A gauge of coral physiology: re-examining temporal changes in abundance correlated with natural coral bleaching.

Bacteria contribute to many physiological functions of coral holobionts, including responses to bleaching. The bacterial genus, , dominates the microbial flora of many coral species and its abundance appears to be correlated with coral bleaching. However, evidences for decoupling of bleaching and abundance changes have also been reported. In 2020, a severe bleaching event was recorded at reefs in Taiwan, providing a unique opportunity to re-examine bleaching- association using multiple stony corals in natural environments. In this study, we monitored tissue color and microbiome changes in three coral species ( sp., sp., and ) in Kenting National Park, following the bleaching event. All tagged sp. and sp. recovered from bleaching within 1 year, while high mortality occurred in . Microbiome analysis found no correlation of relative abundance and bleaching severity during the sampling period, but found a stronger correlation when the month in which bleaching occurred was excluded. Moreover, abundance increased during recovery months in sp. and sp., whereas in it was nearly depleted. These results suggest that abundance may represent a gauge of coral health and reflect recovery of some corals from stress. Interestingly, even though different strains predominated in the three corals, these strains were also shared among coral taxa. Meanwhile, several strains showed secondary emergence during coral recovery, suggesting possible symbiont switching in These findings indicate that it may be possible to introduce to non-native coral hosts as a coral probiotic.