Sargassum at Tsuyazaki — Yoshida, Saw ADA, and Higaki 
139 
Fig. 5. Profile of substratum and distribution of species: ri, S. ringgoldianum; pi, S. piluliferum; to, 
S. tortile; fu, S. julvellum; pa, S. patens; se, S. serrati folium. 
Vegetational Cover 
The percentage of vegetational cover was ap- 
proximated by eye for several square meters 
around the spot where the frame of the quadrat 
was laid down. For this measurement, crustose 
algae were not included. As shown in a later 
section, algae other than Sargassum were found 
mostly in the relatively shallow places and had 
only a slight effect on the degree of vegetational 
cover in the deeper places. 
Variation in average vegetational cover with 
increasing depth was determined using the 
whole quadrat samples. This mean value is in- 
dicated with a dotted line in Figure 6. From this 
figure it can be seen that the average vegeta- 
tional cover is nearly uniform from the low 
watermark to 5 m deep, and then decreases 
gradually in places beyond the 5 m depth. Here 
only depth of water is taken into consideration 
as an environmental factor. 
In this study, the 13 stations surveyed are 
placed in three groups according to the strength 
of wave action. For each of the three groups, 
then, the relationship between the depth of 
water and average vegetational cover is plotted 
in Figure 6 by the three solid lines. At the 
rather sheltered stations subject to weak wave 
action, the maximum value for average vegeta- 
tional cover is found at the 1 m depth. As 
deeper water is reached the values fall quickly. 
For the areas where wave action is moderate, 
vegetational cover reaches its maximum 2-3 m 
below low watermark and gradually decreases 
with increasing depth. An examination of the 
values from the stations exposed to the strong- 
est wave action shows the values for average 
vegetational cover reach 100% above the low 
watermark, then fall and again come to a peak 
at the depth of 4-6 m. Algae other than Sargas- 
sum contribute to the vegetational cover in shal- 
lower places exposed to strong wave action. 
Therefore, when the degree of cover for Sargas- 
sum only is considered, the depth at which the 
maximum value for vegetational cover is found 
becomes deeper with increasing strength of 
wave action. 
