138 
survey line varied from 10 to 20, according to 
the inclination of the bottom; 197 sets of 
quadrat data were obtained. All data needed for 
analysis were recorded on hand-sort edge- 
punched cards to facilitate the compilation of 
the data. Readings of depth were adjusted to the 
low watermark of spring tide, and the quadrat 
of 0 m level indicates the quadrats placed above 
the low watermark. The depth represented as 1 
m concerns the quadrat level laid down between 
low watermark and 1 m deep, and so on. 
RESULTS 
Stratal Structure of Sargassum Community 
Twelve species of Sargassum, one species of 
Cystophyllum, and one species of Hizikia oc- 
curred in the quadrats surveyed (Table 1). The 
fruiting period of these species is revealed by 
analysing the data obtained from surveys of 
the floating seaweeds (Segawa, Sawada, Higaki, 
and Yoshida, 1939) . According to these results 
and our observations made at the stations in- 
vestigated, all of the species growing there ex- 
cept Sargassum ringgoldianum had passed their 
fruiting period. Most of the individuals of each 
perennial species had lost their long branches 
bearing the receptacles, and most of the branches 
of the next year class had reached a length of 
30-40 cm. Therefore, the vegetation was at its 
lowest height for the year. However, S . ring- 
goldianum was taller than the rest. Annual 
TABLE 1 
Species of Sargassum and Related Genera 
Observed in Quadrats 
S. thunbergii (Mertens) O. Kuntze 
S, nigrifolium Yendo 
S. hemiphyllum C. Agardh 
S. confusum Agardh 
S. micracanthum (Kiitzing) Yendo 
S. ringgoldianum Harvey 
S, fulvellum Agardh 
S' patens C. Agardh 
S. tortile C. Agardh 
S. yendoi Okamura et Yamada ? 
S. piluliferum C. Agardh 
S' serratifolium J. Agardh 
Cystophyllum sisymbrioides J. Agardh 
Myagropsis my agr aides (Turner) Fensholt) 
Hizikia fusiforme (Harvey) Okamura 
PACIFIC SCIENCE, Vol. XVII, April 1963 
species such as S. horneri were in a very early 
stage of growth. At the time of the year when 
the survey was done, therefore, all species of 
Sargassum were considered to contribute to- the 
same layer, and cover degree of the species was 
rather easy to determine. Stratal difference may 
be developed among the species of Sargassum 
during the period from winter to spring, be- 
cause of the difference in the growing and fruit- 
ing periods of the species concerned (cf Se- 
gawa, Sawada, Higaki, and Yoshida, I960). 
Species other than Sargassum occurred mainly 
at shallower places, and there was almost the 
total lack of a frondose lower layer under the 
well-developed layer of Sargassum . The crustose 
layer was represented by species of unarticu- 
lated corallines. In the area where the upper 
layer was open because of the absence of Sargas- 
sum, several species of frondose algae other 
than Sargassum formed a lower layer. Although 
the population of Sargassum became sparse in 
deeper places, the society of the lower frondose 
strata was not developed. This fact may be at- 
tributed partly to the survey time, when many 
kinds of algae were extremely depauperate in 
growth for the year. 
Vertical Distribution of Species 
The substratum profile and the vertical distri- 
bution of some of the major species of Sargas- 
sum are presented ( Fig. 5 ) for each station. 
At station l(Fig. 5), the rocky bottom is 
evenly sloped to a depth of more than 8 m, 
then it gives way to- sand. The dominant species 
of Sargassum changes with increasing depth: 
5'. piluliferum is predominant at depths less 
than 3 m, then S. patens predominates over the 
other species on rock surfaces about 3 m deep, 
and finally S. serratifolium predominates in 
deeper places. On the other hand, at station 6 
(Fig. 5), the bottom is of boulders for the most 
part and there is some solid rock bottom in 
places. The slope of the bottom is lower than 
at station 1. While three of the species of Sar- 
gassum just mentioned are also present here, 
their degree of cover and vertical range do not 
coincide with what was found at station 1. As 
stated above, the vertical ranges of the species 
are not the same among the stations surveyed. 
An explanation for these differences is desirable. 
