308 
Better agreement resulted from the use of geo- 
metric than from arithmetic means. 
Analysis of the table shows that the islets had 
an estimated 1.7 X 10 4 H. atra and 3.7 X 10 8 
H. leucospilota. In addition, an extensive area 
(4 X 10 4 m 2 ) of shallow (4-6 m) lagoon bot- 
tom off Island 13 and Island 15 (Fig. 1) was 
observed from a skiff to be populated with an 
estimated 10 4 30-cm black (not sand-coated) 
H . atra lying on the light sandy portions among 
the darker predominating, staghorn corals. The 
estimate for the 700 m of reef -flat north of 
Aniiru L, as far as a transverse ridge across the 
reef, was based on three traverses from 3 to 6 
m wide: first, walking north along the middle 
of the reef; then back, one-third of the way in 
from the seaward edge of the reef; and finally, 
pacing west across the reef on a line 200 m 
north of Aniiru I., for a distance of 500 m 
lagoonward from the seaward reef edge. Extra- 
polations of the above observations to the entire 
Fig. 2. Inner edge of reef-flat, Rongelap I., section 
29, showing Holothuria in pools. Sept. 5, 1959, 1025 
hr. 
PACIFIC SCIENCE, Vol. XVII, July 1963 
atoll suggest the following numbers of H. atra 
and H. leucospilota , respectively: for islet shores, 
2.5 X 10 4 and 5.5 X 10 3 ; for inter-islet reefs, 
4 X 10 6 and 10 5 ; and for shallow lagoon bot- 
tom areas, 5 X 10 5 H. atra, or a total for the 
entire atoll of 4.5 X 10° atra and 1.6 X 10 5 
leucospilota. 
OTHER SPECIES OF SEA CUCUMBERS 
Species observed other than H, atra and H. 
leucospilota are mentioned in order of decreas- 
ing abundance. Stichopus chloronotus , the green- 
ish-black prickly sea cucumber on the inter-islet 
reef-flat and on the sandy, shallow lagoon shore 
near the north channel of Kabelle I. was most 
common. Also on the shallow, sandy bottom, 
lagoonward from Kabelle I. we observed in mid- 
September 1961, during a period of extreme 
tides, a heavy concentration (about 1/m 2 ) of 
10 to 20 -cm specimens of a light-colored Ac- 
tinopyga sp. with small brown spots. Dead 
specimens were common on the lagoon shore of 
Kabelle I. The large brown Actinopyga mauriti- 
ana occupied the outer edge of the reef-flat. 
Holothuria gyrifer, a small tan-colored sea cu- 
cumber with white spots, was common under 
rocks on the seaward reef and especially in the 
channel north of Kabelle I. Occasional speci- 
mens of Ophiodesoma spectahilis were encoun- 
tered under rocks. 
SAND PASSING THROUGH HOLOTHURIA 
The holothurians have been called the earth- 
worms of the sea. The amount of sand passing 
through the gut of Holothuria is of interest 
because of the possibility of profound alteration 
of the ecology in those areas where sea cucum- 
bers are abundant. Crozier (1918) has estimated 
that in 1.7 sq miles of bottom in Harrington 
Sound, Bermuda, 500-1000 tons of sand pass 
through Stichopus moehii annually (considering 
their average length to be 27 cm and the dry 
weight of the contained sand to be 46 g). He 
concluded that the primary effect of the feeding 
habits upon the environment is the moving of 
sand from one place to another. 
Trefz (1958:14) timed the passage of sand 
through captive H. atra at about 12 hr for an 
average-sized specimen of 30 cm. Assuming an 
