On the role of heterotrophic bacteria in marine ecosystems: Some problems

Abstract

Resulting from synecological studies in some areas of the southern North Sea, a contradiction becomes evident between measurements of primary production and determinations of the activities consuming organic matter. In the Southern Bight, the consumption in 10 times higher than the production. This means that the primary production has been underestimated, and/or the consumption over-estimated. In order to discuss the validity of the methods used for determining the respiration activities, some results are presented: (a) during a 24-h cycle at the Sluice-Dock of Ostend, the variations of the oxygen concentration in the water are explained by the measured activities and diffusion fluxes; (b) two different methods are shown to give comparable results: the initial rate of oxygen consumption and the anaplerotic fixation of CO2. The other possible sources of error lie mainly in the extrapolations ones has to make in order to establish a general budget: (a) extrapolation in time is very difficult because of important variations of organic matter and respiration activities to be observed during a 24-h cycle; (b) extrapolation in function of the depth does not seem very difficult in the case of shallow, entirely mixed water masses. No argument was found against the validity of the methods used for the determination of respiration activities. Therefore, the question remains open as to which parameters are over-estimated or under-estimated by actual methods.