Award: OCE-1516411

In summer of 2014 and again in 2015, a coral bleaching event associated with anomalously warm seawater temperatures severely impacted elkhorn coral in the Florida Keys (USA). Water temperatures on the reef reached 1 degree Celsius above typical summer temperatures for several weeks at these reef sites. Surveys of this threatened coral documented a range of bleaching responses; colonies ranged from fully bleached (solid white) to partly bleached, to apparently unaffected. Bleaching response varied between reefs but also within single, monoclonal stands of A. palmata and even within a single colony. The variability in bleaching response could not be completely explained by apparent environmental differences (temperature and light) nor host genotype. This project aimed to explore the role of coral symbionts in the hostÆs bleaching susceptibility by sampling elkhorn coral tissue documented to exhibit a range of bleaching responses. Further, the consecutive thermal stress events provided an opportunity to evaluate potential acclimatization in this coral. Micro-tissue samples were collected in 2014 and 2015 from monitored elkhorn coral colonies with documented bleaching response during thermal stress events. In most cases multiple samples were collected from different parts of the same colony to evaluate within-colony scale variability. In an ongoing component of this project, these samples are being analyzed to identify the genotype of both host and zooxanthellae, and compare the microbiome across samples to identify any correlation with bleaching response both within and between colonies. Understanding the variable bleaching response in elkhorn coral may reveal stands that are more resilient to bleaching which could improve management and propagation success of this threatened species. Last Modified: 03/30/2016 Submitted by: Dana E Williams