FISHERY BULLETIN: VOL. 71. NO. 1 



At all exposure levels the highest tissue accumu- 

 lation occurred in the first 12 hr. At 24 hr, the 

 concentrations in the green glands had shown 

 a considerable decline and then increased steadily 

 with values remaining over 10 times the ex- 

 posure level. The 48-hr determination of 280 

 ppm is based on only two samples and needs 

 verification. 



Muscle 



Muscle tissue remained almost constant over 

 the entire time of the experiment, and tissue 

 levels remained only slightly above the exposure 

 levels with maximum concentrations of 29.3 ppm 

 in crabs exposed to 25 ppm, 17.3 ppm from crabs 

 in 15 ppm, and 8.9 ppm from crabs exposed to 

 5 ppm. 



DISCUSSION 



Cadmium toxicity is related to both temper- 

 ature and salinity. The acute toxicity data for 

 crabs maintained at different temperatures show 

 a time delay in the onset of the lethal eflfect of 

 cadmium. Whether this delay is due to differ- 

 ences in bioaccumulation rates or to differences 

 in a temperature-dependent metabolic response 

 to the metal remains to be examined. Fiddler 

 crabs are often exposed to temperatures well in 

 excess of 30°C, and higher temperatures would 

 further accentuate the toxic effects of small 

 amounts of cadmium. 



There is a clear relationship of high suscep- 

 tibility of fiddler crabs to cadmium in a low- 

 salinity water. It has not been determined if 

 this is due to interaction between the metal and 

 the variety of salts in the seawater resulting 

 in a nontoxic precipitate forming in proportion 

 to the salinity (Bryan, 1971) or if the direction 

 of the osmotic gradient in the higher salinities 

 reduces the rate of entry of the metal. 



The rapid accumulation of cadmium from the 

 surrounding water results in considerable tissue 

 destruction in the first 24 hr. High concentra- 

 tions of cadmium were found in the gills and 

 hepatopancreas of fiddler crabs. Similar results 

 have been reported in Crustacea exposed to zinc 



and mercury (Bryan, 1966; Vernberg and Vern- 

 berg, 1972) although high metal concentrations 

 in the green glands were not reported for these 

 metals. Gardner and Yevich (1970) reported 

 gill tissue destruction in the mummichog begin- 

 ning after 20 hr exposure to cadmium. The data 

 presented here for Cd"""^ concentrations in fiddler 

 crab gills indicate that 24 hr is the time when 

 the cadmium content in crabs exposed to high 

 Cd^^ concentrations is reduced by tissue destruc- 

 tion. Yager and Harry (1966) showed a de- 

 crease in cadmium concentration in the liver of 

 snails exposed to high concentrations of cadmium 

 but attributed this decline to individual varia- 

 tion rather than to tissue destruction. 



Mount and Stephan (1967) suggested that 

 there is a threshold concentration of cadmium 

 in the gill tissue of fishes and that death occurs 

 when this concentration is exceeded. This 

 threshold may be around 110 ppm for fiddler 

 crabs. 



The relationship between cadmium toxicity 

 and temperature and salinity variation illus- 

 trates that physiological stresses, even within the 

 usual ecological range experienced by the ani- 

 mals, lowers the tolerance of organisms to en- 

 vironmental pollutants. 



ACKNOWLEDGMENTS 



I wish to express thanks to Mrs. Barbara 

 Caldwell and Mrs. Cary Clark for their techni- 

 cal help and to Dr. Winona B. Vernberg for her 

 support and advice on the preparation of the 

 manuscript. This study was supported by the 

 Belle W. Baruch Coastal Research Institute, Uni- 

 versity of South Carolina. 



LITERATURE CITED 



American Public Health Association. 



1971. Standard methods for the examination of 

 water and wastewater, including bottom sediments 

 and sludges. 14th ed. Am. Public Health Assoc, 

 N.Y., 874 p. 

 Ball, I. R. 



1967. The toxicity of cadmium to rainbow trout 

 (Salmo gairdnerii Richardson). Water Res. 1: 

 805-806. 



152 



