THE SYNERGISTIC EFFECTS OF TEMPERATURE, SALINITY, AND 



MERCURY ON SURVIVAL AND METABOLISM OF THE 



ADULT FIDDLER CRAB, UCA PUGILATOR' 



Winona B. Vernberg and John Vernberg- 



ABSTRACT 



Gill tissues of fiddler crab, Uca pugilator, were the major site of mercury concentration; 

 lesser amounts accumulated in the hepatopancreas and green gland. Very small amounts 

 were found in the carapace and muscle tissue. No significant differences in the amount 

 of mercury in tissues of males and females were found. 



A concentration of mercury sublethal to fiddler crabs under optimum conditions of 

 temperature and salinity greatly reduced survival times when crabs were placed under 

 conditions of temperature and salinity stress. Males were more susceptible to the 

 synergistic effects of mercury in combination with environmental stress than were 

 females. 



Metabolic rates of male and female fiddler crabs were affected by prolonged exposure 

 to mercury both under optimum environmental conditions and under temperature and 

 salinity stress. Metabolic rates of males were more adversely affected than those of 

 females. 



Estuaries are an extremely important part of 

 the marine environment. Yet often an estuary 

 becomes so grossly polluted that much of the 

 biota is destroyed before it is recognized that the 

 quality of water affects the biology of such an 

 area. Part of the problem is the subtleness of 

 the effects of sublethal concentrations of man- 

 introduced pollutants. In low concentration the 

 pollutant may have no observable effect on a 

 given population of animals if environmental 

 conditions remain at an optimum. However, 

 when another environmental parameter becomes 

 stressful, it may synergistically interact with the 

 sublethal concentration of pollutant and the or- 

 ganism dies. Many estuaries are polluted, and 

 since one of the chief characteristics of estuaries 

 is the rather extreme environmental fluctuations 

 that occur throughout the year, knowledge of 

 synergistic interaction on estuarine animals is 

 important in the preservation of estuarine eco- 

 systems. 



' This study was supported by Grant No. 18080 FYI 

 from the U.S. Environmental Protection Agency. 



^ Belle W. Baruch Coastal Research Institute and 

 Department of Biology, University of South Carolina, 

 Columbia, SC 29208. 



Manuscript accepted December 1971. 



FISHERY BULLETIN: VOL. 70. NO. 2, 1972. 



This study was undertaken to determine the 

 effect of a sublethal concentration of mercury 

 on the metabolism of adult male and female fid- 

 dler crabs, Uca pugilator (Bosc), maintained 

 under optimum and stressful conditions of tem- 

 perature and salinity, and the synergistic effects 

 on survival of this species with sublethal con- 

 centration of mercury in combination with sa- 

 linity and thermal stress. This species was se- 

 lected because it is one of the more abundant 

 and ecologically important species in an estu- 

 arine ecosystem. 



MATERIALS AND METHODS 



Crabs used in this study were collected in the 

 Georgetown, S.C., area during the fall and 

 winter months. After collection the animals 

 were brought into the laboratory where they 

 were maintained in plastic boxes containing a 

 thin layer of seawater having a salinity of ap- 

 proximately 30/'ff. All crabs were kept in con- 

 stant temperature boxes at 25°C and on a 12-hr 

 light-dark photoperiod for at least 2 weeks. 

 Crabs were fed on Clark's fish pellets every third 



415 



