Changes in algal ‰ora by removing the sea urchin Diadema spp. were studied in Haidaura Bay, Mie Prefecture, central Japan in 1999Japan in , 2004Japan in and 2014. The algal ‰ora and distribution of seaweed beds and barren ground were surveyed by skin diving at 10 sampling sites. Thirteen species of Chlorophyceae, 30 species of Phaeophyceae and 67 species of Rhodophyceae were observed during the study period. In the mouth of the bay, seaweed beds were stable and the number of algal species did not show remarkable changes from 1999 to 2014.As a result of the recovery of seaweed beds from barren grounds by removing Diadema spp., the number of algal species drastically increased in the inner parts of the bay. Consequently, removing Diadema spp. increased the number of algal species including various small algae in Diadema-dominated barren grounds.

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