Meeting Abstract
Coral reefs are experiencing global declines as climate change and other stressors cause environmental conditions to exceed the physiological tolerances of host organisms and their microbial symbionts (collectively termed the holobiont). To assess the role of symbiont community composition in holobiont stress tolerance, diversity metrics and abundances of dinoflagellate endosymbionts were quantified from eight Acropora millepora coral colonies (genets) that thrived under or responded poorly to various stressors. Four best performer coral genets were selected for analysis because they survived 10 days of high temperature, high pCO2, bacterial addition, or combined stressors, whereas four worst performer genets were analyzed because they experienced significant mortality under these stressors. Seven of eight genets mainly hosted Cladocopium symbionts, but also contained Symbiodinium, Brevolium, and/or Durusdinium symbionts at lower abundances. Control fragments of each genet ultimately identified as best performing had low symbiont alpha and beta diversity, whereas the worst genets had higher alpha and beta diversity. After 10 days of stress, symbiont communities in worst performers had a greater proportional increase in symbiont variability (relative to control fragments) than did the best performers, with bacteria and heat treatments causing the most drastic changes in symbiont communities. These findings emphasize that community diversity metrics may be important indicators of resilience in hosts central to diverse disciplines, from agriculture to medicine.
