220 



V. Alexander et al. 



12 3 4 



12 3 4 Subponds 



After 5 days After 15 days 

 *Note chonge in scale 



FIGURE 5-27. Phytoplankton biomass 

 (expressed as volume) in subponds, initi- 

 ally (Day 0), and after 5 and 15 days. 

 Treatments are as described for Figure 

 5-26. 



Rates of ciliate feeding on algae have been measured, but for the 

 chironomids and micrometazoans only an estimate can be made (Fenchel 

 1975). The ciliates and micrometazoans consume a total of no more than 8 

 mg algal C m"^ day \ Based on the measured value (325 mg C m"^ 

 day"^) of total ingestion by the chironomids and the organic composition 

 of the sediment given above, the chironomid population in the ponds 

 would consume only about 0.2 mg algal C m"^ day"' if their ingestion is 

 non-selective. If, as Kajak and Warda (1968) imply, chironomid larvae 

 have a selectivity of 5:1 for epipelic algae over detritus, the algal 

 consumption by the tundra pond population of chironomids would be 

 approximately 1 mg algal C m ~ ^ day " ' . 



A large percentage of the total algae consumed by benthic grazers is 

 "buried" epipelic algae, and therefore does not directly affect the 

 productivity of the epipelic algae. Perhaps only about 1 mg of the total 

 daily consumption of 9 mg algal C m"^ by micrometazoans and 

 chironomids is "surface" epipelic algae since this component is limited to 



