Variable Responses to a Marine Heat Wave in Five Fringing Reefs of Southern Taiwan

In 2020 marine heatwaves elicited severe bleaching on many of Earth's coral reefs. We compared coral reef benthic community composition before (April 2020), during (September 2020), and after (December 2020-September 2021) this event at five fringing reefs of Southern Taiwan. The four shallow (3 m) reefs were hard coral-dominated in April 2020 (cover = 37-55%), though non-bleached coral cover decreased to only 5-15% by December 2020. Coral abundance at the two shallow (3 m), natural reefs had failed to return to pre-bleaching levels by September 2021. In contrast, coral cover of two artificial reefs reached similar to 45-50% by this time, with only a small drop in diversity. This is despite the fact that one of these reefs, the Outlet, was characterized by temperatures >30 degrees C for over 80 days in a six-month period due not only to the bleaching event but also inundation with warm-water effluent from a nearby nuclear power plant. Only the lone deep (7 m) reef was spared from bleaching and maintained a coral/algal ratio >1 at all survey times; its coral cover actually increased over the 18-month monitoring period. These data suggest that (1) the natural deep reef could serve as a refuge from thermal impacts in Southern Taiwan, and (2) the remaining corals at the Outlet have either adapted or acclimatized to abnormally elevated temperatures.