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 an d 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 alga l concentrations reached during the bloom of ice algae have inhibitory effe cts on bacterial dynamics. Bacterial abundance (measured as total cell coun t and colony-forming units CFU) increased with the increase of the algal bi omass up to 500 mu g Chla.L-1 in both locations. Culturable fraction (measu red as the percentage of CFU counts versus the total cell counts) was betwe en 7% and 22% at Saroma-ko, and approximately 0.08% at Resolute Passage. Wh en algal biomass exceeded 500 mu g of Chla.L-1, both bacterial abundance an d culturable fraction decreased significantly. There was a maximum threshol d of algal biomass (between 500 and 800 mu g of Chla.L-1) after which bacte rial dynamics become negatively coupled to the algal biomass. These results suggest that bactericidal and/or bacteriostatic compounds from these extre mely high algal concentrations could explain the decrease in bacterial abun dance and culturability in bottom ice observed after the ice algae bloom.