title: New insights into carbon acquisition and exchanges within the coral-dinoflagellate symbiosis under NH4+ and NO3- supply.
abstract: Anthropogenic nutrient enrichment affects the biogeochemical cycles and nutrient stoichiometry of coastal ecosystems and is often associated with coral reef decline. However, the mechanisms by which dissolved inorganic nutrients, and especially nitrogen forms (ammonium versus nitrate) can disturb the association between corals and their symbiotic algae are subject to controversial debate. Here, we investigated the coral response to varying N : P ratios, with nitrate or ammonium as a nitrogen source. We showed significant differences in the carbon acquisition by the symbionts and its allocation within the symbiosis according to nutrient abundance, type and stoichiometry. In particular, under low phosphate concentration (0.05 µM), a 3 µM nitrate enrichment induced a significant decrease in carbon fixation rate and low values of carbon translocation, compared with control conditions (N : P = 0.5 : 0.05), while these processes were significantly enhanced when nitrate was replaced by ammonium. A combined enrichment in ammonium and phosphorus (N : P = 3 : 1) induced a shift in nutrient allocation to the symbionts, at the detriment of the host. Altogether, these results shed light into the effect of nutrient enrichment on reef corals. More broadly, they improve our understanding of the consequences of nutrient loading on reef ecosystems, which is urgently required to refine risk management strategies.
authors.affiliation: Marine Department, Centre Scientifique de Monaco, 8 Quai Antoine Ier, MC-98000 Monaco, Principality of Monaco leila@centrescientifique.mc.
authors.forename: Leïla
authors.initials: L
authors.lastname: Ezzat
authors.affiliation: LEMAR - UMR 6539 UBO/CNRS/IRD, Institut Universitaire Européen de la Mer, Place Nicolas Copernic, Plouzané 29280, France.
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Maguer
authors.affiliation: Marine Department, Centre Scientifique de Monaco, 8 Quai Antoine Ier, MC-98000 Monaco, Principality of Monaco.
authors.forename: Renaud
authors.initials: R
authors.lastname: Grover
authors.affiliation: Marine Department, Centre Scientifique de Monaco, 8 Quai Antoine Ier, MC-98000 Monaco, Principality of Monaco ferrier@centrescientifique.mc.
authors.forename: Christine
authors.initials: C
authors.lastname: Ferrier-Pagès
mesh_terms: D064751:Ammonium Compounds / Q000378:metabolism; D000818:Animals; D037421:Anthozoa / Q000382:microbiology* / Q000502:physiology*; D002244:Carbon / Q000378:metabolism*; D004141:Dinoflagellida / Q000502:physiology*; D009566:Nitrates / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D010758:Phosphorus / Q000378:metabolism; D010788:Photosynthesis; D013559:Symbiosis
chemical_list: D064751:Ammonium Compounds; D009566:Nitrates; D010758:Phosphorus; D002244:Carbon; D009584:Nitrogen
keywords: 13C; autotrophy; coral