216 
Fig. 1. Adult manini, Acanthurus triostegus sand- 
vicensis, from Hawaii. Standard length, 154 mm. 
HABITAT 
In the Hawaiian Islands the manini occupies 
a diversity of habitats. It occurs in bays, harbors, 
and exposed reef areas. It abounds in tide pools 
and shallow water, yet is known at depths of at 
least 100 ft. Areas of very turbid and brackish 
water are usually avoided, but a few manini have 
been collected even in these regions. 
Like most reef fishes, the manini avoids ex- 
tensive stretches of sand or mud bottom, pre- 
ferring instead the nearness of holes or crevices 
in the reef for shelter and solid bottom for the 
growth of its algal food. 
The manini appears to be more restricted in 
habitat in the Gilbert and Marshall islands, pos- 
sibly because of the sharper definition of the 
ecological zones of these atolls. It occurs in these 
atolls both in the lagoon and outer reef areas; 
however it seems to be confined to relatively 
shallow water. On the outer reef the fish were 
seen only on the reef flat, the young in great 
abundance in the shallower sections and the 
adults on the seaward portions (for data from 
a reef-flat transect in the Gilbert Islands, see 
Randall, 1955 h: 181). The species was only 
rarely observed in the turbulent surge channel 
zone and was never seen on the coralliferous 
terrace (benched area of living coral offshore 
from the reef flat). 
As in the Gilberts and Marshalls, the presence 
of heavy coralline areas in the Hawaiian Islands 
seems to limit the manini. This is apparent from 
the underwater transect work of Brock ( 1954). 
PACIFIC SCIENCE, Vol. XV, April 1961 
Areas like the northern part of Kealakekua Bay, 
Hawaii, where the coral growth is extremely rich 
for the Hawaiian region, are almost devoid of 
manini. Since this species is herbivorous, its dim- 
inution in coral areas may be associated with 
the small amount of substratum available for the 
growth of algae. Surprisingly, other surgeon- 
fishes such as Acanthurus leucopareius , A. achil- 
les , Zebrasoma flavescens , and Ctenochaetus 
strigosus , usually less abundant than manini, are 
the most common fishes in this part of the bay. 
With the exception of C. strigosus which is a 
detritus feeder (Randall, 1955^) , these species 
are more inclined to crop close to the substratum 
than the manini, judging from the greater 
amount of inorganic debris in their stomach 
contents, and they may therefore be superior 
competitors under such conditions. 
The eggs and larvae of the manini are pelagic. 
This has been ascertained by a study of develop- 
ment following artificial fertilization of the eggs, 
by the capture of larvae in plankton nets, and 
by the taking of the late postlarval or acronurus 
stage at night lights offshore. 
A total of 11 acanthurid larvae (at least 3 
of which are manini), 4.2-87 mm. in total 
length, were found in the plankton collections 
from Hawaiian waters of Cruises 4 (May 1950) 
and 6 (August 1950) of the "Hugh M. Smith,” 
a POFI research vessel. These fish were taken 
at eight stations ranging from about 10 to 140 
mi. from the nearest island (for more exact 
locations, see King and Hida, 1954: fig. 1, sta- 
tions 1A, 10, 13, 15, 17, and 23 of Cruise 4 
and stations 7 and 14 of Cruise 6). They were 
captured in horizontal tows made with fine- 
meshed plankton nets (1 m.) which sampled 
three different levels simultaneously. For both 
cruises combined, a total of 58 hauls were made 
at the surface, 24 at a depth of 50 m., and 112 
at depths from 100 to 300 m. Six of the larvae 
were taken at the surface, 5 at 50 m., and none 
at greater depths. The failure to find more larvae 
in these collections is probably due to the dis- 
tance from land of most of the stations. Only 6 
of the 29 stations of each cruise were within 25 
mi. of any of the Hawaiian Islands and only 1 
within 10 mi. The absence of larval Acanthurus 
longer than 8.7 mm. in the collections is prob- 
ably due to the ability of larger larvae to elude 
