AME 50:123-133 (2008)  -  DOI:

Dynamics of bacterial carbon metabolism at the entrance of a tropical eutrophic bay influenced by tidal oscillation

Mariana Guenther1,4,*, Rodolfo Paranhos1, Carlos Eduardo Rezende2, Eliane Gonzalez-Rodriguez3, Jean Louis Valentin1

1Departamento de Biologia Marinha, Instituto de Biologia, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ-CEP 21949-900, Brazil
2Laboratório de Ciências Ambientais, Centro de Biociências e Biotecnologia, Universidade Estadual do Norte Fluminense, Campos dos Goytacazes, RJ-CEP 28013-602, Brazil
3Departamento de Oceanografia, Instituto de Estudos do Mar Almirante Paulo Moreira, Comando da Marinha, Arraial do Cabo, RJ-CEP 28930-000, Brazil
4Present address: Departamento de Oceanografia, Universidade Federal de Pernambuco, Recife, PE-CEP: 50670-901, Brazil

ABSTRACT: Bacterial metabolic rates were assessed at the entrance to Guanabara Bay, SE Brazil, during the summer (i.e. wet) season, in order to evaluate short-term effects of tidal oscillation on the magnitude of carbon flow through the bacterioplankton. Bacterial production (BP), respiration (BR) and abundance, phytoplankton production and biomass, particulate and dissolved organic matter (POM and DOM) concentrations and elemental composition, nutrient concentrations and hydrological profiles were estimated at a fixed station during 3 consecutive days with intervals of 3 h, in surface and bottom (20 m) layers. The study period covered the end of the spring tide and the beginning of the neap tide. Bacterial metabolic rates were highly variable, and a small fraction of the dissolved organic carbon (DOC) pool was used by bacterioplankton (DOC turnover: 23 to 71 d). The input of allochthonous DOC, inferred from DOM elemental composition (C:N:Psurface ~150:9:1; C:N:Pbottom ~245:6:1), and temperature were the main controlling factors of bacterial carbon metabolism. Although the magnitude of carbon flow through the bacterioplankton was highly variable, there were nevertheless consistent differences between layers. At the surface, the particulate organic carbon (POC) production (~14.3 µM C h–1), mainly due to phytoplankton, was higher than BR, and bacterioplankton acted equally as POC producers and DOM remineralizers (bacterial growth efficiency ~52%). Near the bottom, BR was equivalent to total POC production (~0.3 µM C h–1) and higher than BP (~0.05 µM C h–1), and thus bacteria acted mostly as a DOM sink. This study highlights the importance of short-term variations in carbon flow through bacteria for understanding the carbon cycle of estuarine systems.

KEY WORDS: Bacterial production · Bacterial respiration · Bacterial growth efficiency · Carbon flux · Guanabara Bay · Estuary

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Cite this article as: Guenther M, Paranhos R, Rezende CE, Gonzalez-Rodriguez E, Valentin JL (2008) Dynamics of bacterial carbon metabolism at the entrance of a tropical eutrophic bay influenced by tidal oscillation. Aquat Microb Ecol 50:123-133.

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