Ecological Studies of Sargassum miyabei YENDO in Maizuru Bay, Japan Sea

Abstract

Ecological studies of sargassum miyabei, which is an important species in forming Sargassum bed in shallow waters, were carried out at Nagahama, Maizuru Bay on the basis of plants collected monthly from August 1980 to July 1981. The stem, which is perennial, has primary laterals from 2.5 (±0.9) to 6.7 (±1.7) with various legths, of which 1.2 (±0.8) to 2.9 (±1.0) grew to more than 20cm in length, attained their maximum length and weight in July 1981, matured with receptacles, and finally died back. Primary laterals continued to grow from August 1980 to July 1981, with two rapid growing periods from November to January and April to June. The first primary lateral weighted on an average 17.5g in June and 30.2g in July, which corresponded to 95.8 and 82.0% of the total weight of the palnt, respectively. When primary laterals grew to 30cm or a little longer, they produced lateral branches. The arrangement in length of lateral branches on the primary lateral was fusiform or pyramidal in vertical view. However, when the apex of the primary lateral was damaged or cut off, its lateral branches elongated abnormally. The longevity of stem was estimated by counting the scars or basal remains on the stem of shed primary laterals. The species is dioecious and the plant with several primary laterals is of the same sex.