202 



V. Alexander et al. 



1.0 



0.8 



g'O.G 



0.4 



2 0.2 



Q. 



25 Jun 



Epipelic 



Planktonic 



L- L- 



8 14 20 



Temperature, °C 



8 14 20 



Temperature, °C 



1.0 



0.8 



0.6 



E 



Q. 



0.4 



2 0.2 



1.0 



- 12- 



- 6 



- 3 



0.8 - 



EO.6 - 



0.4 



2 0.2 - 



28 Aug 



- 12 



8 14 20 



Temperofure, °C 



I— i 



9'E 

 o 



E 



- 6 



E 

 Q. 



- 3 -s 



8 14 20 



Temperature, °C 



FIGURE 5-14. P^Qj(. of phytoplankton and epipelic algae at four temper- 

 atures in Ponds A and B, 1973. 



response of the two groups to temperatures below the phytoplankton 

 optimum probably are significant. Thus, the ^lo values between 2.5° and 

 12.5°C as calculated from the weekly Pmax estimates averaged 3.0 (range 

 2.4 to 3.4) for the plankton algae and 2.2 (range 1 .6 to 3.0) for the epipelic 

 algae. This latter value is similar to the ^lo found for a benthic algal mat 

 in two Antarctic ponds by Goldman et al. (1963) and is within the range of 

 2 to 4 considered typical for algae by Fogg (1965). The plankton values, on 

 the other hand, are much higher than the 1.5 reported by Kalff (1969) for 

 the plankton of two nearby Barrow ponds. His data were based on 

 measurements at 10° and 20°C and would be an underestimation if the 

 algae had a 15°C temperature optimum. In addition, Kalff employed a 

 long incubation period (up to 40 hours) during which an unexplained 

 decrease in photosynthesis rates took place. 



These contrasting responses of planktonic and epipelic photosynthesis 

 to temperature suggest adaptation of each group to its particular 



