Viral and bacterial dynamics in Arctic sea ice during the spring algal bloom near Resolute, N.W.T., Canada

Abstract

High virus counts were found in Arctic sea ice samples taken during the spring ice algal bloom near Resolute, Northwest Territories, Canada. Viral abundances in the sea ice ranged from 3.7 X 10" viruses m-2 (or 9.0 X 106 ml-l) to 4.9 X 10" m-2 (1.3 X 10' ml-l) which is 10-to 100-fold greater than the concentration of viruses in the underlying water column (1.1 X 106 ml-l). This increase in viral abundance corresponds with the 10-to 100-fold increase in bactenal abundance in sea ice as compared with the water column. Bacterial abundances ranged from 6.1 X 10' bacteria n1r2 (1.5 X 105 ml-l) to 4.2 X 10'' m-2 (1.0 X 107 ml-l) from early to late spring respectively. The virus-to-bacteria ratios (VBR) were among the highest reported in natural samples. The greatest viral abundances occurred in the 0.5 to 1.5 cm layer of the ice profile, where the bacteria were most active. The VBR generally decreased during the spring although viruses were increasing in abundance. The disequilibrium between phage and bacterial growth and abundance maxima during the spring bloom is suggested to be due to (1) a change in the makeup of the bacterial community, such that phage-resistant bacteria proliferated later in the spring, or (2) an increase in viral lytic activity with higher bacterial cell-specific growth rates; both viral lytic activity and bacterial growth rates declined later in the spring as the bacterial populatlon reached its peak.