In ocean areas where the shortage of spores was a factor limiting growth, large quantities of one-year old brown macroalgae (Ecklonia cava) cultivated on artificial substrates were transplanted in large quantities to submerged breakwater to form beds. In November 1994 and January 1996, approximately 12,000 and 15,000 brown algae samples were transplanted to the site. After six years in March 2001, the area of the beds reached its maximum area of 8,000m^2, implying that the beds expanded at a rate of 20〜48m/year. In low temperature years, the attachment of large numbers of juvenile brown algae was the trigger for bed expansion. During the years when the beds were expanding (1994-2001) there was little feeding pressure from herbivorous animals. Although the submerged breakwaters along the Seisho Coast were originally intended as wave suppression features, they were very effective for creating seaweed beds and for protecting and nurturing marine organisms. In fact, it has been suggested that these breakwaters contributed to an increase in coastal fishery production. Unanticipated factors that contributed to limiting the growth of the beds included strong waves (Autumn 2001), which washed away sections of the brown algae beds, and also heavy grazing by herbivorous fish (Siganus fuscescens) (Autumn 2004). The localized algae beds that escaped grazing occurred in areas where the waves and currents created habitats with complex flow conditions. In addition, access to these areas was limited and they were characterized as having strong circular flow and near shore currents. While grazing by S. fuscescens resulted in the loss of approximately 80% of the brown algae beds, there has been considerable recovery of the brown algae beds since 2006. Long-term monitoring will be continued in the future to increase our understanding of the factors responsible for changes in the distribution patterns of brown algae beds established on submerged breakwaters.