Effects of temperature and light on the progression of black band disease on the reef coral, Montiporahispida

Understanding environmental drivers of black band disease (BBD), a virulent disease affecting corals worldwide, is critical to managing coral populations. Field monitoring studies have implicated seasonally elevated temperature and light as drivers of annual BBD outbreaks on the Great Barrier Reef, but do not distinguish their relative impacts. Here, we compare progression of BBD lesions on Montipora hispida among three controlled temperature (28.0, 29.0, 30.5°C) and two controlled light treatments (170, 440 μmol m⁻² s⁻¹) within normal seasonal ranges at the site. BBD progression rates were greatest (5.2 mm d⁻¹) in the 30.5°C/high-light treatment and least (3.2 mm d⁻¹) in the 28°C/low-light treatment. High light significantly enhanced BBD progression, whereas increases in disease progression under high temperatures were not statistically significant, identifying the greater role of light in driving BBD dynamics within the temperature range examined. Greater BBD progression during daytime compared with nighttime (by 2.2–3.6-fold across temperature and light treatments) corroborates our conclusion that light is the pre-eminent factor driving BBD progression at typical summer temperatures. Decreased photochemical efficiency of algal endosymbionts in the high-temperature/high-light treatments suggests that compromised health of the coral holobiont contributes to enhanced disease progression, highlighting the complexity of disease dynamics in host–pathogen systems responding to environmental changes.