Heterogeneity in bacterioplankton abundance from 4.5 millimetre resolution sampling

A suite of pneumatically operated sampling devices was employed to investigate distributional patterns of marine bacteria at the millimetre scale. Spatial heterogeneity in bacterial abundance, or patchiness, was expressed as a coefficient of variation, and ranged from 5.5 to 75 %. Discrete regions of enhanced bacterial abundance, as well as clear gradients in abundance across entire sample arrays were observed, with changes in bacterial abundance of up to 16-fold observed across a distance of 32 mm. The role of turbulence in influencing bacterial distribution patterns was examined in a series of laboratory experiments. Levels of heterogeneity were found to be up to 6.5 times higher in stirred than unstirred water samples under laboratory conditions. The gradients in bacterial abundance observed here suggest that small-scale processes operate within the marine microenvironment to create and maintain spatial structure in the bacterioplankton community. We suggest that previously hypothesised nanoscale 'hot spots' and microzones exist only as maxima within a continuously variable distribution of bacteria within the marine environment.