Changes in the genetic and metabolic diversity of the bacterioplankton in Disko Bay, western Greenland, were followed during the post-spring phytoplankton bloom. Samples were taken at different depths every 2 to 3 d from 1 to 23 June 2001. The highest bacterial abundance was found at the depth of the fluorescence maximum (FM). Average cell numbers at FM were around 6 x 105 cells ml-1, but numbers were highly variable. Immediately following a rapid decline in the phytoplankton biomass from 31 to 8 mg chl a m-3, a peak in numbers of culturable bacteria was observed reaching 3 x 104 CFU ml-1. Concomitant with the changes in phytoplankton biomass and bacterial culturability, the genetic diversity of the bacterioplankton communities changed as assessed by DGGE. At FM, DGGE fingerprints shifted between 6 and 8 June; however, they returned to the initial profile between 10 and 14 June. Similarly, successional shifts in the diversity of the culturable bacteria were observed as the populations before and after the peak in CFUs were significantly different. Accompanying the changes in genetic diversity, the metabolic diversity of the bacterial communities shifted and the communities became adapted to growth on refractory carbon sources such as cellulose and xylan. Our investigation thus demonstrates intimate links between phytoplankton and bacterioplankton and that the spring phytoplankton bloom strongly affects the genetic diversity and functional characteristics of the heterotrophic bacterial communities in Disko Bay.