Commentary on Reconstructing four centuries of temperature-induced bleaching on the Great Barrier Reef by Hoegh- Guldberg et al 2019 and DeCarlo 2020

Mass coral bleaching events during the last 20 years have caused major concern over the future of coral reefs worldwide. Despite damage to these key ecological cornerstones, little is known about bleaching frequency prior to 1979 when regular modern systematic scientific observations began on the Great Barrier Reef (GBR). To understand the longer-term relevance of current bleaching trajectories, the likelihood of future coral acclimatization and adaptation, and thus persistence of corals, we reconstructed centennial length GBR bleaching records in Kamenos and Hennige (2018). We thank Hoegh-Guldberg et al. (2019) and DeCarlo (in press) (hereafter HG19 and DeC20, respectively) for considering our paper. HG19 and DeC20 question our approach; however here we demonstrate: 1) our use of ERSST data is during their most accurate and precise time period, 2) that linear extension is recording bleaching and that within and between-coral colony variability exists, necessitating a decadally binned approach, 3) that HG19 make errors in their dataset comparisons (also detected by DeC20), and 4) that HG19 and DeC20 use the observational data record beyond its power as it is not resolved by effort or species. Overall, we demonstrate the value of sclerochronological-type approaches over longer time-scales and the existing evidence of historic coral mortality, in contrary to Commentary assertions.