Ecological studies of Sargassum ringgoldianum Harv. subsp. coreanum (J.Ag.) Yoshida in Obama Bay, Japan Sea. I. Growth of the stem in Sargassum ringgoldianum HARV. subsp. coreanum (J.AG.) YOSHIDA in Obama Bay, Japan Sea.

Abstract

The growth of length and weight of the stem and the relationship between the branching pattern of the stem and annual rings of the holdfast in Sargassum ringgoldianum HARV. subsp. coreanum (J. AG.) YOSHIDA (Sargassaceae, Phaeophyceae) growing in Obama Bay, a branch bay of Wakasa Bay located in the middle part of Honshu facing the Japan Sea were studied. The stem is dichoto-mously branched several times, thus the lowest axis and the dichotomies above the axis were named as stemsI, II, III, IV, and V in the order of branching from base to apex. Among the branches, stem I is the longest and heaviest and becomes longer and heavier with the age of the plant. The mean length and weight of stem I were 10.19cm (S. D. 4.09cm) and 1.54 g (S. D. 1.07g), respec-tively. Statistically, a total length of all branches of stem V plants measures 109.1 cm and its corresponding weight is 5.1g. Annual rings of the holdfast showed a direct relationship to the number of dichotomies. Stem I1 plants are one year old; stem I2 plants two years old; stem H plants three years old; and stem III plants four years old. This relationship was obscured in stem IV and stem V plants, because they were in various stages of growth and their ages varies from four to six years old. From these data it is shown that it is possible to determine the plant age of S. ringgoldianum from the branching of the stem without cutting the holdfast.