Productivity of a Sargassum macrocarpum (Fucales, Phaeophyta) population in Fukawa Bay, Sea of Japan

The productive structure and productivity of a Sargassum macrocarpum C. Aga rdh population were studied from June 1993 to July 1994 in Fukawa Bay facin g the Sea of Japan, Yamaguchi Prefecture. S. macrocarpum formed a dense pop ulation at a depth of 8 m in the study area. Using the stratified clip tech nique, monthly changes in the productive structure from 1993 to 1994 were c larified. The dry weight of leaves and main branches increased with the elo ngation of branches. Thalli in the middle to high stratum began to bear rec eptacles from March 1994 and the dry weight of receptacles was approximatel y one-third of the standing crop in June. The loss of leaves increased from April to June 1994, and the loss of main branches and receptacles from Jun e to July 1994. Productivity of branches and receptacles reached maxima of 4.67 g dry wt/m(2) per day from February to March and 5.33 g dry wt/m(2) pe r day from April to May, respectively. Productivity of the leaves, however, was almost constant at approximately 2 g dry wt/m(2) per day from July 199 3 to March 1994. Therefore, maximum productivity of the S. macrocarpum popu lation of 7.17 g dry wt/m(2) per day occurred from February to March. Annua l net production of newly sprouting branches in June 1993 was 1600.1 g dry wt/m(2) per year based on the summation method, which was calculated from t he monthly changes in the productive structure.