330 M. Butler etal. 



production undoubtedly occurred in early September. In some years, 

 snowstorms or very low temperatures in August can kill most of the 

 adults. 



Egg mass produced was considerable and made up as much as 35% of 

 the total weight of a small animal. Most of the eggs were not released and 

 the increase in eggs beneath the carapace merely increased the biomass 

 (Column A in Table 7-5). The mass of eggs actually released was only 

 6.2% of the total net production. 



Another 24% of total production was calculated from the exuviae 

 given off and from the mortality that occurred before the end of the 

 season. Because of the 24 to 30 molts that take place during growth, the 

 exuviae represent a major loss of carbon (15%) while the mortality is only 

 9% of total production. Most of this mortality occurs in the younger stages 

 when the density of animals falls from 30 to 2 m ~ " . 



During the cold summer of 1973, Lepidurus appeared to respire only 

 33% of assimilated carbon, an extremely high yield indeed. Assimilation 

 was the sum of net production plus respiration (Table 7-5). Respiration 

 was calculated from mean daily temperatures, biomass estimates and data 

 (Figures 7-14 and 7-15) on respiration rates for different temperatures and 

 body weights (see Kallendorf 1974 for details). Of course, this yield of 67% 

 is possible only because the temperature during 1973 was mostly below 

 10°C. Also, as noted, the Gilson measurements may be too low as this is 

 normally an active animal. 



Even if there is some error in the respiration measurements, the 

 growth efficiency of the tadpole shrimp must have been high in order to 

 produce such rapid growth. In 60 days, animals grew from a small egg (33 

 ^lg C) to a 25-mm adult (6800 ^lg C). The efficiency of close to 70% is very 

 high compared with other aquatic crustaceans (Table 7-6) such as Hyalella 

 (15 to 22%) and Leptodora (8%). The laboratory population of 

 Simocephalus and the Chironomus in the ponds at Barrow did approach 

 this efficiency. 



The total carbon flux through this animal is extremely small (17 mg 

 m~"yr~') and would be small even if any respiration error were corrected. 

 This may be due in part to the very low density of Lepidurus during 1973. 

 On the other hand, the importance of a top carnivore such as this to the 

 ecosystem is usually not reflected in the rate that it processes food. 



Food Sources and Ingestion 



In the planktonic form the nauplii of Lepidurus are only a little larger 

 than Daphnia; yet they are not effective filter feeders. When the clearance 

 rate was measured with H'^COs-labeled algae and glucose- '^C-labeled 

 bacteria, the results of 0.16 ml hr ' and 0.10 ml hr \ respectively, were 

 very low for a 1 .96 mm Lepidurus. Large Daphnia (2.0 mm) clear up to 3.4 



