Symbiodiniaceae phenotypic traits as bioindicators of acclimatization after coral transplantation

Coral-dinoflagellate symbiosis underpins coral reef resilience and influences conservation success, given the relationship's role in coral bleaching. Here, we transplanted Guam's dominant staghorn coral, Acropora pulchra, across four coral gardens and monitored their endosymbiotic dinoflagellates (family Symbiodiniaceae) for ∼15 months (May 2021-August 2022). Transplantation and predation resulted in temporary symbiotic destabilization, as signaled by increased cell roughness and decreased cell density. Eventually, the Symbiodiniaceae phenotypic profile mostly converged with the wild population, although cell density and red fluorescing photopigments remained modified. In March, corals paled, which allowed us to evaluate the Symbiodiniaceae assemblage's relationship with host color. Interestingly, cell density was not the most informative when predicting host color. Instead, fluorescence from antioxidant-associated pigments were most informative. We conclude that Symbiodiniaceae phenotypic traits respond differently depending on the condition, supporting their development as acclimatization bioindicators.