MEPS 228:15-24 (2002)  -  doi:10.3354/meps228015

Control of bacterial production in cold waters. A theoretical analysis of mechanisms relating bacterial production and zooplankton biomass in Disko Bay, Western Greenland

T. Frede Thingstad1,*, Torkel Gissel Nielsen2, Anja Skjoldborg Hansen2, Henrik Levinsen2,**

1Department of Microbiology, University of Bergen, Jahnebakken 5, 5020 Bergen, Norway
2Department of Marine Ecology, National Environmental Research Institute, PO Box 358, 4000 Roskilde, Denmark
*E-mail: **Present address: University of Copenhagen, Helsingørsgad 49-51, 3400 Hillerød, Denmark

ABSTRACT: Data on planktonic bacterial production and biomass of copepods and heterotrophic dinoflagellates in Disko Bay, Greenland, are discussed within the framework of a theoretical model. The model is an extension of a previously published model that relates bacterial production and shifts between carbon and mineral nutrient limitation of bacteria to the structure of the planktonic food web. We suggest how dinoflagellates can be incorporated into this framework, and show how this affects bacterial production. With the parameters used, the model predicts the system mainly to be in, or close to, the state leading to carbon-limited bacterial growth, a prediction in accordance with results published for this environment. In the model, this is caused by a high combined biomass of copepods and heterotrophic dinoflagellates that keeps the biomass of phytoplankton competitors low and the regeneration rate high. In Disko Bay, high copepod biomass is not primarily the result of a succession from a high phytoplankton biomass to their predators, but is largely caused by migration of an over-wintering copepod population from deep waters into the photic zone prior to the spring bloom. The set of data thus comprises no situations combining high phytoplankton biomass with low combined biomass of heterotrophic dinoflagellates and copepods, a situation that in the model would lead to a state with pronounced mineral nutrient limitation of bacterial growth rate. Since such seasonal copepod migration is a feature common to many arctic ecosystems, the suggested relationship has strong potential implications for carbon cycling in the Arctic.

KEY WORDS: Bacterial growth · Polar · Food web models · Copepods

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