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Invertebrates
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Rongelap invertebrates showed levels of activity of from
10 = to 104 uc/kg on March 26, 195%.
By late January 1955 the
levels had dropped about two orders of magnitude.
The almost
ubiquitous black sea cucumber, Holothuria atra, serves best to
exemplify the trend (Figure 6).
Next best as indicators were
giant clams, Hippopus and Tridacna; land hermit crab, Coenobita;
coconut crab, Birgus; corals; and spider snail, Pterocera.
Radioactivity was highest in the digestive and excretory organs,
intermediate in the integumentary organs, and lowest in the
Appendix.
Actual values for the samples are tabulated in the
The kidney of the giant clam (Figure 7) 1s of special
interest because of its high level of activity and slow rate of
decline.
A graph of activity of the tissues of lend hermit
crabs collected at the more radioactive northern islands in
March and July 1954, and from a less radioactive southern island
in January 1955, shows the effect of geographical differences in
radioactivity upon the trend of decline, accentuating the slope
in the later period (Figure 8).
The spider snail was similar
to the hermit crab in the level of activity of its tissues,
while the corals were about an order of magnitude lower.
Land Plants and Algae
Land plant and algae collections were made at Labaredj,
Kabelle, Lomuilal, Gejen, and Rongelap islands.
Most of the
edible plants were collected in December 1954 and January 1955
&t Rongelap Island.
These were coconut, squash, papaya, arrow-
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