Ecological Studies of Sargassum horneri (TURNER) C. AGARDH in Obama Bay, Japan Sea

Abstract

Sargassum horneri which grows in Obama Bay, a branch bay of wakasa Bay facing the Japan Sea, was studied ecologically. Ten plants were collected monthly on the sheltered roky shore from October 1980 to may 1981 and on the exposed rocky shore from August 1981 to May 1982. On the sheltered shore, the primary laterals reached an average of 161.0cm in May, whereas on the exposed shore their maximum length was 99.0cm in May. In the former a daily growth in length of the primary laterals was 1.96cm from December to January, whereas that in the latter was 0.96cm from December to January. The average weight of the plants from the sheltered shore was 34.0g (dry weight) in May, corresponding to 0.21g per centimeter of the primary lateral. Those from the exposed shore were 21.5g (d. w.), which was equivalent to 0.23g per centimeter of the primary lateral. When the plants from the exposed shore grew over 90cm in length, their weight increased abruptly, adding 16g with an elongation of 10cm of the primary lateral, while plants over 120cm in length from the sheltered shore increased in weight by only 7.0g with an elongation of 10cm of the primary lateral. The leaves of the young plant and the lateral branches of the primary lateral were produced spirally with a divergence of 2/5, and this pattern did not change for the entire length of the primary lateral.