AME 63:183-191 (2011)  -  DOI: https://doi.org/10.3354/ame01495

ABSTRACT: Eleven culture experiments were conducted in the coastal upwelling ­system of the Ría de Vigo (NW Iberian Peninsula) by inoculating GF/C filtrated (10%) in 0.2 µm filtrated (90%) surface seawater collected under contrasting hydrographic conditions. Short-term (4 d) laboratory incubations were performed in the dark at 15°C. Dissolved organic carbon (DOC) concentration, bacterial biomass (BB), bacterial production (BP) and electron transport system (ETS) activity were then monitored to: (1) study the course of bacterial carbon demand (BCD) and growth efficiency (BGE) during the incubation period; and (2) determine how BCD and BGE were linked with changing environmental conditions. Following the 4 d incubation, BP decreased by <4 times its initial values (range from 3 to 11 times) and ETS activity increased by 6 times its initial values (range from 1 to 75 times). As a result, BCD increased by 5 times (range from 1 to 16 times) and the BGE decreased by 15 times (range from 2 to 55 times) over the same period. BGE integrated over the 4 d incubation period ranged from 7 ± 1% to 55 ± 11% (mean ± SD: 27 ± 15%); integrated BGE increased significantly (R² = 0.64, p < 0.003) with the initial concentration of dissolved inorganic nitrogen (DIN), and decreased significantly (R² = 0.55, p < 0.01) with the C:N ratio of the bioavailable dissolved organic matter (BDOM). A multiple linear regression with DIN and the C:N ratio of BDOM explained 89% of the observed variability in the integrated BGE, demonstrating the strong dependence of growth efficiency on nutrient conditions and the quality of the organic substrate feeding the community of this coastal embayment.

KEY WORDS: Bacterial carbon demand · Bacterial growth efficiency · Inorganic nutrients · DOM ­stoichiometry · Coastal upwelling