1Aix-Marseille Université, Université de Toulon, CNRS/INSU, IRD, MIO, UM 110, 13288, Marseille, CEDEX 09, France
2Université de Brest; Institut Universitaire Européen de la Mer, IUEM; Laboratoire des Sciences de l'Environnement Marin, UMR 6539 LEMAR, Technopôle Brest Iroise, Copernic, 29280 Plouzané, France
3Sorbonne Universités, UPMC Univ Paris 06, UMR 7621, Laboratoire d'Océanographie Microbienne, 66650 Banyuls/mer, France
4CNRS, UMR 7621, Laboratoire d'Océanographie Microbienne, 66650 Banyuls/mer, France
5Laboratoire de Biotechnologie de l'Environnement-INRA, UR0050, avenue des étangs 11100 Narbonne, France
6MODEMIC research team, UMR MISTEA, SUPAGRO, 2 place Viala 34060 Montpellier CEDEX 2, France
7Laboratoire d'Océanographie de Villefranche/Mer (LOV), CNRS-INSU, UMR7093, Observatoire Océanologique, 06230 Villefranche-sur-Mer, France
8Université Pierre et Marie Curie-Paris 6, UMR 7093, LOV, Observatoire Océanologique, 06230 Villefranche-sur-Mer, France
*now at: CNRS, UMR7144, Station Biologique de Roscoff, Place Georges Teissier, 29680 Roscoff, France
**now at: Sorbonne Universités, UPMC Univ Paris 06, UMR7144, Station Biologique de Roscoff, Place Georges Teissier, 29680 Roscoff, France
***now at: Laboratoire d'Océanologie et Géoscience (LOG), UMR CNRS 8187, Université du Littoral Côte d'Opale (ULCO), 32 avenue Foch, 62930 Wimereux, France
1Aix-Marseille Université, Université de Toulon, CNRS/INSU, IRD, MIO, UM 110, 13288, Marseille, CEDEX 09, France
2Université de Brest; Institut Universitaire Européen de la Mer, IUEM; Laboratoire des Sciences de l'Environnement Marin, UMR 6539 LEMAR, Technopôle Brest Iroise, Copernic, 29280 Plouzané, France
3Sorbonne Universités, UPMC Univ Paris 06, UMR 7621, Laboratoire d'Océanographie Microbienne, 66650 Banyuls/mer, France
4CNRS, UMR 7621, Laboratoire d'Océanographie Microbienne, 66650 Banyuls/mer, France
5Laboratoire de Biotechnologie de l'Environnement-INRA, UR0050, avenue des étangs 11100 Narbonne, France
6MODEMIC research team, UMR MISTEA, SUPAGRO, 2 place Viala 34060 Montpellier CEDEX 2, France
7Laboratoire d'Océanographie de Villefranche/Mer (LOV), CNRS-INSU, UMR7093, Observatoire Océanologique, 06230 Villefranche-sur-Mer, France
8Université Pierre et Marie Curie-Paris 6, UMR 7093, LOV, Observatoire Océanologique, 06230 Villefranche-sur-Mer, France
*now at: CNRS, UMR7144, Station Biologique de Roscoff, Place Georges Teissier, 29680 Roscoff, France
**now at: Sorbonne Universités, UPMC Univ Paris 06, UMR7144, Station Biologique de Roscoff, Place Georges Teissier, 29680 Roscoff, France
***now at: Laboratoire d'Océanologie et Géoscience (LOG), UMR CNRS 8187, Université du Littoral Côte d'Opale (ULCO), 32 avenue Foch, 62930 Wimereux, France
Received: 16 Dec 2013 – Discussion started: 07 Jan 2014 – Revised: 16 Jun 2014 – Accepted: 24 Jul 2014 – Published: 14 Oct 2014
Abstract. The significant impact of dust deposition on heterotrophic bacterial dynamics in the surface oligotrophic ocean has recently been evidenced. Considering the central role of bacteria in the microbial loop, it is likely that dust deposition also affects the structure and the functioning of the whole microbial food web. In the frame of the DUNE project, aiming to estimate the impact of dust deposition on the oligotrophic Mediterranean Sea through mesocosm experiments, the main goal of the present paper was to assess how two successive dust deposition events affect the dynamics of the microbial food web. The first dust seeding delivered new P and N to the amended mesocosms and resulted in a pronounced stimulation of bacterial respiration. It also induced pronounced, but transient, changes in the bacterial community composition. No significant effects were observed on the abundances of viruses and heterotrophic nanoflagellates. The second dust seeding also delivered new P and N to the amended mesocosms, but the effect on the microbial food web was very different. Bacterial respiration remained constant and bacterial abundance decreased. Compositional changes following the second seeding were minor compared to the first one. The decrease in bacterial abundance coincided with an increase in virus abundance, resulting in higher virus:bacteria ratios throughout the second seeding period. Our study shows that dust deposition to the surface oligotrophic ocean may involve important modifications of the trophic links among the components of the microbial food web with presumed consequences on C and nutrient cycling.
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