Coral Bleaching Response: Implications From Alcohol Biomarkers

Coral bleaching is one of the most serious threats to coral reef ecosystem. With the rapid rise of temperature and the continuous intensification of human activities, more and more attention has been paid to the physiological and ecological response and resilience of coral bleaching. In this study, we studied Goniastrea minuta and Galaxea fascicularis, and analyzed the content, δ¹³C composition and its abundance characteristics of alcohol biomarkers (n-alkanols and steroid) between healthy and bleaching corals, revealed the variation process of organic matter sources and flux before and after coral bleaching, and elucidated the recovery mode and ability of leaching corals. The results showed that in healthy G. minuta and G. fascicularis, the proportion of C_16-18 n-alkanols was the highest (79.7% and 79.8%, respectively), and the δ¹³C value biased towards positive (mean −17.6‰ and −18.9‰). indicating that C_16-18 was mainly derived from the zooxantheliumfascicularis and transferred to the coral host in autotrophic form. The steroid molecules and δ¹³C composition were basically consistent, reflecting thesimilar zooxanthellic group structure between the two. After bleaching, the content and proportion of n-alkanols in C_16-18 decreased significantly, while those in C_22-28 demonstrated an opposite upward trend, indicating an increase in contribution of terrigenous organic matter. The steroid content decreased, but the amplitude varied, and the compositions changed significantly. The δ¹³C steroid composition showed a negative bias, suggesting the presence of heterotrophic organic matter input. This study has shown that G. minuta and G. fascicularis are mainly focused on heterotrophic recovery, but the overall recovery rate is slower or less efficient, which may be related to both the oligotrophic environment and the lack of adequate food sources in reef area. In addition, the C_31-35 ketone compounds was detected in bleaching corals, which is inferred to be the product of human activities (biomass burning), anthropogenic pollution combined with climate change may exacerbate the coral bleaching.