Coral-associated Symbiodiniaceae dynamics during the 2016 mass bleaching event in New Caledonia

The ecological success of shallow water corals hinges on their association with photosynthetic Symbiodiniaceae algae. This is affected by environmental drivers among which sea temperature is pivotal. In 2016, a prolonged heat wave challenged New Caledonia reefs triggering a severe bleaching event. Here, we tracked 72 coral colonies comprising two species of Pocillopora and Porites from a cross-shelf gradient during the event and subsequent recovery period. Symbiodiniaceae association over time was assessed using the ITS2 marker. Bleaching prevalence and photosynthetic efficiency showed that 83% of Pocillopora and 29% of Porites colonies were affected, with corals from a mid-shelf site having been most impacted. The majority of tracked colonies recovered by December 2016, with a recorded 33% mortality of Pocillopora, while Porites showed higher resilience. Consistent with previous studies, genotyping data suggest stable, species- and site-specific associations between corals and Symbiodiniaceae.