MEPS 239:263-276 (2002)  -  doi:10.3354/meps239263

Bacterioplankton dynamics in the Gulf of Aqaba and the northern Red Sea in early spring

Hans-Peter Grossart*, Meinhard Simon

Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, 26111 Oldenburg, Germany

ABSTRACT: The northern Red Sea, with its northernmost extension the Gulf of Aqaba, is an oligotrophic marine ecosystem, for which the growth and substrate dynamics of the heterotrophic bacterioplankton have not yet been studied. In 1999, we carried out a comprehensive investigation of bacterioplankton growth dynamics in early spring (February/March), a time of year when the Gulf waters are deeply mixed, while permanent stratification prevails in the northern Red Sea. Most of the parameters measured yielded low values (bacterial numbers: 0.5 to 12.8 x 105 ml-1; production: 0.9 to 56.8 ngC l-1 h-1; growth rates: <0.01 to 0.15 d-1; turnover rates of dissolved free amino acids, DFAA: 0.008 to 1.35 d-1; glucose: 0.001 to 0.14 d-1; and concentrations of dissolved free neutral monosaccharides: <2 to 86 nM). Glucose was the only monosaccharide detected in 93% of the samples. Concentrations of DFAA ranged from 13.2 to 176 nM, and those of dissolved combined amino acids and neutral monosaccharides from 0.42 to 3.69 µM and 0.05 to 3.31 µM, respectively. Uptake of glucose (as percent of bacterial production) in 93% of the samples was <50%, whereas that of DFAA was much higher, often exceeding 100% (the latter result may have been due to methodological biases). Most of the parameters measured were more variable and covered a wider range in the northern Red Sea than in the Gulf, where vertical patterns were more homogenous. Only concentrations of dissolved free neutral monosaccharides were systematically lower in the northern Red Sea. Bacterial production in this area was significantly correlated with turnover and uptake rates of DFAA, and with glucose turnover rates below 100 m. Aminopeptidase and β-glucosidase activities were fairly similar in both study areas, with means ranging from 19.4 to 29.9 nmol l-1 h-1. Whereas aminopeptidase hydrolysis rates were in the same range as values found in other oceanic regions, β-glucosidase hydrolysis rates were much higher, possibly due to the persistence of active β-glucosidase in the dissolved phase, as has been reported for alkaline phosphatase in this area. Analysis of the data indicates that in the northern Red Sea bacterioplankton growth dynamics were mainly controlled by biological processes, whereas in the Gulf hydrographic processes were more important.

KEY WORDS: Bacteria · Bacterial production · Amino acids · Carbohydrates · Turnover rates · Aminopeptidase · Glucosidase · Gulf of Aqaba · Red Sea

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