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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 15, issue 20 | Copyright

Special issue: Interactions between planktonic organisms and biogeochemical...

Biogeosciences, 15, 6019-6032, 2018
https://doi.org/10.5194/bg-15-6019-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 15 Oct 2018

Research article | 15 Oct 2018

Nitrogen and phosphorus recycling mediated by copepods and response of bacterioplankton community from three contrasting areas in the western tropical South Pacific (20° S)

Valentina Valdés1,2, François Carlotti3, Ruben Escribano4,5, Katty Donoso3, Marc Pagano3, Verónica Molina6, and Camila Fernandez2,7,8 Valentina Valdés et al.
  • 1Programa de Doctorado en Oceanografía, Departamento de Oceanografía, Facultad de Ciencias Naturales y Oceanográficas, Universidad de Concepción, Concepción, Chile
  • 2Sorbonne Université, UPMC Univ Paris 06, Laboratoire d'Océanographie Microbienne (LOMIC), Observatoire Océanologique de Banyuls/Mer, 66650, Banyuls/Mer, France
  • 3Aix-Marseille Univ, Universite de Toulon, CNRS, IRD, OSU PYTHEAS, Mediterranean Institute of Oceanography MIO, UM 110, 13288, Marseille, Cedex 09, France
  • 4Departamento de Oceanografía, Universidad de Concepción, Concepción, Chile
  • 5Instituto Milenio de Oceanografía, Universidad de Concepción, Concepción, Chile
  • 6Departamento de Biología and Programa de Biodiversidad, Facultad de Ciencias Naturales y Exactas, Universidad de Playa Ancha, Playa Ancha, Valparaíso, Chile
  • 7FONDAP INCAR center (15110027), and PFB-31 COPAS Sur Austral Program, Departamento de Oceanografía, Universidad de Concepción, Concepción, Chile
  • 8Centro FONDAP de Investigación en Dinámica de Ecosistemas Marinos de Altas Latitudes (IDEAL), Valdivia, Chile

Abstract. Zooplankton play a key role in the regeneration of nitrogen and phosphorus in the ocean through grazing and metabolism. This study investigates the role of the organic and inorganic nitrogen and phosphorus compounds released by copepods on biogeochemical processes and on the microbial community composition during the OUTPACE cruise (18 February–3 April 2015) at three long-duration stations (LD). Two LD stations were located in the Melanesian Archipelago region (MA; LD A and LD B) and one in the South Pacific Gyre (SG; LD C), which represent oligotrophic and ultra-oligotrophic regions respectively. At each station, on-board microcosm experiments were performed with locally sampled organisms, comprising a mix of epipelagic copepods fed with their natural food and then incubated along with wild microbial assemblages. In the presence of copepods, ammonium and dissolved organic nitrogen showed a significant increase compared to a control in two situations: in ammonium concentration (rate: 0.29µmolL−1h−1 after 4h of incubation) in LD C and in dissolved organic nitrogen concentration (rate: 2.13µmolL−1h−1 after 0.5h of incubation) in LD A. In addition, during the three experiments, an enhanced remineralization (ammonification and nitrification) was observed when adding copepods compared to the controls. A shift in the composition of the active bacterial community was observed for the experiments in LD A and LD B, which were mainly characterized by an increase in Alteromonadales and SAR11, respectively, and linked with changes in nutrient concentrations. In the experiment performed in LD C, both groups increased but at different periods of incubation. Alteromonadales increased between 1 and 2h after the beginning of the experiment, and SAR 11 at the end of incubation. Our results in near in situ conditions show that copepods can be a source of organic and inorganic compounds for bacterial communities, which respond to excretion pulses at different timescales, depending on the initial environmental conditions and on their community composition. These processes can significantly contribute to nutrient recycling and regenerated production in the photic zone of ultra-oligotrophic and oligotrophic oceanic regions.

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The role of N and P released by copepods on biogeochemical cycles and the microbial community during the OUTPACE cruise was studied. In the presence of copepods, NH4+ and DON increase, and an enhanced remineralization was observed. A shift in active bacterial composition was observed, linked with changes in nutrient concentrations. Copepods can be a source of (in)organic compounds for bacterial communities that contribute to nutrient recycling and regenerated production in the photic zone.
The role of N and P released by copepods on biogeochemical cycles and the microbial community...
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