FISHERY BULLETIN: VOL. 70, NO. 2 



0' 



10 



20 



g 30 



^ 40 



i 50 



t 60 - 



O 



2 70  



80 - 



90 - 



• •Control females 



o o Experimental females 



• •Control moles 



o o Experimental moles 



14 

 DAYS 



22 



Figure 3. — Mortality of Uca pugilator in h'/ir seawater 

 at 35 °C with and without the addition of 9 X 10-7 m 

 HgCla (0.18 ppm Hg). 



METABOLIC EFFECTS 



Although a low level concentration of mercury- 

 was not lethal to the crabs under optimum envi- 

 ronmental conditions, metabolic rates of these 

 crabs were affected, especially those of males. 

 Initially, metabolic rates were established for 

 both males and females at 25°C in 30%. seawater, 

 and the rates for males and females were essen- 

 tially the same (Figure 4). After the base-line 

 rate was determined, the same animals were then 

 maintained at 25 °C in ^O'/ic seawater with the 



200 



X 



» 



2 

 < 



O 

 UJ 



a. 



100 

 80 



60 

 40 



(ft 



UJ 



20 



tFemoles I 

 " 1 



J L 



I 3 7 



II 14 17 

 DAYS 



21 



28 



Figure 4. — Oxygen uptake rates of male and female 

 Uca pugilator maintained in 30%r seawater containing 

 9 X 10-7 M HgCla (0.18 ppm) at 25°C. The base-line 

 rate is represented by the first set of data points on the 

 left. The vertical bar through each mean value is the 

 standard error. 



addition of mercury, and metabolism of the crabs 

 was determined periodically for 28 days. The 

 metabolic rate of the males remained essentially 

 unchanged through day 3. By day 7, however, 

 the metabolic rate had dropped to 32% of that 

 of untreated crabs ; by day 21 the rate had de- 

 creased by 48%; and by day 28 the rate was 

 20% lower than the base-line value. In the fe- 

 male, oxygen uptake values also decreased by 

 day 7, but by day 14 the metabolic rate returned 

 to the base-line rate and remained essentially 

 at this level through day 28. Although initially 

 the same, the rate of oxygen uptake of males 

 was significantly lower than that of the females 

 after 21 days in this sublethal concentration of 

 mercury, and the metabolic rate of the males 

 had not returned to the same level as it was be- 

 fore the crabs were placed in mercury by the 

 end of the 28 day experimental period (Figure 

 4) . Both males and females, however, continued 

 to survive for another month under the same 

 mercury regime as before without any signifi- 

 cant increase in mortality. 



Under conditions of low temperature (5°C) 

 and salinity (5%p) stress, not only did females 

 survive much longer than males, but also the 

 females were better able to maintain a steadier 

 rate of oxygen uptake (Figure 5). The metab- 

 olic rate and pattern of the experimental female 

 crabs were similar to those of the control female 

 crabs. The metabolic rate of male experimental 

 crabs was not significantly different from that 

 of the female experimental or male and female 

 control crabs, after a 1-day exposure to mercury, 

 but by day 3 the rate dropped markedly (Fig- 

 ure 5). 



Oxygen uptake rates of female control crabs 

 maintained in low-salinity water {^'/u) and at 

 high temperature (35°C) were relatively con- 

 stant over a 28-day period and tended to be 

 higher than that of control male crabs (Figure 

 6) . The metabolic rates of experimental female 

 crabs remained fairly constant for the first 7 

 days and then declined rapidly. The uptake rates 

 of experimental male crabs declined steadily 

 from day 1 and tended to be lower than those 

 of the females throughout the remainder of the 

 time period (Figure 6). 



418 



