Symbiodiniaceae Are the First Site of Heterotrophic Nitrogen Assimilation in Reef-Building Corals

Stephane Martinez, Renaud Grover, David M. Baker, Christine Ferrier-Pagès

Research output: Contribution to journalArticlepeer-review


Coral reefs depend on the highly optimized mutualistic relationship between corals and Symbiodiniaceae dinoflagellates. Both partners exchange nutrients obtained through heterotrophy of the host and autotrophy of the symbionts. While heterotrophy helps corals withstand the harmful effects of seawater warming, the exchange of heterotrophic nutrients between the two partners is poorly understood. Here, we used compound-specific δ 15N and δ 13C of amino acids (δ 15NAA and δ 13CAA) and a 15N pulse-chase experiment with Artemia salina nauplii in two coral-dinoflagellate associations to trace the assimilation and allocation of heterotrophic nutrients within the partners. We observed that changes in the trophic position (TPGlx-Phe), δ 15NAA, and δ 13CAA with heterotrophy were holobiont-dependent. Furthermore, while TPGlx-Phe and δ 15N of all AAs significantly increased with heterotrophy in the symbionts and host of Stylophora pistillata, only the δ 15NAA of the symbionts changed in Turbinaria reniformis. Together with the pulse-chase experiment, the results suggested a direct transfer of heterotrophically acquired AAs to the symbionts of S. pistillata and a transfer of ammonium to the symbionts of T. reniformis. Overall, we demonstrated that heterotrophy underpinned the nutrition of Symbiodinaceae and possibly influenced their stress tolerance under changing environmental conditions. IMPORTANCE Coral reefs rely upon the highly optimized nutritional symbiosis between corals and Symbiodiniaceae dinoflagellates. Heterotrophic feeding on plankton is key to the resistance of corals to environmental stress. Yet, a detailed understanding of heterotrophic nutrient assimilation and utilization within the symbiosis is lacking. Here, we used the advanced tools of compound-specific isotope analysis of amino acids and 15N-labeling of plankton to show that heterotrophy underpinned the nutrition of Symbiodinaceae. Symbionts received either heterotrophically acquired amino acids or recycled ammonium due to their association with the coral host. This study brought new insight into the nutrient exchanges in coral-Symbiodiniaceae associations and allowed a better understanding of the mechanisms involved in coral resistance to environmental stress.

Original languageEnglish
Issue number5
StatePublished - 26 Oct 2022
Externally publishedYes

Bibliographical note

Publisher Copyright:
Copyright © 2022 Martinez et al.


  • Symbiodiniaceae
  • compound-specific isotope analysis of amino acids
  • coral reefs
  • dinoflagellate
  • heterotrophy
  • nitrogen
  • pulse-chase
  • stable isotopes

ASJC Scopus subject areas

  • Microbiology
  • Virology


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