260 R. G. Stross et al. 



TABLE 6-3 Least Squares Linear Regression Coefficients for Brood Size vs. 

 Length of Daphnia middendorffiana/rom Barrow, Alaska 



*Only two non-zero brood sizes were observed. 



and b. In comparison, the exponent, b, for D. pulex in the trough ponds 

 was roughly 5.0. Thus, despite the variability from year to year, the 

 increase in number of each brood for an increase of 1 mm body length was 

 lower in D. pulex than in D. middendorffiana. 



During the 3 years of study in Pond C, the biomass of fairyshrimps 

 decreased steadily while that of Daphnia middendorffiana peaked in 1973 

 (Table 6-4). The increase in brood size of the Daphnia suggests that food 

 supply for the Daphnia had increased, a deduction supported by a number 

 of previous studies (e.g., those on D. magna by Green (1954, 1956)). We 

 tested this with young Daphnia cultured in pond water with extra sestonic 

 particles added from the same pond. The particles were concentrated from 

 the pond water with an Amicon macromolecular filter. Seven Daphnia 

 were placed in 750 ml of water and fresh particle suspensions were added 

 daily for 1 1 days. At the end of the experiment, control flasks with no 

 added food contained animals with an average of 1.0 embryos per brood 



TABLE 6-4 Daphnia Brood Size and Biomass of Daphnia Contrasted with 

 the Biomass for the Other Crustacea in Pond D 



Biomass 

 Mean brood Biomass Daphnia + fairyshrimps Biomass 



Sample size of Daphnia only +Diaptomus bacillifer Fairyshrimps 



Year dates Daphnia /.(g C liter "^ /JgCliter"^ /igCliter"^ 



1971 7/5, 1.18 20.6 83.2 54.4 

 7/12 



1972 7/3, 3.50 264.0 312.9 3.2 



7/13 



1973 7/16 4.15 73.5 99.8 



