An Ecological Perspective of Marcus Island, with 
Special Reference to Land Animals 
Shoichx F. Sakagami 1 
Marcus IS A small, remote reef island in the 
vast western Pacific. It is located at N. 24° 
20', E. 154° (Bryan, 1903), being 1,000 km. 
ENE. of Farallon de Pajaros (the northernmost 
of the Mariana Islands), 1,300 km. E. of Iwo 
Jima, and a little farther WNW. of Wake 
(Gressitt, 1954). 2 Prior to World War II the 
island was a Japanese dependency. Now it is 
a part of the Trust Territory of the United 
States, but there is no active establishment upon 
it except for a weather station belonging to 
the Central Meteorological Observatory of To- 
kyo. Through the courtesy of the Observatory, 
I had an opportunity to visit the island, together 
with Dr. N. Kuroda of the Yamashina Orni- 
thological Institute (birds) and Mr. M. Ya- 
mada of our Institute (marine invertebrates), 
during April 30 to May 6, 1952, and to observe 
its land biota. Although our observations were 
not extensive because of lack of sufficient time, 
I believe that the results are worth publishing 
because of our scanty knowledge of the ecology 
of the smaller Pacific islands and the lack of 
comprehensive biological research on this is- 
land since Bryan’s visit in 1903. 
TOPOGRAPHY AND SOIL TEXTURE 
Marcus Island is a raised atoll formed on an 
elevation of submarine mountains in northern 
Micronesia. As seen in Figure 1, it is triangular, 
with south and north shores of about 2 km., 
and the northwest shore a little longer. The 
1 Contribution No. 486 from the Zoological Insti- 
tute, Faculty of Science, Hokkaido University, Sap- 
poro, Japan. Manuscript received March 19, 1959- 
2 Location of the island differs slightly from one 
record to another: N. 24° 17' 30", E. 153° 58', ac- 
cording to the notification by the Tokyo Prefectural 
Office (1898); and N. 24° 17' 35", E. 154° 4' 30", 
and N. 24° 17' 02", E. 154° 1', respectively, accord- 
ing to observations by two Japanese cruisers, the 
Kasagi and the Takachiho ( Yoshida, 1902) . 
lagoon between the island and the fringing reef 
is about 200 m. on the NW. shore but is much 
narrower on the S. and E. shores ( Fig. 2 ) . All 
of the shores are lined by sandy beaches, ex- 
cept at the northernmost parts of the NW. coast, 
where the old, already mineralized reef occurs 
along the beach (Figs. 1, 3). The reef is con- 
nected with the outer ocean by means of two 
indentations in the E. and S. shores, respectively. 
Only the southern indentation is used, however, 
as the harbor for landing by boats (Fig. 1 c) , 
as large ships cannot approach the harbor be- 
cause of the dangerous underwater reef. The 
island is very flat. Formerly, the highest altitude 
was reported as 22 m. by Bryan (1903), but 
now, because of the leveling undertaken during 
the war, it is only 7 m. near the northern cape. 
Also, the trace of an old lagoon discovered by 
Bryan was filled up with earth by the wartime 
activities (Matsubara, private communication 
to the writer). A runway of about 1,700 m. 
running across the island parallel with the NW. 
shore and a broad road near the southern shore 
now divide the island into three areas, the NW. 
zone, the S. zone, and the E. triangle ( Fig. 1 ) . 
As previously mentioned, the weather station 
and accompanying facilities are the only estab- 
lishments now active on the island. But re- 
mains of ruined buildings constructed by both 
Japanese and American military forces during 
or after World War II are scattered everywhere. 
The earth consists exclusively of coral sand and 
pebbles. The latter vary in dimensions from 
mere large sand grains to pieces of gravel more 
than 5 cm. in length (Fig. 10). Accumulation 
of humus was observed only in the E. triangle, 
where the vegetation was relatively well de- 
veloped. 
In summary, Marcus is extremely poor in land 
area, soil texture, and topographical diversities. 
How such a poverty reflects on the land biota 
will be described subsequently. It must be men- 
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