Symbiodiniaceae assemblage shift during annual thermal stress in pillar coral

The 2014-2016 El Niño-Southern Oscillation (ENSO) phenomenon led to a recurrent thermal stress scenario, resulting in mass coral bleaching which detrimentally impacted coral reefs worldwide, including the Florida Reef Tract, during the summers of 2014 and 2015. This study targeted the rare and iconic pillar coral, Dendrogyra cylindrus, a slow-growing columnar species typically found in low abundance throughout its Caribbean range and contributed to further understanding the role of the algal symbionts in annually recurring hyper-thermal bleaching events.We showed that some cryptic Symbiodiniaceae members are not transient associates but persistent and ecologically relevant, especially during recurrent annual warming events as occurred on the Florida Reef Tract during the summers of 2014 and 2015. Additionally, we documented a rise in abundance of previously low abundance symbiont species associated strongly with bleaching resistance in the coral host during two consecutive hyper-thermal events.This ability to shuffle symbionts within the coral host may impart physiological resilience to rapid environmental change; and thus, represents a potentially important ecological process by which symbiotic corals acclimatize to changing ocean conditions.