MICROSCALE DISTRIBUTION OF BACTERIOPLANKTON IN RELATION TO PHYTOPLANKTON - RESULTS FROM 100-NL SAMPLES

The microspatial distribution of marine bacterioplankton was investiga ted by comparing the bacterial abundance in 100-nl subsamples of natur al seawater. For sampling, staining with DAPI, and filtering, we desig ned capillary microtips that allowed pipetting of 100 nl with a sampli ng error <10%. Highly significant correlations were obtained between t he 100-nl method and the conventional direct-counting method. Frequenc y distributions of bacterial cells were determined in experiments with natural seawater during bloom conditions as well as with seawater enr iched with diatom cells from cultures of Chaetoceros muelleri. Bacteri a in 100-nl subsamples were normally distributed in each single experi ment and in the Formalin-fixed control. Mean bacterial abundance in su bsamples containing at least one phytoplankton cell was never signific antly different from samples lacking algal cells. Based on our results we conclude that bacteria are homogeneously distributed in subsample volumes of 100 nl, and therefore we could not verify the current conce pt that bacteria may cluster around phytoplankton cells.