Land Crabs and Fission Products~~HELD 
23 
Fig. 4. Decay of beta-activity in three Coenobita carapace samples, each compared with the theoretical 
decay curve (solid lines) for Sr 89 + Sr 90 from Figures 2 and 3. 
ten times that in land plants on a wet weight 
basis and is more than three times that in soil 
on a dry weight basis. 
Muscle 
Isotopes with half lives greater than 20 years 
contributed nearly all of the activity in muscle 
tissue 35 days before the Nectar test. Cs 137 , 
Sr 90 + Y 90 , and Ce 144 + Pr 144 accounted for 
84, 10, and 1 per cent respectively, of the total 
activity in muscle tissue collected in February 
and November, 1955, and analyzed in January 
and March, 1956. Similar levels, 67, 10, and 1 
per cent, were found in coconut crab muscle 
from Rongelap Atoll (UWFL-43, table 14). In 
contrast to the exoskeleton, muscle tissue had a 
variable, though generally decreasing, level of 
long-lived isotopes throughout the post-Nectar 
collecting period (Fig. 6). Between 150 and 
200 days post-Nectar, the total activity in muscle 
was due primarily to the long-lived isotopes, 
as evidenced by the increased ecological half 
life. The level of total activity in muscle at 172 
days (after Nectar) is one-sixth the pretest 
level, while the level of long-lived isotopes at 
that time is one-eighth that of the pretest level; 
subsequently there is an increase in activity. 
Since both the total activity and the long-lived 
activity increased by approximately equivalent 
amounts, the increase must be due to an in- 
creased net rate of uptake, reflecting a change 
in the physiology of the crab or a change in the 
TABLE 1 
Total /?- Activity and Sr 90 + Y 90 in Coenobita 
Carapace 
(Determinations made in January and February, 1956. 
Averages of three samples and their standard errors 
are given.) 
DATE 
COLLECTED 
TOTAL 
/? -ACTIVITY 
JAN.-FEB., 
1956 
d/m/g wet 
Sr 90 -}- Y 90 
ACTIVITY 
FEB., 1956 
d/m/g WET 
4/15/54 
6900 it 672 
7454 ± 952 
5/26/54 
10243 fc 968 
9763 ± 975 
8/12/54 or 
14851 ± 1413 
15568 ± 1237 
8/19/54 
10/5/54 
4362 ± 431 
4043 ± 385 
3/15/55 
10368 ± 581 
11281 ± 479 
2/9/55 
12516 ± 1594 
12532 ± 1484 # 
* Average of duplicate aliquots of three pooled samples as 
determined by Dorothy J. South, Applied Fisheries Laboratory. 
