Degradation of phytoplankton detritus by bacteria, estimation of bacterial consumption and respiration in an oxygen chamber

Consumption of the dissolved compounds of phytoplankton detritus (dinoflagellates, diatoms) by natural bacterial populations of the Kiel Bight area was studied. Experiments simulated the situation during degradation of a phytoplankton bloom in the water column, when high concentrations of dissolved organic material are released. The experiments were conducted in a chamber which allowed continuous monitoring of the oxygen concentratlon. Subsamples were taken at short time intervals for determination of bacterial number and biomass, and of dissolved organic compounds (concentration and molecular weight). These experiments allowed evaluation of the bacterial biomass increase in the absence of predators, without addihon of a labelled substrate. The bacteria consumed dissolved substances very rapidly, resulting in an increase of bacterial biomass of more than 500 fig Cl-Id-'. It was shown by oxygen measurements, that up to 80 % of the bacterial gross uptake was respired. This indicates the importance of bacteria as remineralizing organisms in the water column.