Timing matters: survey timing during extended heat stress can influence perceptions of coral susceptibility to bleaching

Abstract

The frequency and duration of episodic ocean warming events are increasing, threatening the integrity of coral reefs globally. Interspecific differences in susceptibility to heat stress result from variable capacities of corals to resist bleaching or to persist in a bleached state. During shorter bleaching events, stress responses occur rapidly and the “window” for detecting bleaching is tightly constrained. However, during longer bleaching events, we argue that the timing of surveys can radically influence results, which need to be interpreted with care. For example, although “heat-resistant” corals may survive prolonged bleaching events, they have a greater chance of being recorded as having bleached because they can persist for longer in a bleached state. This could lead to erroneous conclusions about their vulnerability to heat stress compared with taxa that bleach and die rapidly. Therefore, as bleaching events lengthen, it is vital to consider not only temperature at the time of sampling, but also the accumulation of heat stress over the entire warming event. We present a simplified conceptual framework and an example from the Central Pacific to emphasize the importance of survey timing to perceived susceptibility of coral taxa to bleaching.