VERNBERG and VERNBERG: SURVIVAL AND METABOLISM OF FIDDLER CRAB 



RESULTS 



MERCURY UPTAKE BY TISSUE 



Mercury was not detected in the untreated 

 seawater, although there were detectable traces 

 of mercury found in the Clark's fish pellets fed 

 to the crabs. The hepatopancreas of the control 

 animals (animals collected in the same region as 

 experimental animals and maintained in sea- 

 water without mercury addition) had approxi- 

 mately 0.03 ppm mercury, but no mercury was 

 found in any of the other tissues. Within the 

 first 24 hr after exposure to 30%c seawater at 

 25 °C containing an initial concentration of 

 0.18 ppm mercury, however, gill tissue contained 

 1.73 ppm mercury; the amount of mercury in 

 this tissue increased steadily with continued ex- 

 posure (Figure 1). Of the five tissues assayed 

 for mercury content, gill tissue was found to 

 have the highest concentration. Mercury also 

 accumulated in the hepatopancreas and green 

 gland although much less rapidly and at a lower 

 concentration level (Figure 1). Lower amounts 

 of mercury were found in abdominal muscle tis- 

 sues and in the carapace; after 28 days exposure 

 to water containing mercury, levels were approx- 

 imately 1 ppm. 



28 



DAYS 



Figure 1. — Mercury in tissues of Vca pugilator after 

 exposure of the crabs to 9 X lO-^ m HgCla (0.18 ppm 

 Hg) in 30%o seawater at 25 °C for varying lengths of 

 time. 



• • Control females 



-~^ o o Experimentol females 



• Control moles '~ 



o Experimental moles 



18 20 22 24 26 



Figure 2. — Mortality of Uca pugilator in b%c seawater 

 at 5° C with and without the addition of 9 X 10"'' 

 M HgClg (0.18 ppm Hg). 



LETHAL LEVELS 



Preliminary studies established that under 

 optimum conditions of temperature (25 °C) and 

 salinity (30^r) the crabs could survive for pro- 

 longed periods of time (at least 2 months) in sea- 

 water having an initial concentration of 9 X 10"'^ 

 M HgCl2 (0.18 ppm mercury). Under tempera- 

 ture and salinity stress, however, this concentra- 

 tion of mercury significantly shortened survival 

 time. For example, under conditions of low tem- 

 perature (5°C) and low saHnity (5%f), such as 

 could occur following heavy winter rains, the 

 crabs could not survive as long as under condi- 

 tions of high temperature and low salinity. In 

 winter animals without the added stress of a 



pollutant, 50 y<? 



C>i 



of the females survived 21 days 



but 50% of the males were dead within 7 days. 

 Under the same temperature and salinity con- 

 ditions with the addition of 0.18 ppm mercury, 

 males survived 6 days, but 50% of the females 

 died by day 8 (Figure 2). Under conditions of 

 low salinity (5%o) and high temperature (35°C), 

 conditions very apt to occur following the heavy 

 rains associated with a summer hurricane, both 

 male and female U. pugilator can survive with 

 very little mortality for at least 28 days (Fig- 

 ure 3) . With the addition of 0.18 ppm mercury, 

 however, survival times of both males and fe- 

 males are reduced. Under conditions where 

 crabs were maintained at this high temperature 

 and low salinity in water containing mercury, 

 50% of the males had died by day 17, while 

 50% of the females survived to day 26 (Fig- 

 ure 3). 



417 



