Sargassum at Tsuyazaki — Yoshida, Saw ADA, and Higaki 
143 
lation in relation to the gradient of environ- 
mental factors, rather than centering it on classi- 
fying the communities. 
The junior author has reported that the verti- 
cal distribution of a species of Sargassum is 
hardly explained when only the depth of water 
is taken into consideration, and that, in addi- 
tion, presence or absence of a species at a certain 
station may partly be determined by the degree 
of exposure to wave action (Yoshida, 1961). 
At present, our knowledge is insufficient to 
elucidate the detailed effect of many environ- 
mental factors on the distribution of the species. 
For marine plants, increasing the depth of water 
has an important effect on growth in connection 
with the diminishing intensity and variation in 
the spectrum of the light penetrating into the 
water. On the other hand, we must take into 
account the other environmental factors, such 
as wave action or the turbulence of water. 
There is also a resultant complex of several 
factors. According to Gessner ( 1955: 198-209), 
the movement of water may have a close re- 
lationship with the assimilation and respiration 
rates of marine algae. It has already been re- 
(Codium fragile) 
Dictyota dichotoma 
Dictyopteris undulata 
Pachydictyon coriaceum 
Padina crassa 
P. japonlca 
P. arborescens 
Zonaria rtiesingiana 
Stypopodium zonale 
Undaria pinnatifida 
Eisenia bicyclis 
(Ecklonia kurome) 
Pterocladia tenuis 
Chondrococcus hornemanni 
Jania sp. 
Amphiroa ephedra ea 
A. erassi ssirna 
A. dilatata 
Cora Hina pilullfera 
Lithophyllum okamural 
Laureneia okamurai 
L. undulata 
(Plocamiua telfairiae) 
Fig. 9. Vertical ranges of distribution of algae other 
than Sargassum. Species in parenthesis did not occur 
in quadrats. 
% 
Fig. 10. Frequency in occurence of algae other than 
Sargassum (cf Fig. 9) in relation to water depth. 
ported that the distribution pattern of inter- 
tidal organisms is greatly affected by the turbu- 
lence of water (Southward and Orton, 1954). 
In this present study the distribution pattern 
of the species of Sargassum is clearly shown by 
the two-dimensional gradient analysis improved 
by Whittaker (1956). Two principal environ- 
mental gradients considered here are (a) the 
depth of water, and (b) the exposure to wave 
action. In the area surveyed the tidal current 
is faster where the shore is exposed to the 
stronger wave action, as stated above. It is 
hardly possible to treat the two factors, namely, 
exposure to wave action and speed of tidal 
current, independently. 
Determining the lower limit of the marine 
vegetation was prevented by the diving ability 
of the observer. It is observed around Tsuzumi 
islet that the species of Sargassum grow at 
places deeper than 10 m, where hard bottoms 
are found. At most cf the stations, the hard 
bottom gives way to sand before what would 
seem to be the lower potential limit for Sargas- 
sum growth is reached. 
SUMMARY 
The Sargassum community found in the 
upper part of the subtidal region in the sea 
around Tsuyazaki, North Kyushu, Japan was 
studied phytosociologically in July and August, 
1959. It seems that this community can not be 
divided successfully into smaller groups by ap- 
plying Goodall’s objective method of using posi- 
tive interspecific correlation. The gradient analy- 
sis method developed by Whittaker (1956) 
