o 



O 

 O 



150 



LU 



O 



cr 



UJ 

 Q. 



liJ 



100 



§ 



50 _ 



o 



5p.p.t. 



50p.p.t. — ' — 

 100p.p.t. 



-150p.p.t. 

 -200p.p.t. 



^--.^ 1-... 



"^-, 



--2 



1 



1 



1 



20 40 60 



DOSE(klLORADS) 



80 



Figure 27. — Comparison of the respiration rates of irradiated brine shrimp nauplii at different salinities plotted as 

 percentage of control respiration rates. Vertical lines represent +1 standard error for four replications. 



the ability of brine shrimp to osmoregulate by 

 inhibiting the transport of ions by the organelles 

 in the branchiae ("gills"). The increase in 

 respiration that we observed in irradiated 

 nauplii at salinities of 100 and 150 p.p.t. was 

 similar to that shown by nauplii exposed to the 

 metabolic inhibitor 2,4-dinitrophenol. In addi- 

 tion to an increased rate of respiration, the 

 internal sodium concentration of the meta- 

 bolically inhibited nauplii increased at salini- 

 ties approaching 100 p.p.t. --the point at which 

 we first found increased respiration inirradi- 

 ated nauplii. This increase in internal sodium 

 could be caused by decreased active transport 

 of sodium ions outward. From the similarity 

 between results obtained with radiation and 

 2,4-dinitrophenol, the assumption might be 



made that radiation also inhibits ion trans- 

 port. If this assumption is correct, the radi- 

 ation-sensitive site in the nauplii may be 

 metabolically active organelles in the bran- 

 chiae, which act in the metabolic transport 

 of salt. If radiation impairs the ability of 

 the nauplii to transport ions actively, the in- 

 creased respiration rates at 150 p.p.t. salinity 

 might reflect the additional metabolic work 

 required for the nauplii to maintain their salt 

 balance. The decreased respiration rates of 

 irradiated nauplii at 200 p.p.t., however, seem 

 to conflict with the idea that increased res- 

 piration rates reflect the inhibition of active 

 outward transport of salt. We observed that 

 irradiated nauplii were unable to survive in 

 200 p.p.t., possibly because they are unable to 



51 



