Environmental and biological drivers of white plague disease on shallow and mesophotic coral reefs

Abstract

Outbreaks of coral white plague (WP) disease have caused significant regional declines of reef-building Caribbean corals. Due to a greater availability of epidemiological data, studies have primarily focused on shallow coral reefs (< 30 m). In the U.S. Virgin Islands, however, WP disease prevalence appears to be higher on upper mesophotic (30–40 m) coral reefs when compared with shallow reefs and may be inhibiting coral recovery after environmental disturbances. The aim of this study was to investigate the relationship of environmental drivers with spatio-temporal patterns of WP prevalence across shallow and mesophotic coral reefs in the U.S. Virgin Islands. We recorded WP prevalence at 13 reef sites (five shallow, three mid-depth and five upper-mesophotic reefs) across the south shelf of St. Thomas approximately monthly between 2012 and 2015 using a drop camera method. The influence of environmental factors on disease prevalence was investigated using Bayesian inference with generalized linear mixed-effect models. We found that WP tended to increase during the beginning of the rainy season (June), and when levels of water turbidity and temperature were higher, and levels of oxygen and salinity lower. The disease prevalence was higher on mesophotic than on shallow or mid-depth reefs, probably due to higher availability of corals (host), and a possible temperature threshold for WP occurrence that allows long-term persistence (year-round) of the disease on upper-mesophotic reefs. This is the first study to implement the drop camera method to survey a coral disease over several reef sites and depths. This method can be applied on surveys of other rapid tissue loss diseases, such as the newly emergent stony-coral-tissue-loss-disease (SCTLD).