A gauge of coral physiology: re-examining temporal changes in <i>Endozoicomonas</i> abundance correlated with natural coral bleaching

Abstract

Bacteria contribute to many physiological functions of coral holobionts, including responses to bleaching. The bacterial genus, <i>Endozoicomonas</i>, 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 <i>Endozoicomonas</i> 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-<i>Endozoicomonas</i> association using multiple stony corals in natural environments. In this study, we monitored tissue color and microbiome changes in three coral species (<i>Montipora</i> sp., <i>Porites</i> sp., and <i>Stylophora pistillata</i>) in Kenting National Park, following the bleaching event. All tagged <i>Montipora</i> sp. and <i>Porites</i> sp. recovered from bleaching within 1 year, while high mortality occurred in <i>S. pistillata</i>. Microbiome analysis found no correlation of <i>Endozoicomonas</i> relative abundance and bleaching severity during the sampling period, but found a stronger correlation when the month in which bleaching occurred was excluded. Moreover, <i>Endozoicomonas</i> abundance increased during recovery months in <i>Montipora</i> sp. and <i>Porites</i> sp., whereas in <i>S. pistillata</i> it was nearly depleted. These results suggest that <i>Endozoicomonas</i> abundance may represent a gauge of coral health and reflect recovery of some corals from stress. Interestingly, even though different <i>Endozoicomonas</i> strains predominated in the three corals, these <i>Endozoicomonas</i> strains were also shared among coral taxa. Meanwhile, several <i>Endozoicomonas</i> strains showed secondary emergence during coral recovery, suggesting possible symbiont switching in <i>Endozoicomonas.</i> These findings indicate that it may be possible to introduce <i>Endozoicomonas</i> to non-native coral hosts as a coral probiotic.