Abstract
One of the latest threats to Florida’s Coral Reef is the stony coral tissue loss disease (SCTLD) outbreak which affects all but a few Caribbean scleractinian species and has spread throughout the Caribbean since 2014. Without a known pathogen, ecological studies of disease dynamics are essential for understanding SCTLD susceptibility at the individual colony and reef level. We investigated the epizootiology of the SCTLD outbreak in the lower Florida Keys at two spatial scales (among reefs ∼1 km and within reefs <10 m) over a 19 month period. In May 2018, three sites absent of SCTLD were established to characterize coral demographics (i.e., live tissue cover and colony diameter) along an offshore to nearshore gradient, and were subsequently surveyed for disease every 2–3 weeks until December 2019. SCTLD was first noted within the offshore and mid-channel reef sites in early October 2018 and later appeared at the nearshore site in early February 2019. SCTLD was negatively correlated with thermal stress, showing reduced progression and incidence rates after 2–3 weeks of water temperatures above the mean monthly maximum temperature for the region (i.e., 2–3 degree heating weeks). Although Pseudodiploria strigosa, Dichocoenia stokesii, Colpophyllia natans, and Diploria labyrinthiformis were the most susceptible species at our sites, areas with more Montastraea cavernosa and Orbicella faveolata colonies had higher prevalence and greater tissue loss associated with disease. The disease was more severe within quadrats with high species diversity, high coral cover, and disproportionately affected larger colonies. Our spatial analyses suggest that (1) SCTLD followed a contagious disease model within small (<10 m) spatial scales, (2) colonies within 1.5–3 m of a diseased coral were at higher risk for subsequently showing disease signs compared with those farther away, and (3) high incidence rates coincided with the loss of small scale (<10 m radius) spatial clustering, suggesting pulses of contagious spread on large spatial scales.
Highlights
Coral diseases have caused widespread deterioration of coral reefs over the last four decades (Porter et al, 2001; Sutherland et al, 2004); where, when, why, and how these outbreaks have occurred are largely unanswered questions (Shore and Caldwell, 2019)
Our study found that P. strigosa, D. stokesii, C. natans, and D. labyrinthiformis were the most susceptible species to stony coral tissue loss disease (SCTLD) and had the fastest progression rates, ∼ 14% of colony tissue lost per week
Muller et al (2020) showed significant clusters on the scale of tens of kilometers at annual time steps supporting the conclusion that SCTLD transmits at large spatial scales even over short periods of time
Summary
Coral diseases have caused widespread deterioration of coral reefs over the last four decades (Porter et al, 2001; Sutherland et al, 2004); where, when, why, and how these outbreaks have occurred are largely unanswered questions (Shore and Caldwell, 2019). Addressing these questions is essential for mitigating outbreaks, like one of the latest threats, the stony coral tissue loss disease (SCTLD). Investigations are hampered by limited capacity to rapidly and accurately diagnose the etiological agent(s) of SCTLD (Meyer et al, 2019; Rosales et al, 2020), a common issue within marine diseases in general (Burge et al, 2016) and coral disease diagnostics in particular (Ritchie, 2006)
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