Corals are mixotrophs: they are able to fix inorganic carbon through the activity of their symbiotic dinoflagellates and to gain nitrogen from predation on plankton and uptake of dissolved organic and inorganic nutrients. They also live in close association with diverse diazotrophic communities, inhabiting their skeleton, tissue and mucus layer, which are able to fix dinitrogen (N2). The quantity of fixed N2 transferred to the corals and its distribution within coral compartments as well as the quantity of nitrogen assimilated through the ingestion of planktonic diazotrophs are still unknown. Here, we quantified nitrogen assimilation via (i) N2 fixation by symbiont diazotrophs, (ii) ingestion of cultured unicellular diazotrophs and (iii) ingestion of natural planktonic diazotrophs. We estimate that the ingestion of diazotrophs provides 0.76±0.15 µg N cm−2 h−1, suggesting that diazotrophs represent a non-negligible source of nitrogen for scleractinian corals.
The authors declare no competing or financial interests.
Conceived and designed the experiments: M.B., F.H., S.B. and A.L. Performed the experiments: F.H., M.C. and M.B. Analysed the data: M.B. and M.C. Contributed reagents/materials/analysis tools: F.H., A.L. and O.G. Wrote the paper: M.B. and F.H., with comments and suggestions from all authors.
This work was funded by the LabEx-Corail DIADOM project (postdoctoral fellowship to M.C.), the LabEx-Corail COCAUNUT project and the Agence Nationale de la Recherche (ANR starting grant VAHINE ANR-13-JS06-0002) to S.B. M.B. was funded by the People Programme (Marie Skłodowska-Curie Actions) of the European Union's Seventh Framework Programme (FP7/2007-2013) under Research Executive Agency (REA) grant agreement no. 625185. A.L., S.B. and F.H. were funded by the Institut de Recherche pour le Développement (IRD).
- Received February 22, 2016.
- Accepted June 14, 2016.
- © 2016. Published by The Company of Biologists Ltd