Distribution and Activity of Attached and Free-Living Suspended Bacteria in the Bay of Fundy

We investigated the distribution of suspended bacteria in the Bay of Fundy on cruises in the spring, summer, and fall of 1979; a total of 22 stations were sampled throughout the Bay at the surface, midwater, and bottom. Free-living bacteria dominated the lower Bay in all seasons (0.2–4.0 × 10 6 cells∙mL −1 compared to 0.0–0.5 × 10 6 attached cells∙mL −1 ). Attached bacteria were more important in the upper reaches of the Bay with numbers as high as 2 × 10 6 cells∙mL −1 accounting for up to 94% of the total bacteria. Both the abundance and proportion of attached bacteria were strongly correlated with the concentration of suspended particulate matter. Average cell volume was not significantly different between spring (0.11 μm 3 , surface water only) and summer (0.09 μm 3 , all depths) and was similar for free-living and attached cells.Bacterial activity in summer and fall, based on uptake of [ 3 H]glutamic acid, generally followed the same pattern as cell numbers. Mean turnover time for glutamic acid in surface water was 64 h in summer and 205 h in fall. On a per cell basis, free-living bacteria in surface water were about twice as active as attached cells during summer, but only half as active during fall. The proportion of total activity due to attached cells increased with increasing substrate concentration.