Sea Cucumbers at Rongelap Atoll — Bonham and Held 
309 
Fig. 3. H. leucospilota (black) extending from 
underneath H. atra in a pool on the eastern shore of 
Rongelap I., Aug. 23, 1958, 1700 hr. 
average gut content of 100 g dry weight, this 
would be equivalent to 1 gram in 7.2 min. 
Larger specimens required more time for pass- 
age of sand through the gut than did smaller 
specimens, according to the following relation- 
ship derived from her data for specimens of 
25-38 cm (omitting two outlying observations): 
t=5.3 + 0.233 L 
where t represents time in hours for passage 
through the gut, and L is length of sea cucumber 
in cm. 
Yamanouti (1939:614) weighed the gut con- 
tents of 65 small (5-25 cm) H. atra and re- 
corded an average of 17.1 g dry weight (range, 
0.4-40.5 g). Time required for passage through 
the gut of captive specimens averaged 4.8 hr. 
Thus, 1 gram would be ingested every 16.8 min 
on the average. 
Direct observation during low, daytime tides 
of undisturbed, feeding individuals of H. atra 
30 cm long in their natural habitat at Rongelap 
Atoll showed egestion of sand at the rate of 1 
g (dry basis) in from 5 to 10 min, agreeing 
with deductions from the data of Trefz on cap- 
tive specimens. Assuming continuous feeding, at 
Rongelap Atoll the estimated 5 X 10 r> H. atra 
and H. leucospilota probably ingest and egest 
about 2.4 X 10 8 kg of sand yearly. 
It has been pointed out by Crozier (1918) 
for Stichopus moebii, by Yamanouti (1939) for 
H. atra and other species, and by Trefz ( 1958) 
for H. atra, that there is virtually no grinding 
action or reduction in size of sand particles upon 
passing through the gut. Trefz has demonstrated 
that even such minute and delicate calcareous 
structures as the integumental "anchors and 
plates” of the sea cucumber, Ophiodesoma spec- 
tabilis, do not undergo perceptible dissolution 
in the gut of H. atra, but that they appear the 
same after egestion as before ingestion, thereby 
negating the idea of chemical dissolution in the 
gut. 
In some of the scoured depressions on the 
seaward reef where very little sand is present, 
H. atra serves an additional function by retain- 
ing within and around itself much of the sand 
required in its feeding that might otherwise be 
washed away. 
SIZE OF SPECIMENS 
The length of undisturbed H. atra in the open 
ranged from about 2 to 60 cm, with estimated 
weights of 10 to 2000 g. We have not observed 
smaller ones. Frequent estimates of length dur- 
ing the censusing led to the opinion that the 
geometric mean length of H. atra on the islet 
shores is about 17 cm and of the more slender 
H. leucospilota about 25 cm. In contrast to the 
elongate shape of the larger specimens, the 
smaller specimens of H. atra were short and 
thick; in fact, the smallest (2 cm) were as thick 
as they were long. At the northeastern reef of 
Kabelle I. on September 14, 1961, 407 speci- 
mens of H. atra in a single pool were individ- 
ually measured or estimated for length and 
diameter in inches, while still undisturbed, 
and were then placed in a container of water 
for volume measurement in cm 3 by displace- 
ment. The temperature of the pool ranged 
from about 35 to 39 C during the 5 hr re- 
