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

William C Sharp,Colin P Shea,Erinn M Muller,John H Hunt,Kerry E Maxwell,Shashank Keshavmurthy

doi:10.1371/journal.pone.0241871

William C Sharp, Colin P Shea + Show 4 more

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https://doi.org/10.1371/journal.pone.0241871

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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.

Highlights

Disease can play a major role in structuring marine ecosystems and has been recognized as a driving force behind declines in reef-building corals worldwide leading to cascading effects throughout these ecosystems [1, 2]
The etiology of stony-coral-tissue-loss disease (SCTLD) remains unresolved, and our monitoring documented only tissue loss in coral colonies that was presumably related to SCTLD, the expression of the affected colonies we documented was largely consistent with the current case descriptions of its epidemiology [12, 13, 15, 30]
The disease transmission encompassed a wide range of species, with affected colonies typically exhibiting single or multifocal lesions of newly exposed, bright-white coral skeleton, indicating rapidly progressing tissue mortality but with clearly different susceptibilities to the disease among species, with species belonging to the families Meandrinidae and Faviidae being especially susceptible, commonly resulting in whole colony death

Summary

Introduction

Disease can play a major role in structuring marine ecosystems and has been recognized as a driving force behind declines in reef-building corals worldwide leading to cascading effects throughout these ecosystems [1, 2]. Assessing the potential modes of disease transmission can often prove challenging due to the complex etiologies of different coral diseases [8]. The (FRT) is experiencing the most widespread and virulent coral disease outbreak on record. This disease, termed stony-coral-tissue-loss disease (SCTLD), was first reported near Miami, FL, in 2014 [12], and by 2019 it had affected coral communities from the northernmost extent of the FRT to Key West, FL. The disease differs from previous diseases documented along the FRT by its unprecedented continuous–and multi-year–prevalence that has resulted in significant declines in the abundance of susceptible species on affected reefs which has likely altered ecosystem function [14]. The US Virgin Islands, the Turks and Caicos Islands, and Sint Eustatius [15, 16]

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