Red tide occurrences in the coastal zone increased dramatically with the spread of eutrophication during the period of high economic growth. The discovery that seaweed beds and seagrass Zostera beds enormous amounts of algicidal bacteria indicates that the land-reclamation and vertical shore protection projects carried out in this period, which reduced the seaweed beds and seagrass beds, also eliminated their red tide deterrence capability. The creation and restoration of seaweed beds and seagrass beds in shallow water ecosystems, and tidal flats should be effective as a red tide prevention strategies.