Net and gross incorporation of nitrogen by marine copepods fed on N-labelled diatoms: Methodology and trophic studies |
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Authors: | Dorothée Vincent Gerd Slawyk Géraldine Sarthou Laurent Seuront Benoît Sautour |
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Affiliation: | a Maison de la Recherche en Environnement Naturel (MREN), FRE CNRS 2816 ELICO, Université du Littoral Côte d'Opale (ULCO), 32 avenue Foch, 62 930 Wimereux, France b Laboratoire d'Océanographie et de Biogéochimie (LOB), UMR CNRS 6535, Campus de Luminy, case 901, 13 288 Marseille cedex 9, France c Laboratoire de Chimie Marine, UMR CNRS/UPMC 7144, and UBO, BP 74, 29 682 Roscoff cedex, France d LEMAR/UMR 6539/IUEM, Technopole Brest Iroise, Place Nicolas Copernic, 29 280 Plouzané, France e Station Marine de Wimereux, FRE CNRS 2816 ELICO, Université des Sciences et Technologies de Lille (USTL), 28 avenue Foch, 62 930 Wimereux, France f School of Biological Sciences, Flinders University, GPO Box 2100, Adelaide SA 5001, South Australia, Australia g Laboratoire d'Océanographie Biologique, UMR 5805 EPOC, 2, rue du Pr. Jolyet, 33 120 Arcachon, France |
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Abstract: | The stable isotope of nitrogen (15N) and an appropriate three-compartment model were used in two 24-h lasting feeding experiments to trace the flow of N through the copepod Acartia discaudata and Calanus helgolandicus fed on 15N-labelled Skeletonema costatum and Thalassiosira weissflogii, respectively. Details of the labelling technique and principles of the computation of N transport rates are given. At the end of a single 24-h feeding period only about one third of the total amount of N ingested by A. discaudata was incorporated into the copepod's body N; we refer to this rate as net incorporation. Most of the N ingested was lost as ammonium (48% of total N ingested), followed by losses in the form of eggs + fecal pellets (13%) and dissolved organic N (DON, 9%). The sum of net incorporation and the latter losses is defined as gross incorporation. Net incorporation by C. helgolandicus and N losses did not vary over time during a 24 h lasting time-series feeding experiment. On average, 79% of total N ingested was actually incorporated by the copepod whereas mean N losses as ammonium, eggs + fecal pellets represented only 12 and 9%, respectively. After a 24-h feeding period only 2% of N ingested was lost as DON. Inspection of individual DON pathways showed that both A. discaudata and C. helgolandicus highly contributed to total DON production via direct excretion (79 and 64%, respectively). The remaining DON appearing in the DON pool was derived from phytoplankton via direct release and/or indirect release (copepod ‘sloppy feeding’). |
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Keywords: | Copepods Nitrogen cycling N gross incorporation N net incorporation 15N tracer |
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