Symbiodiniaceae Community Structure and Thermal Tolerance in Soft Corals from Captive Aquarium Environments

Corals in aquarium systems experience environmental conditions that differ substantially from those in the wild, potentially altering their microbiomes and influencing health and stress resilience. In this study, we investigated shifts in symbiotic dinoflagellates (family Symbiodiniaceae) in common soft corals sourced from aquarium stores across Southern California. Using ITS2 amplicon sequencing, we characterized symbiont communities across coral genera and store locations. We then conducted a high heat pulse assay on a subset of samples to examine relationships between thermal tolerance, symbiont community composition, coral genus, and source location. We found that Symbiodiniaceae communities were highly similar among corals within shared aquarium store environments, rather than exhibiting genus-specific symbiont profiles, and most corals had Cladocopium-dominated symbiont communities. Thermal tolerance varied strongly among coral genera, with Briareum (green star polyps) displaying the highest heat tolerance. These findings suggest that captive aquarium environments can structure coral symbiont communities across distantly related hosts although the coral host strongly influences physiological responses to heat stress. Understanding how artificial environments shape coral holobionts is relevant not only for the aquarium trade but also for coral husbandry in research and conservation, where symbiont composition can influence survival and experimental outcomes.