title: Major Sources of Organic Matter in a Complex Coral Reef Lagoon: Identification from Isotopic Signatures (δ13C and δ15N).
abstract: A wide investigation was conducted into the main organic matter (OM) sources supporting coral reef trophic networks in the lagoon of New Caledonia. Sampling included different reef locations (fringing, intermediate and barrier reef), different associated ecosystems (mangroves and seagrass beds) and rivers. In total, 30 taxa of macrophytes, plus pools of particulate and sedimentary OM (POM and SOM) were sampled. Isotopic signatures (C and N) of each OM sources was characterized and the composition of OM pools assessed. In addition, spatial and seasonal variations of reef OM sources were examined. Mangroves isotopic signatures were the most C-depleted (-30.17 ± 0.41 ‰) and seagrass signatures were the most C-enriched (-4.36 ± 0.72 ‰). Trichodesmium spp. had the most N-depleted signatures (-0.14 ± 0.03 ‰) whereas mangroves had the most N-enriched signatures (6.47 ± 0.41 ‰). The composition of POM and SOM varied along a coast-to-barrier reef gradient. River POM and marine POM contributed equally to coastal POM, whereas marine POM represented 90% of the POM on barrier reefs, compared to 10% river POM. The relative importance of river POM, marine POM and mangroves to the SOM pool decreased from fringing to barrier reefs. Conversely, the relative importance of seagrass, Trichodesmium spp. and macroalgae increased along this gradient. Overall, spatial fluctuations in POM and SOM were much greater than in primary producers. Seasonal fluctuations were low for all OM sources. Our results demonstrated that a large variety of OM sources sustain coral reefs, varying in their origin, composition and role and suggest that δ13C was a more useful fingerprint than δ15N in this endeavour. This study also suggested substantial OM exchanges and trophic connections between coral reefs and surrounding ecosystems. Finally, the importance of accounting for environmental characteristics at small temporal and spatial scales before drawing general patterns is highlighted.
authors.affiliation: Université de la Nouvelle-Calédonie, Laboratoire LIVE and LABEX « Corail », BP R4, 98851 Nouméa cedex, New Caledonia.
authors.forename: Marine J
authors.initials: MJ
authors.lastname: Briand
authors.affiliation: Centre d'Etudes Biologiques de Chizé, UMR 7372 CNRS-ULR, 79360 Villiers-en-bois, France.
authors.forename: Xavier
authors.initials: X
authors.lastname: Bonnet
authors.affiliation: Université de la Nouvelle-Calédonie, Laboratoire LIVE and LABEX « Corail », BP R4, 98851 Nouméa cedex, New Caledonia.
authors.forename: Claire
authors.initials: C
authors.lastname: Goiran
authors.affiliation: Université de La Rochelle, Département Littoral Environnement et Sociétés, UMR CNRS 7266 LIENSs, Bât. Marie Curie, Rue Olympe de Gouges, 17042 La Rochelle cedex 1, France.
authors.forename: Gaël
authors.initials: G
authors.lastname: Guillou
authors.affiliation: Université de la Nouvelle-Calédonie, Laboratoire LIVE and LABEX « Corail », BP R4, 98851 Nouméa cedex, New Caledonia.
authors.forename: Yves
authors.initials: Y
authors.lastname: Letourneur
mesh_terms: D001499:Bayes Theorem; D002247:Carbon Isotopes / Q000032:analysis*; D057894:Coral Reefs; D005843:Geography; D009510:New Caledonia; D009587:Nitrogen Isotopes / Q000032:analysis*; D045483:Rivers; D012621:Seasons; D012623:Seawater; D013696:Temperature
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes