Meeting Abstract
In July 2016, the East Bank of the Flower Garden Banks (FGB) National Marine Sanctuary experienced a localized mortality event (LME) of multiple invertebrate species that caused unprecedented reductions in coral cover for the reef. Abiotic data collected after the LME suggest that hypoxia driven by freshwater run-off and stratification contributed to the mortality. Yet, little is known about the molecular responses of corals to low oxygen. Gene expression samples from affected and unaffected coral colonies revealed physiological consequences of the event on the coral host and its algal symbiont from two congeneric coral species (Orbicella franksi and Orbicella faveolata) from both East (affected) and West (unaffected) Banks. Affected colonies differentially regulated genes involved in mitochondrial components and oxidative stress, suggesting a response to hypoxia. To test this hypothesis, we measured coral host and algal gene expression in response to experimentally induced low dissolved oxygen (control = 6.9 ± 0.08 mg/L, hypoxic = 0.083 ± 0.017 mg/L) in replicate fragments of three healthy O. faveolata colonies from the FGB. This controlled experiment also revealed differential regulation of mitochondrial components and oxidative stress response mechanisms. The delta ranks of enriched gene ontology terms were significantly positively correlated between the responses to the natural LME and in response to the controlled hypoxic challenge, providing further support that hypoxia contributed to the LME at FGB. These in situ and experimental data highlight the diagnostic power of an affordable sequencing methodology using ecological samples. Furthermore, our results shed light on the molecular responses of corals to hypoxia.
