Specificity trumps flexibility—location-based stable associations between Symbiodiniaceae genera and Platygyra verweyi (Scleractinia; Merulinidae)

This study monitored symbiont communities bi-monthly in native coral cores used in a reciprocal transplantation of the coral Platygyra verweyi over two years (2014–2016) and samples of mother colonies from three locations with variable thermal regimes; our results show that associating with multiple Symbiodiniaceae genera (Cladocopium spp. and Durusdinium spp.) is not a prerequisite for symbiont shuffling. Platygyra verweyi associates with certain Symbiodiniaceae genera based on location. Results of quantitative real-time PCR indicated small-scale temporal changes in Symbiodiniaceae genera compositions from 2014 to 2016; however, these changes were not enough to invoke shuffling or switching, despite degree heating weeks exceeding 6 °C-weeks in 2014 and 4 °C-weeks in 2015, which usually resulted in substantial coral bleaching. Microsatellite analysis of the P. verweyi host showed no genetic differences among the study locations. Our results suggest that P. verweyi undergoes long-term acclimatization and/or adaptation based on microgeographic and local environmental conditionsby altering its combinations of associated Symbiodiniaceae. Results also suggest that shuffling might not be as common a phenomenon as it has been given credit for; corals thrive through specific associations, and many corals could still be vulnerable to climate change-induced stress, despite being promiscuous or able to associate with rare and background Symbiodiniaceae genera.