24 
PACIFIC SCIENCE, VoL XIV, January I960 
I0 6 
,I0 5 
I0 4 
d/m/g wet 
I0 3 
I0 2 
Fig. 5. Radiostrontium in Coenobita skeletons at 
Belle Island. 
conditions in the environment, leading in this 
case to a greater availability of Cs 137 to the 
crab. The latter possibility is the more easily 
explained by the observations. 
The same pattern of decrease in activity fol- 
lowed by a rise is evident in the gut and liver 
of the crab, the leaves of the shrubs, Scaevola 
and Messerschmidia, and the muscle of the field 
rat, Rat t us exulans, from Janet Island (Engebi) 
which is also in the northern part of Eniwetok 
Atoll (Lowman, MS). During the first 200 days 
(May-November, 1954) rainfall at Eniwetok 
averaged about 4 inches per month, while for 
the following 150 days ( December- April ) the 
average monthly rainfall was about 0.3 inches 
(Fig. 7). Since individual variation in the level 
of activity is great there would be little reason 
to accept the validity of the correlation were it 
not repeated in the plants and in rat muscle, 
which are also high in Cs 137 content (56 per 
cent of the total activity in the latter). It ap- 
pears likely, therefore, that the changes in ac- 
tivity in the crab and rat muscle reflect some 
underlying mechanism associated with rainfall 
which is responsible for changes in the levels of 
activity in the plants. 
There could be one or several factors in- 
39 +Sr 90 +Y 90 
1948 1952 1953 1954 1955 1956 
volved in the association with rainfall includ- 
ing, for example, such things as exchangeability 
of cesium, total amount of root surface available 
during the wet as compared with the dry season, 
and increasing acidity of the soil on drying 
(Stone, 1951)- More complete series of radio- 
chemical determinations of the radioisotopes in 
both plants and soils are needed to understand 
the mechanisms involved. Contrary to results re- 
ported on relative availability of cesium and 
strontium to plants in other soils, cesium appears 
to be more readily available than strontium in 
the atoll island soil (Selders et al 1955; Neel 
et al. , 1953; Larson et al, 1953; Nishita et al, 
1954; Ophel, 1955). 
The short half -life isotopes that contributed 
to the activity in the muscle during the first 150 
days are not known. The rate of decline during 
this period was approximately the same as the 
rate of decay for mixed fission products. 
Radiocesium content of hermit crab muscle is 
about 1.5 times that in plants (1,000 d/m/g : 
700 d/m/g) on a wet weight basis. The radio- 
cerium levels In the soil were too low ( < 1 
per cent of the total activity) to be detected by 
the radiochemical methods used. 
Hepatopancreas ("Liver”) 
The rate of decline of activity of the hepato- 
pancreas or "liver” of the crab during the first 
175 days post-Nectar is not significantly dif- 
ferent from the rate of decay of mixed fission 
products. This is true despite the fact that there 
was a pre-existing level of long-lived activity 
approximately equal to the level existing 537 
days post-Nectar. Sr 90 , Cs 137 , and Ce 144 were 
found. 
Equilibrium must be quickly reached and 
maintained at a constant level proportional 
to the availability of the long-lived Isotopes. 
Levels of activity were 8,500 d/m/g pre-Nectar, 
reached a maximum of 10 G d/m/g four days 
post-Nectar, and declined to a level of 3,000 
d/m/g at 305 days and 537 days (Fig. 1). 
Gut with Content 
The hermit crab gut with its content was gen- 
erally more variable than the liver in levels of 
activity, especially during the first month post- 
Nectar. This difference is to be expected, since 
ingested food would have variable amounts of 
