Commentary: Commentary on Reconstructing Four Centuries of Temperature-Induced Bleaching on the Great Barrier Reef by Hoegh-Guldberg et al. 2019 and DeCarlo 2020

• Published in: Frontiers in Marine Science 2020-10, Vol.7
• Main Authors: Kamenos, Nicholas A., Hennige, Sebastian J.
• Format: Article
• Language: English
• Subjects: acclimatization; adaptation; Archives & records; Barrier reefs; Bleaching; Calibration; coral; Coral reefs; Corals; Growth; Mortality; Physiology; Symbiodinaceae; Temperature
• ISSN: 2296-7745; 2296-7745
• DOI: 10.3389/fmars.2020.570620

Other studies acknowledged in KH18 (including Yu et al., 2006; Dishon et al., 2015) further demonstrate mass coral death events in the recent geologic record. [...]the concept of bleaching, or bleaching leading to mortality, before the observational record is already well-established in the peer-reviewed literature. Here we use further lines of evidence (Figure 1): it is known that coral band extension is positively related to temperature within physiological norms (e.g., Lough, 2008). [...]if extension was recording only growth responding to temperature within physiological norms, we would expect a positive relationship between temperature and extension (and therefore a negative relationship between temperature and extension-derived bleaching prevalence) (Figure 1A). A third trajectory also exists: if a reconstruction represented growth responding to thermal bleaching (low extension), we would expect a negative relationship between temperature and extension (and therefore a positive relationship between temperature and extension-derived bleaching prevalence, Figure 1C), as at higher temperatures there would be more corals exhibiting lower growth—this is the inverse of what would happen within physiological norms. Given (1) there is evidence in the literature of bleaching-related reductions in linear extension from several author groups (Leder et al., 1991; Suzuki et al., 2003; Cantin and Lough, 2014) and (2) the reconstructed bleaching data from KH18 matches the third hypothetical plot (Figures 1C,D), this supports our assertion that our proxy is reconstructing widespread thermal bleaching rather than bleaching driven by other, more localized, variables, or thermal growth within physiological norms.