Ecological studies of Sargassum hemiphylum C. AGARDH in Obama Bay, Japan Sea.

Abstract

Sargassum hemiphyllum C. AGARDH was studied ecologically on the basis of materials collected at Hansti, Obama Bay, a branch bay of Wakasa Bay, in middle Honshu, facing the Japan Sea, from June 1980 to August 1981. Annually, laterals 1.40(±036) to 4.32 (±0.92) in number on their stem of which 0.70 (±0.63) to 2.66 (±1.03) are dropped off af ?? er becoming mature in June. After dying back, the basal part of primary laterals pwrsists on their stem as scars or remains. It was roughly estimated from the numberof scars that the longevity of the stenm or plant is 2-3 (-4) years. Lateral branches arise spirally on their primary lateral with a divergince of 1/3. Soon after fertile primary laterals degenerate in June, fresh primary laterals which are less than 10 or 20cm in lengh, begin to elongate and continue to grow, reaching a maximum length in April of the following year. In April, the first primary laterals attained a heighe of 69.0cm on an average. In May, the whole plant reached amaximum weight of 6.3g (wet weight) fo which 4.8g was from the first primary lateral, corresponding to 76.1%of the plant. On a primary lateral of up to 30cm in length, a total length of all lateral branches was about two timses longer than the length of their primary lateral. That of all lateral branches arising on primary lateral which grew to 50-80cm in length was 5-8 times longer. The species was dioevious: The ratio of female to male plants was 1:1. The primary laterals arising on the same stenm were of fhe same sex.