We provide evidence, based on the assessment of bacterial abundance in a series of samples representing geometrically decreasing volumes (5 1 to 0.25 ml), for the existence and scale dependence of patchiness in mixed-layer marine bacterioplankton. Our results demonstrate the existence of strong bacterioplankton patchiness at centimetre scale, the bacterioplankton community appearing as homogeneous when sampling at larger or smaller scales. We also provide, based on the inferred frequency distribution of bacterial densities, a representation of the in situ spatial distribution of the bacterioplankton population sampled This distribution depicts the bacterioplankton community as composed of high density (> 107 bacteria ml-l) bacterial patches scattered within a 'matrix' of low bacterial density (105 bacteria ml-l). These results imply that the processes regulating bacterial abundance operate at centimetre scale

6 pages, 6 figures

Peer Reviewed