Primary Producers 219 



controls; at a lower dose rate (1975), there was an increase in algal 

 biomass after a lag period. 



Experiments in small subponds (240 liters) in 1976 tested the effect of 

 removal of zooplankton with and without added oil (Figures 5-26, 5-27). 

 The same effect was observed: after a lag of 2 weeks, oiled subponds 

 recovered and had about the same primary productivity and algal biomass 

 as did the controls. However, the pond containing no zooplankton had a 5- 

 fold increase in primary production after 16 days and algal biomass also 

 increased. Our conclusion is that zooplankton indeed are controlling algal 

 biomass in the plankton of these ponds. 



A similar question could be asked about control of sediment algae. 

 However, epipelic algae make up only a small fraction of the total 

 potential diet of benthic grazers. The sediment organic carbon is about 

 0.06% algae, 0.17% bacteria, and 99.77% detritus. The biomass of the 

 epipelic algae ranges from 0.5 to 1.0 g C m ' while the biomass of the 

 sediment bacteria is approximately 3 g C m~^ but these organisms are 

 very much diluted by the large amount of detrital carbon (1700 g C m^^) 

 in the top 5 cm of pond sediments. Consequently, unless the benthic 

 grazers (primarily chironomids, oligochaetes, and micrometazoans) are 

 highly selective feeders, they probably could not have a very significant 

 effect on the epipelic algae. 



5.0 



4.0 



■^3.0 



o 



o 



20 



FIGURE 5-26. Primary produc- 

 tion (the ratio of experiment to 

 control) in subponds after vari- 

 ous treatments. (After Federle et 

 al. 1979.) 



