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c 

 o 



w 

 O 



o 



c 







o 

 a> 



u 400 800 1200 1600 



Zooplankton Production 



FIGURE 6-18. The maximal biomass 

 of zooplankton and the total zooplank- 

 ton production plotted against the 

 mean sestonic organic carbon during 

 June, July and August for ponds in 

 1971 (circles), 1972 (squares) and 1973 

 (triangles). 



highly significant. Zooplankton biomass was the smallest in 1971, the year 

 the algae and bacteria made up only 4.6 to 5.3% of the total seston. In 

 contrast, the biomass was highest in 1972 when the seston was 13.4% algae 

 and bacteria. Pond E had been subjected to an oil spill in 1970 which killed 

 all the zooplankton. Biomass was very low in 1971 and consisted only of 

 Cyclops sp. and fairyshrimp. Although the differences are not significant. 

 Pond E did have a high seston concentration and a low ratio of living 

 matter to detritus. 



The relationship between the seston concentration and zooplankton 

 production (Figure 6-18) is not as good a fit to a straight line as was the 

 biomass to seston relationship, but the trend is obviously the same. Thus, 

 the high seston concentrations are present only when both zooplankton 

 biomass and production are low. At the same time, the absolute amount of 

 living biomass remains constant and the living material becomes a higher 

 percentage of the seston (Figure 6-17). One explanation is that grazing by 

 zooplankton will reduce both living and dead material but the living 

 material is replenished rapidly, so in a steady-state its percentage of the 

 total seston rises. From this, we might expect that reduction of the 

 zooplankton would result in higher seston concentrations and a lower 

 living to detritus ratio; this occurred in Pond E following the oil spill. If a 

 better quality food results from the increase in percentage of algae and 

 bacteria, then there would be a positive feedback with better quality food 

 leading to higher production leading to still better quality food, etc. 



