Microscale patchiness of bacterioplankton assemblage richness in seawater

Abstract

We sought to test the hypothesis that bacterial species richness and composition vary at the millimeter scale in the marine pelagic environment, in response to the heterogeneous distribution of organic matter. To test this hypothesis, it was necessary to design and test a protocol to sample, lyse and analyze (by polymerase chain reaction/denaturing gradient gel electrophoresis [PCR-DGGE]) bacterioplankton species richness in a single microliter of seawater. Significant variation in bacterial species richness was found amongst 1 μl samples. Greater species richness was seen when seawater was enriched with diatom detritus. Examination of species richness at 2 mm intervals over a 20 mm transect showed greater variability during the peak abundance of Lingulodinium polyedrum when compared to the late stage of the bloom. Overall species richness was highest in samples enriched with organic particles. These results suggest that particulate organic matter may, in part, regulate the level of bacterial species richness as well as cause patchiness in the small-scale distribution of species. Microscale patchiness of bacterial species may have important implications in carbon cycling and biogeochemistry, not only at the microscale but also at the ocean basin scale.