High frequency temperature variability reduces the risk of coral bleaching

TLDR

Coral bleaching, the expulsion of algal symbionts from cnidarian hosts, mainly occurs under thermal stress and varies spatially at sub‑kilometer scales, making it unpredictable with conventional remote sensing. The study systematically evaluates how 20 in‑situ environmental variables and seven remotely sensed SST thermal stress metrics relate to 81 bleaching events across five major reef regions worldwide. The authors used in‑situ measurements of 20 environmental variables and seven remotely sensed SST thermal stress metrics to analyze 81 bleaching events across five major reef regions. High‑frequency temperature variability was the strongest predictor of bleaching, with each 1 °C increase in daily temperature range reducing severe bleaching odds by a factor of 33, indicating that reefs with greater variability could be key targets for conservation against warming.

Abstract

Coral bleaching is the detrimental expulsion of algal symbionts from their cnidarian hosts, and predominantly occurs when corals are exposed to thermal stress. The incidence and severity of bleaching is often spatially heterogeneous within reef-scales (<1 km), and is therefore not predictable using conventional remote sensing products. Here, we systematically assess the relationship between in situ measurements of 20 environmental variables, along with seven remotely sensed SST thermal stress metrics, and 81 observed bleaching events at coral reef locations spanning five major reef regions globally. We find that high-frequency temperature variability (i.e., daily temperature range) was the most influential factor in predicting bleaching prevalence and had a mitigating effect, such that a 1 °C increase in daily temperature range would reduce the odds of more severe bleaching by a factor of 33. Our findings suggest that reefs with greater high-frequency temperature variability may represent particularly important opportunities to conserve coral ecosystems against the major threat posed by warming ocean temperatures.