VERNBERG and VERNBERG: SURVIVAL AND METABOLISM OF FIDDLER CRAB 



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Figure 5. — Oxygen uptake rates of male and female 

 Uca pugilator maintained at 5° in 5%o seawater with and 

 without the addition of 9 X 10-^ m HgClg or 0.18 ppm. 

 The vertical bar through each mean value is the standard 

 error. 



DISCUSSION 



Fiddler crabs are capable of rapidly removing 

 mercury from their surrounding aqueous media 

 and retaining it in their tissues. However, not 

 all tissues concentrate mercury to the same de- 

 gree. The rapid accumulation and large con- 

 centration of mercury in gill tissue of fiddler 

 crabs and the lesser but significant amounts of 

 mercury found in the hepatopancreas and green 

 gland are similar to results obtained in experi- 

 ments involving other heavy metals. Bryan 

 (1966), for example, found the highest concen- 

 tration of zinc in the gills and hepatopancreas. 

 He related these concentrations to the fact that 

 excess zinc can be stored in the hepatopancreas 

 in the crab Carcinus maenus and concentrated 

 and excreted across the gills. 



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Figure 6. — Oxygen uptake rates of male and female 

 Uca pugilator maintained at 35°C in 5%c seawater with 

 and without the addition of 9 X 10-7 m HgClg or 0.18 

 ppm. The vertical bar through each mean value is the 

 standard error. 



Uca pugilator can adapt quickly to a wide 

 range of adverse environmental fluctuations 

 (Vernberg and Vernberg, 1970). The sudden 

 changes in temperature and salinity that do oc- 

 cur usually do not persist for prolonged periods 

 of time, and conditions usually ameliorate with- 

 in a week or two. Results presented in this pa- 

 per indicate that the crabs can withstand low 

 salinity and high temperature better than low 

 salinity coupled with low temperature, findings 

 consistent with the earlier generality proposed 

 byPanikkar (1940). Further, Lockwood (1962) 

 stated that since ionic regulation is thermally 

 influenced, organisms survive dilute medium 

 more successfully when the rate of ion uptake 

 as compared with ion loss increases faster with 

 increasing temperature. Under both sets of 

 conditions, however, the added stress of con- 

 centrations of mercury that are sublethal under 

 optimum conditions adversely aflfected survival 

 rates under stressful conditions and more mark- 

 edly in males than in females. Bryan (1971) 

 has speculated that the increased lethality of a 

 heavy metal under stressful conditions is in some 

 way related to changing rates of absorption. 

 Our data are another example of the principle 



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