Abstract
A deadly coral disease outbreak has been devastating the Florida Reef Tract since 2014. This disease, stony coral tissue loss disease (SCTLD), affects at least 22 coral species causing the progressive destruction of tissue. The etiological agents responsible for SCTLD are unidentified, but pathogenic bacteria are suspected. Virulence screens of 400 isolates identified four potentially pathogenic strains of Vibrio spp. subsequently identified as V. coralliilyticus. Strains of this species are known coral pathogens; however, cultures were unable to consistently elicit tissue loss, suggesting an opportunistic role. Using an improved immunoassay, the VcpA RapidTest, a toxic zinc-metalloprotease produced by V. coralliilyticus was detected on 22.3% of diseased Montastraea cavernosa (n = 67) and 23.5% of diseased Orbicella faveolata (n = 24). VcpA+ corals had significantly higher mortality rates and faster disease progression. For VcpA– fragments, 21.6% and 33.3% of M. cavernosa and O. faveolata, respectively, died within 21 d of observation, while 100% of similarly sized VcpA+ fragments of both species died during the same period. Further physiological and genomic analysis found no apparent differences between the Atlantic V. coralliilyticus strains cultured here and pathogens from the Indo-Pacific but highlighted the diversity among strains and their immense genetic potential. In all, V. coralliilyticus may be causing coinfections that exacerbate existing SCTLD lesions, which could contribute to the intraspecific differences observed between colonies. This study describes potential coinfections contributing to SCTLD virulence as well as diagnostic tools capable of tracking the pathogen involved, which are important contributions to the management and understanding of SCTLD.
Highlights
Coral reefs currently face a variety of threats, including anthropogenic climate change, pollution, overfishing, and disease
Pathogenic Vibrios From Infected Corals Identified as V. coralliilyticus
The bacterial isolates were organized into 80 groups each consisting of 5 isolates, of which, 8 groups elicited tissue loss or bleaching when screened against healthy corals
Summary
Coral reefs currently face a variety of threats, including anthropogenic climate change, pollution, overfishing, and disease These threats and documented coral disease outbreaks have increased over time, further damaging important reef ecosystems (Harvell et al, 1999; Porter et al, 2001; Bruno et al, 2007; Maynard et al, 2015). This outbreak has been ongoing since late 2014, where it was first observed in Florida around Miami-Dade county (Precht et al, 2016) This highly virulent disease has since spread north and south along almost the entirety of the Florida Reef Tract at a rate of approximately 100 m per day (Florida Keys National Marine Sanctuary, 2018; Muller et al, 2020). The reason behind these differences, along with intraspecific variability between lesion progression rates and presentation, are currently unknown
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