Bacterial dynamics in first year sea ice and underlying seawater of Saroma-ko Lagoon (Sea of Okhotsk, Japan) and resolute passage (High Canadian Arctic): inhibitory effects of ice algae on bacterial dynamics.

The seasonal development of bacterial abundance in first year bottom ice and underlying seawater were studied at Saroma-ko Lagoon in Hokkaido, Japan, and at Resolute Passage in the High Canadian Arctic during the algal bloom in spring 1992. The aim of this study was to evaluate whether the high algal concentrations reached during the bloom of ice algae have inhibitory effects on bacterial dynamics. Bacterial abundance (measured as total cell count and colony-forming units CFU) increased with the increase of the algal biomass up to 500 micrograms Chla.L-1 in both locations. Culturable fraction (measured as the percentage of CFU counts versus the total cell counts) was between 7% and 22% at Saroma-ko, and approximately 0.08% at Resolute Passage. When algal biomass exceeded 500 micrograms of Chla.L-1, both bacterial abundance and culturable fraction decreased significantly. There was a maximum threshold of algal biomass (between 500 and 800 micrograms of Chla.L-1) after which bacterial dynamics become negatively coupled to the algal biomass. These results suggest that bactericidal and/or bacteriostatic compounds from these extremely high algal concentrations could explain the decrease in bacterial abundance and culturability in bottom ice observed after the ice algae bloom.