Abstract

Climate change destabilizes the coral-Symbiodiniaceae symbiosis at a global scale, while the effects of anthropogenic environmental change on coral colonies have been extensively documented, other stages of the coral lifecycle have received less attention to date. Here, we examined photosynthesis and the assimilation of carbon and nitrogen in coral of the coral Pocillopora damicornis under acidification (1000 µatm) and elevated temperature (32℃) conditions and with a focus on nutrient cycling. Coral larvae maintained stable symbiont densities under all treatment conditions and showed no signs of bleaching or stress. Combined acidification and elevated temperature enhanced the net and gross photosynthesis of Symbiodiniaceae, and enhanced C:N ratios in the holobiont. However, this increase in carbon availability was predominantly reflected in increased carbon assimilation by Symbiodiniaceae with limited benefits for the host. overall, increase in Symbiodiniaceae productivity appear to be sufficient to maintain stable or enhanced carbon translocation to the host. This increase in autotrophic nutrient acquisition is likely central to maintaining the symbiosis under future climate change scenarios.

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