Diazotroph-Derived Nitrogen Assimilation Strategies Differ by Scleractinian Coral Species

Reef-building corals generally thrive in nutrient-poor tropical waters, where among other elements, nitrogen (N) availability often limits primary productivity. In addition to their close association with endosymbiotic dinoflagellates of the family Symbiodiniaceae, enabling an effective use and retention dissolved inorganic (DIN), scleractinian have developed strategies acquire new N: (1) They can ingest N-rich sediment particles preys (from picoplankton macro-zooplankton) via heterotrophy, including diazotrophs [plankton fixing dinitrogen (N 2 ) releasing part this nitrogen—Diazotroph-Derived N (DDN)—in seawater], a pathway called “heterotrophic nutrition on diazotrophs”; (2) Symbiotic located coral holobiont molecular machinery fix , “symbiotic fixation”. Here we used 15 isotopic labeling series incubations investigate relative contribution each these DDN transfer pathways three worldwide distributed species: Acropora muricata Galaxea fascicularis, Pocillopora damicornis . We show that provision fixation” is negligible compared obtained diazotrophs,” assimilation rates about thousand times lower for P. G. fascicularis or almost nil A. Through heterotrophic feeding planktonic diazotrophs, only successfully obtain fulfill large requirements (DDN asimilation rates: 0.111 ± 0.056 0.517 0.070 μg cm –2 h –1 respectively). Whereas again also largely consume likely benefit from ( Prochlorococcus Synechococcus cells; respectively, 2.56 1.57 10 4 2.70 1.66 cell ; 3.02 0.19 5 1.14 0.79 ). The present study confirms different dependencies tested species regarding appearing highly efficient at capturing plankton, while considered as mainly autotroph, does not rely food resources meet its energy needs.