eT
—_
ee
Usually the crab carapace was prepared for ashing without any attempt to scrub or scrape
the surface. In one instance, however, one-half the carapace was prepared as usual, whereas
small amounts of algae and unidentified material were scraped from the surface of the other
half. These scrapings were found to have a specific activity more than ten times that of the
carapace as a whole (150,000 compared with 14,000 d/m/g). When the amall proportion of the
total weight of the carapace represented by the surface material is considered, it is clear that
little, if any, of the radioactivity was actually deposited in the exoskeleton.
A similar situation was found with clam shell, where material scraped from the surface
had a specific activity 68 times that of a portion of the shell taken as a whole (6800 compared
to 100 d/m/g). In this case the surface material makes up an even smaller proportion of the
total weight than it does in the crab carapace.
Contamination of the skin of a species of sea cucumber, #, afra, is evident from a com-
parison with a second species, Stichopus sp., collected at Aaraanbiru (Table 4.22). A total
of nine specimens was collected in 4 to 7 {t of water within an area of less than 1000 ag ft.
The two species live side by side and are both detritus feeders. H. atra, however, have a habit
of coating themselves with sand, whereas Stickopus do not. Even though the former were washed
and scrubbed with the hand at the time of collection, it is clear that the specific activity of
their body wall, which includes the skin, is higher. That this is due to surface contamination
is further substantiated by the greater individual differences in the specific activity of the
body wall of H. aira.
Table 4.22 —-COMPARISON OF RADIOACTIVITY OF TWO SPECIES OF SEA
CUCUMBERS COLLECTED AT AARAANBIRU, POSTSHOT*
H, atra
Body wall
Stichopus sp.
Gut and contents
“Body wall
Gut and contents
140
230
17
64
4600
1100
5800
6800
8.5
5.4
1.2
6.1
5.4
2600
5800
4400
4200
3600
Av. 110
4600
6.5
5200
* Measured in disintegrations per minute per gram (x 1000), wet
sample.
The degree to which the food habit affects the specific activity of the digestive tract and its
contents is found in a comparisonof the viscera of a pistol shrimp, Crangon sp., and a bluegreen alga, Lyngbya sp., which are intimately related ecologically. Two specimens of shrimp
were found, one at Rigili and one at Runit, living in a completely closed cylinder of the living
algae. The cylinders had to be torn open in order to remove the shrimp. A similar, if not the
same, association was reported by Taylor® with specimens from Rongerik and Bikini Atolls in
the Marshall Isiands. This shrimp feeds, at least in part, upon the algae in whichit lives. It
may, however, be omnivorous since a similar Pacific Coast species is known to stun prey with
the .{olent snapping of a specialized claw, hence the name “pistol shrimp.” It is difficult to
conceive how, living encased in a cylinder of highly enmeshed filaments of algae, it could feed
on anything larger than very small plankton, if that, in addition to the algae. The similarity
of the specific activities found in the viscera of the shrimp and in the algae, as shown in
Table 4.23, indicates the effect of food habit upon the radioactivity of the digestive tract.
80
~ UNCLASSIFIED
hides
Ra
wt