Physiological and reproductive repercussions of consecutive summer bleaching events of the threatened Caribbean coral Orbicella faveolata

Thermal stress is a major contributor to loss of coral cover, significantly impacting reefs during the third global bleaching event between 2014 and 2017. The long-term persistence of coral reefs depends on acclimatization and adaptation to changing climate, which are influenced greatly by the interactions between bleaching and reproductive success. We observed a genotypically diverse population of Orbicella faveolata before, during, and after consecutive bleaching events in 2014 and 2015 in the Florida Keys. We documented less bleaching during the second event despite 40% more time above local bleaching thresholds and an association between bleaching severity and subsequent spawning. Approximately 75% of colonies experienced the same or less severe bleaching in the second event despite being metabolically compromised, with a substantial minority (similar to 35%) faring better in the second event. The second bleaching event also resulted in smaller decreases in chlorophyll content per symbiont cell and symbiont-to-host cell ratio reef-wide, representing less damage to the coral-algal symbiosis. All colonies that recovered quickly (similar to 1 month) or did not bleach in 2014 released gametes in 2015, while only 60% of colonies that recovered more slowly did. Bleaching also impacted the amount of gametes released, with more severe bleaching significantly associated with gamete release from < 50% of the colony surface area. Bleaching and spawning outcomes were supported by dynamic physiological changes during bleaching and recovery. Lipid concentration and symbiont-to-host cell ratios collected from the bottom edge of the colony in the middle of the recovery period (February and April) were most important for predicting spawning the following year, highlighting the dynamic interaction between micro-habitats and time in recovery and gametogenesis. This study finds signals of physiological acclimatization in an important reef-building coral and underscores the importance of recovery post-bleaching and reproduction for the persistence of coral reefs.