Metabolite pools of the reef building coralMontipora capitataare unaffected by Symbiodiniaceae community composition

Some reef corals form stable, dominant or codominant associations with multiple endosymbiotic dinoflagellate species (family Symbiodiniaceae). Given the immense genetic and physiological diversity within this family, Symbiodiniaceae community composition has the potential to impact the nutritional physiology and fitness of the cnidarian host and all associated symbionts. Here we assessed the impact of the symbiont community composition on the metabolome of the coralMontipora capitatain Kane'ohe Bay, Hawai'i, where different colonies can be dominated by stress-tolerantDurusdinium glynniior stress-sensitiveCladocopiumspp. Based on our existing knowledge of these symbiont taxa, we hypothesised that the metabolite profile ofD. glynnii-dominated corals would be consistent with poorer nutritional support of the host relative to those corals dominated byCladocopiumspp. However, comparative metabolite profiling revealed that the metabolite pools of the host and symbiont were unaffected by differences in the abundance of the two symbionts within the community. The abundance of the individual metabolites was the same in the host and in the endosymbiont regardless of whether the host was populated withD. glynniiorCladocopiumspp. These results suggest that coral-dinoflagellate symbioses have the potential to undergo physiological adjustments over time to accommodate differences in their resident symbionts. Such mechanisms may involve host heterotrophic compensation (increasing the level of nutrition generated by feeding relative to delivery from the algae), dynamic regulation of metabolic pathways when exchange of metabolites between the organisms differs, and/or modification of both the type and quantity of metabolites that are exchanged. We discuss these adjustments and the implications for the physiology and survival of reef corals under changing environmental regimes.