FISHERY BULLETIN: VOL. 70, NO. 2 



that multiple environmental factors, each at a 

 sublethal level, interact synergistically to cause 

 death. Earlier papers, especially the classic 

 paper of McLeese (1956), emphasized the lethal 

 role of "normal" environmental factors, whereas 

 we have demonstrated the importance of pollut- 

 ants as part of the "normal" environment of 

 many species. 



Under optimal conditions of temperature and 

 salinity mercury generally decreased metabolic 

 rates of the males; effect on metabolic rates of 

 females was much less pronounced. This dif- 

 ferential effect of mercury on the metabolism 

 of males and females is difficult to understand. 

 On an interspecific basis, differences between re- 

 sistance of larvae oi Artemia salina and Elminius 

 viodestus to mercury have been related to dif- 

 ferences between rates of uptake rather than of 

 tissue resistance (Corner and Rigler, 1958). 

 However, since the amount of mercury in tissues 

 of both male and female fiddler crabs was essen- 

 tially the same, these differences would not ap- 

 pear to be related to differences in uptake of the 

 mercury. Under conditions of thermal and sa- 

 linity stress without the addition of mercury 

 the metabolic rate of the female crabs tended 

 to be more stable and less depressed than the 

 rate of male crabs. The addition of mercury 

 to the already stressful conditions accentuated 

 these differences. 



Our results indicate, then, that a concentration 

 of mercury that is sublethal under optimum con- 

 ditions of temperature and salinity, may greatly 

 reduce the ability of the population to survive 



under normally stressful conditions of temper- 

 ature and salinity flux. 



ACKNOWLEDGMENTS 



We are grateful to Ms. Gary Clark and Ms. 

 Barbara Caldwell for technical assistance and to 

 Dr. Lamar Priester of the State Board of Health 

 for mercury analyses, 



LITERATURE CITED 



Bryan, G. W. 



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420 



