Meeting Abstract
Reduction of dissolved oxygen (DO) in ocean surface waters is a consequence of both local (eutrophication) and global (ocean warming) stressors. Recently, acute conditions of low DO have been linked to mass mortality events on coral reefs. Few studies have investigated the impact of low DO events on coral microbiomes, which are important in coral health and tolerance to environmental stress. We present one of the first studies to examine coral microbiome responses to low DO, coupling field and lab results. In July 2016, benthic organisms on reefs at the Flower Garden Banks National Marine Sanctuary (FGBNMS, northwest Gulf of Mexico) experienced a Localized Mortality Event (LME), which was linked to encroachment of storm-generated floodwaters, up-welling, and low DO. We collected healthy and dying corals (Orbicella faveolata) and other dying organisms at the FGBNMS during the LME and during the next corresponding season with ‘normal’ conditions (approximately two years after the LME). Many abiotic and biotic factors change when floodwaters interact with reef environments, making it difficult to disentangle the effects of low DO from co-occurring stressors. To further examine the immediate responses of O. faveolata to low DO in the absence of other stressors, we experimentally reduced DO directly (bubbling with N2 gas) and indirectly (limiting gas exchange with the atmosphere). We then characterized coral-associated bacterial communities from field and experimental samples, and compared the long-term response of corals collected from the FGBNMS to the short-term response seen in experiments. A better understanding of the resiliency of reef-building corals to low DO is important given the significant threat of ocean deoxygenation.
