Sargassum at Tsuyazaki — Yoshida, Saw ADA, and HiGAKi 
141 
Objective Classification of Sargassum Commu- 
nity 
Goodall ( 1953 ) proposed a method of divid- 
ing vegetation samples into statistically homo- 
geneous groups. This method involves prepar- 
ing a 2 X 2 table whereon the correlation be- 
tween every pair of species is analysed by com- 
puting a value from the number of quadrats in 
which one or both of two particular species are 
present or not. An objective classification can 
be arrived at when, with respect to all species 
growing in the sample quadrats, no interspecific 
correlations of significant level occur within 
each group of quadrats, so that the quadrats 
may be divided into some homogeneous groups. 
The significance of interspecific correlation is 
decided by x 2 test, preparing the 2X2 table, 
as shown below: 
SPECIES B 
present 
absent 
Species A 
present 
absent 
a 
b 
C 
d 
a + c 
b + d 
a + b 
C+d 
n=a+b+c+d 
(ad-bc±n/2) 2 n 
(a+b) (c+d) (a+c) (b+d) 
Values of x 2 are calculated between every pair 
of the six species of Sargassum contained fre- 
quently in quadrats, and are shown in Table 2. 
Only two combinations, i.e., the pairs of S. ring- 
goldianum-S. piluliferum and S. tortile-S. pa- 
tens, have significant correlation at the 5% 
level. According to the first procedure of classi- 
fication proposed by Goodall (1953: 46-50), 
as a result of the elimination of quadrats con- 
taining one species of high frequency in those 
four species mentioned above, no species was 
found which has a significant interspecific cor- 
relation with the others in the final two groups 
obtained. However, the two groups obtained 
from this procedure are not useful because quad- 
rats belonging to one group are considerably 
intermixed with the others. 
Distribution of Algae Other than Sargassum 
Although attention was not centered on the 
distribution of algae other than Sargassum, ob- 
servational data on those algae were recorded 
as often as possible. The species observed in 
this survey are listed in Figure 9. The frequency 
of quadrats containing algae other than Sargas- 
sum is calculated for each depth, and the graph 
in Figure 10 is the result. This graph illustrates 
that the species other than Sargassum occurred 
in all quadrats laid above the low watermark, 
but that the frequency of their occurrence in 
quadrats decreases sharply with increasing 
depth. The range of the species growing at dif- 
ferent depths is shown in Figure 9. Dictyopteris 
undulata was observed in the deepest quadrat. 
The marine vegetation was richest in number 
of species at the place exposed to the strongest 
wave action, and more abundant in number of 
individuals near the low watermark. At deeper 
places the density of algae is less and the vege- 
tational cover may be provided by the species 
of Sargassum alone. 
DISCUSSION 
With respect to the stratal structure of the 
marine algal community, Segawa considered that 
three layers are recognized, i.e., the upper, lower, 
and crustose layers, when a well-developed vege- 
tation is being considered (Katada, 1958). The 
upper layer is more than 10 cm in height, and 
the crustose layer is composed of algae less 
than 1 cm high. At the time of the year when 
TABLE 2 
x 2 — Values between Six Species of Sargassum Frequently Encountered 
S. hemiphyllum 
S. piluliferum 
S. ringgoldianum 
S. tortile 
S. patens 
S. serratifolium 
6.093 
2.652 
4.330 
2.923 
1.661 
S. patens 
0.517 
7.337 
6.391 
8.405 
S. tortile 
2.527 
0.045 
0.000 
S. ringgoldianum 
2.197 
9-776 
S. piluliferum 
3.772 
