AME 37:23-32 (2004)  -  doi:10.3354/ame037023

Bacterioplankton abundance and growth in a river-dominated estuary: relationships with temperature and resources

George B. McManus1,*, Patrick M. Griffin2, Jonathan R. Pennock3

1Department of Marine Sciences, University of Connecticut, Groton, Connecticut 06340, USA
2Dauphin Island Sea Lab, University of South Alabama, Dauphin Island, Alabama 36528, USA
3Marine Program, University of New Hampshire, Durham, New Hampshire 03824, USA

ABSTRACT: We measured bacterial abundance and productivity, along with other biological, chemical, and physical variables, during a 17 mo study in Mobile Bay, USA. Mobile Bay is a shallow, river-dominated estuary, with highly variable freshwater inputs and relatively short freshwater residence time (ca. 2 to 3 wk). In addition to the field measurements, we performed bioassay experiments to evaluate the degree of resource limitation of the bacterioplankton. As in other seasonally variable estuaries, temperature appeared to be an important regulator of bacterioplankton in Mobile Bay, with minima in abundance and growth rates occurring during winter. The bioassay experiments, in which an inoculum of the natural bacterioplankton community was diluted into filtered bay water and incubated for 4 d, always resulted in rapid net growth, indicating the presence of labile substrates. The net yield of bacterial cells in these assays was always equal to or greater than the abundance of in situ populations, suggesting that an amount of substrate about equal to in situ biomass divided by growth efficiency was present year round. During winter, the yields in the bioassays were highest, suggesting an accumulation of resources when bacterial growth was limited by temperature.

KEY WORDS: Bacteria · Mobile Bay · Gulf of Mexico · Thymidine · Epifluorescence · Seawater culture

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