Stable Symbiodiniaceae composition in three coral species during the 2017 natural bleaching event in subtropical Hong Kong.

Adaptive changes in endosymbiotic Symbiodiniaceae communities have been reported during and after bleaching events in tropical coral species, but little is known about such shifts in subtropical species. Here we examined the Symbiodiniaceae communities in three coral species (Montipora peltiformis, Pavona decussata, and Platygyra carnosa) based on samples collected during and after the 2017 bleaching event in subtropical Hong Kong waters. In all of the collected samples, ITS2 meta-sequencing revealed that P. decussata and P. carnosa were predominantly associated with Cladocopium C1 and C1c, whereas M. peltiformis was mainly associated with two Cladocopium C21 types and C1. For each species, the predominant endosymbionts exhibited high fidelity, and the relatively low abundance ITS2-types showed minor changes between the bleached and recovered corals. Our study provided the first details of coral-algal association in Hong Kong waters, suggesting the selection of certain genotypes as a potential adaptive mechanism to the marginal environmental conditions.