BG Biogeosciences BG Biogeosciences 1726-4189 Copernicus Publications Göttingen, Germany 10.5194/bg-5-1573-2008 Seasonal to hour variation scales in abundance and production of total and particle-attached bacteria in the open NW Mediterranean Sea (0–1000 m) Mével G. 1 2 3 Vernet M. 1 2 3 Goutx M. 4 Ghiglione J. F. 5 6 CNRS, UMR 7144, Equipe de Chimie Marine, Station Biologique de Roscoff, 29682 Roscoff, France UPMC, Univ Paris 06, UMR 7144, Station Biologique de Roscoff, 29682 Roscoff, France UBO, Institut Universitaire Européen de la Mer, 29280 Plouzané, France Laboratoire de Microbiologie, Géochimie et Ecologie Marines; Université de la Méditerranée; Centre d'Océanologie de Marseille, CNRS (UMR 6117), Campus de Luminy, case 901, 13288 Marseille Cedex 09, France CNRS, UMR 7621, Laboratoire d'Océanographie Biologique de Banyuls, Avenue Fontaulé, BP44, 66650 Banyuls sur mer, France UPMC, Univ Paris 06, UMR 7621, Laboratoire ARAGO, Avenue Fontaulé, BP 44, 66650 Banyuls sur mer, France 20 11 2008 5 6 1573 1586 Copyright: © 2008 G. Mével et al. 2008 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://bg.copernicus.org/articles/5/1573/2008/bg-5-1573-2008.html The full text article is available as a PDF file from https://bg.copernicus.org/articles/5/1573/2008/bg-5-1573-2008.pdf

We present the vertical and temporal dynamics of total <i>vs.</i> particle-attached bacterial abundance and activity over a 5 week period under summer to autumn transition in NW Mediterranean Sea. At a weekly time scale, total bacterial biomass and production in the euphotic layers was significantly correlated with phytoplanktonic biomass. At an hourly time scale, total bacterial biomass responded very rapidly to chlorophyll <i>a</i> fluctuations, suggesting a tight coupling between phytoplankton and bacteria for resource partitioning during the summer-autumn transition. In contrast, no influence of diel changes on bacterial parameters was detected. Episodic events such as coastal water intrusions had a significant positive effect on total bacterial abundance and production, whereas we could not detect any influence of short wind events whatever the magnitude. Finally, we show that particle-attached bacteria can represent a large proportion (up to 49%) of the total bacterial activity in the euphotic layer but display rapid and sporadic changes at hourly time scales. In the mesopelagic layers, bacterial abundance and production linearly decreased with depth, except some production peaks at 400–750 m. This study underlines the value of large datasets covering different temporal scales to clarify the biogeochemical role of bacteria in the cycling of organic matter in open seawater.

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