Distribution of picophytoplankton and bacterioplankton along a river plume gradient in the Mediterranean Sea
Joux, F.; Servais, P.; Naudin, J.J.; Lebaron, P.; Oriol, L.; Courties, C. (2005). Distribution of picophytoplankton and bacterioplankton along a river plume gradient in the Mediterranean Sea. Vie Milieu (1980) 55(3-4): 197-208
In: Vie et Milieu. Observatoire Oceanographique Banyuls: Banyuls-sur-Mer. ISSN 0240-8759, meer
The Rhone River (France) is an important river that flows into relatively nutrient-poor Mediterranean waters resulting in the formation of chemical and physical gradients. The distribution of picophytoplankton and bacterioplankton was studied along the salinity gradient in the Rhone River plume in November 1998, March 1999 and April 1999. Abundances of three groups of picophytoplankton (Prochlorococcus [PRO], Synechoccocus [SYN], small eukaryotic cells [PEUK]) and two clusters of bacteria differing by their nucleic acid content were determined by flow cytometry. PRO were abundant in November in the river plume (7-23 x 103 cells.ml-1) but were not observed in March and April. Abundances of SYN (3-20 x 103 cells.ml-1) and PEUK (0.5-4 x 103 cells.ml-1) were similar in November and March. In April, the concentrations of chlorophyll a (Chl a) peaked (> 15 µg.L-1) at intermediate salinities (30 to 35). At this time, the distribution of PEUK followed the same pattern as Chl a concentrations, while SYN abundances were negatively correlated to Chl a concentrations. Bacterial abundance and production were both well correlated to Chl a concentration in April, whereas only bacterial production was correlated with Chl a concentrations in March. In April, the abundance of bacteria with a high nucleic acid content (HNA) was more closely correlated to bacterial production and Chl a concentrations than those of bacteria with a low nucleic acid content (LNA). This suggests that HNA bacteria have a higher contribution to bacterial production than LNA bacteria during this productive period.
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