8 



Decomposers, Bacteria, and 

 Microbenthos 



J. E. Hobble. T. Traaen, P. Rublee. J. P. Reed. M. C. Miller, and 

 T. Fenchel 



BACTERIA* 



Cell Numbers and Biomass 



Direct counts of bacteria in the ponds were made during the ice-free 

 periods in 1971 to 1973 using a modification of the method described by 

 Francisco et al. (1973). Briefly, this involved adding a solution of acridine 

 orange to a water sample, incubating for about 1 minute, and filtering 1 or 

 2 ml of the mixture through a black membrane filter. The filter was 

 immediately examined under epi-illumination with blue light and 

 fluorescent bacteria on the surface of the filter were counted. A more 

 detailed description of this method may be found in Daley and Hobbie 

 (1975) and an improved version in Hobbie et al. (1977). Sediment samples 

 were diluted at least 100:1 before mixing with a high-speed Waring 

 Blendor. Several milliliters were then treated as above. 



Direct counts from three ponds in 1971 (weekly samples), one pond in 

 1972 (eight samples), and two ponds in 1973 (two samples per week) (see 

 Hobbie and Rublee 1975) showed that total bacterial cell numbers in the 

 water column generally ranged from 0.1 to 6.0x10*' cells ml"'. In the 

 surface sediments the range was 0.1 to 55.0x10^ cells (g dry wt)~' of 

 sediment; cell numbers decreased with sediment depth (Table 8-1). When 

 the sediments and water column are compared, a square meter of the 

 sediments (5 cm depth) had a population of bacteria 3 to 4 orders of 

 magnitude greater than the water column (20-cm depth). Direct counts 

 made in 1973 (Figure 8-1) are representative of both the numbers and the 

 seasonal pattern of bacteria in these ponds. In the plankton, almost all of 

 the bacteria are free-living; that is, they were not attached to particles. In 

 contrast, most of the sediment bacteria are attached. 



Unfortunately, we did not find out until 1973 that when the 

 planktonic system was examined in detail, there was a great deal of 



*P. Rublee and J. E. Hobbie 

 340 



