdale were dominated by smaller colonies (<5 cm) whereas larger colonies occurred in the Lower Keys. SCTLD prevalence was higher in the Lower Keys than at Fort Lauderdale and two of the common species, M. Reef surveys found sites in both regions had low coral cover, high algae cover, and similar coral species composition. Our objectives were to (1) assess the potential impact of SCTLD on overall reef condition by surveying reefs in each region, (2) in a single common species, Montastraea cavernosa, examine differences in SCTLD prevalence, colony mortality, and lesion morphology in each region, and (3) look for differences in contagion by conducting transmission experiments using lesions from each region. We examined two Florida sites with different temporal histories of disease emergence Fort Lauderdale where SCTLD is endemic and the Lower Florida Keys where SCTLD has recently emerged.
Stony coral tissue loss disease (SCTLD) is affecting corals across the Western Atlantic and displays species-specific and regional differences in prevalence, incidence, degree of mortality, and lesion morphology.
3Mote Marine Laboratory, Elizabeth Moore International Center for Coral Reef Research and Restoration, Summerland Key, FL, United States.2Department of Biology and Marine Biology, University of North Carolina Wilmington, Wilmington, NC, United States.1Smithsonian Marine Station, Fort Pierce, FL, United States.Greta Aeby 1*, Blake Ushijima 1,2, Erich Bartels 3, Cory Walter 3, Joseph Kuehl 3, Scott Jones 1 and Valerie J.