Phytoplankton-Heterotrophic Coupling: Measurements of Respiratory Activity in Samples of Fractionated Seawater
Pipas, J. Marc
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There has in recent years been mounting evidence to suggest that bacterial activity may represent a large portion of the total metabolic activity of the marine ecosystem. In this project, samples of filtered seawater were measured for changes in dissolved oxygen levels over a 48 hour period to attempt to assess the relative importance of the different size fractions of organisms in total metabolic activity. It was shown that water samples filtered through lum screening had metabolic activity greater than unfiltered samples. Through measurements of levels of dissolved nutrients before and after the filtration process, it was shown that the increased metabolic activity was not due to any changes in nutrient levels caused by filtering the seawater. Rather, it is suggested that this increased activity in the filtered fractions was due to removal of grazing pressure by the microflagellates on the bacterial component. In addition through injection of glucose into some samples it was shown that substrate limitation of metabolic activity occurs in the natural system.