compensate for the inhibition caused by radi- 

 ation and succumb to the additional physio- 

 logical stress imposed when they attempt to 

 maintain their homeostasis against the greater 

 osmotic gradient. 



Brine shrimp nauplii were affected most by 

 the interaction of radiation and salinity when 

 they were held in salinities approaching those 

 of their natural habitat. The highest salinity 

 used in these experiments was well within the 

 tolerance range of the brine shrimp and, based 

 on estimates of lethal doses of radiation for 

 adult brine shrinip (186,000 rads of X-ray for 

 males and 140,000 rads for females), the nau- 

 plii also should have survived naost of the 

 radiation doses used. We found, however, that 

 at 200 p.p.t. salinity and after radiation doses 

 of 20,000 rads or greater, the nauplii appeared 

 to be under a severe physiological stress and 

 did not survive long. 



THE INFLUENCE OF SALINITY AND 



TEMPERATURE UPON THE RESPIRATION 



OF BRINE SHRIMP NAUPLH 



David W. Engel and Joseph W. Angelovic 



Historically the brine shrimp has been cate- 

 gorized as one of the most adaptable aquatic 

 invetebrates. Its ability to adapt to a wide 

 range of salinities and temperatures has made 

 it the dominant species in such rigorous en- 

 vironments as Great Salt Lake, Utah. The 

 ability of brine shrimp to survive in salinities 

 of 10 to 220 p.p.t. and temperatures of 10° to 

 35° C. has been examined through observation 

 of the respiration rates of nauplii at different 

 salinities and temperatures. Results of these 

 investigations are contradictory; some investi- 

 gators have demonstrated an increase in res- 

 piration rates with increased salinity, and 

 others have demonstrated a decrease; still 

 others have found no effects of salinity on res- 

 piration rates. The purpose of this investiga- 

 tion was to determine whether temperature 

 and salinity affect the respiration rates of 

 brine shrimp nauplii from the Great Salt Lake 

 stock. 



Methods 



The brine shrimp nauplii were hatched in 

 30 p.p.t. sea water, immediately transferred 

 to sea water of 5, 50, 100, 150, and 200 p.p.t. 

 salinity, and allowed to acclimate overnight 

 at 10° C. All salt solutions were made from 

 a commercial sea-salt mixture, the composi- 

 tion of which is similar to Great Salt Lake 

 brine. 



After acclimation, aliquots of animals and 

 water from the various salinities were trans- 

 ferred to Warburg-type respiration flasks. 

 Each flask contained 3.0 ml. of animals and 



water and 0.5 ml. of 20 percent KOH in the 

 side arm. All determinations of respiration 

 rates were conducted on a differential res- 

 pirometer, and the flasks were shaken 80 times 

 per minute. Determinations of respiration were 

 made for 1 hour at temperatures of 10°, 15°, 

 20°, 25°, and 30° C. The temperature of the 

 water bath was increased 5° C. over a 15- 

 minute period between each respiration deter- 

 mination. Respiration rates, Q02 values, were 

 calculated as ^l.Oj/mg. dry weight/hour. The 

 QjQ values were calculated from Q02 values 

 for each 5 C. increase in temperature by 

 using the van't Hoff equation. 



Effects of Temperature, Salinity, and 

 Temperature-Salinity Interactions 



Respiration rates of brine shrimp nauplii 

 decreased with increasing salinity at all five 

 temperatures tested (fig. 28). A good linear 

 relation existed between temperature and the 

 respiration rates at each salinity, as shownby 

 the correlation coefficients for each of the re- 

 gression lines. The change in Q09 per unit 

 change in temperature--the slopes"of the re- 

 gression lines--decreased with increased sa- 

 linity (0.89 at 5 p.p.t., 0.76 at 50 p.p.t., 0.77 at 

 100 p.p.t., 0.54 at 150 p.p.t., and 0.43 at 200 

 p.p.t.). To determine if the differences among 

 the slopes of the regression lines were real, 

 we assumed that the respiration rates at each 

 temperature were distributed normally and had 

 equal variances. The data were tested by an 

 analysis of convariance which showed that the 

 slopes were significantly different (P<0.01). 

 The relation demonstrated by these data- -that 

 increased salinity causes reduced respiration 

 rates inbrine shrimp nauplii--supports earlier 

 findings where salinities of 10 to 50 p.p.t. were 

 used. Contrary to our results, however, those 

 earlier data showed a decrease in respiration 

 with increased temperature from 14° to 22° C. 

 Other investigators have been unable to find 

 a significant effect of salinity on the respira- 

 tion of brine shrimp nauplii at salinities up to 

 90 p.p.t. 



The metabolic rates of the nauplii at the 

 five salinities tested in the present experi- 

 ments approached zero between 5 and 8 C. 

 If it is assumed that the relation between 

 temperature and Q02 described by the regres- 

 sion equation holds true below 10° C., then the 

 lines intercept the abcissa between 5° and 8° C. 

 When the water temperature in Great Salt Lake 

 falls below 6° C., adult brine shrimp are no 

 longer found and nauplii do not appear in the 

 spring until the temperature returns to 9° C. 

 Thus, the results of our experiments are com- 

 patible with observations on the temperatures 

 at which adult brine shrimp disappear and 

 nauplii reappear in Great Salt Lake. 



The Q.Q values for the brine shrimp nauplii 

 were not directly related to the salinity of the 



52 



