EŠects associated with removing the sea urchin Diadema spp. from an area of barren ground were examined in Haidaura Bay in Mie Prefecture, central Japan, from December 2009 to December 2012. Diadema spp. were harvested using scoop nets and spears from boats, or crushed by divers using metal rods. Three experimental areas in which initial Diadema spp. densities were high (8.

Seasonal changes in the contents of two photosynthates, namely, mannitol and laminaran, were investigated in Ecklonia cava Kjellman with reference to its maturation. The samples were collected from a depth of 8 m in Nishiki Bay, central Japan. The mannitol and laminaran contents in the bladelets were measured. We also determined the content of these photosynthates in the bladelets occupying different positions on the frond and in the sorus and non-sorus portions of the bladelets. The maturation of sori initiated in July and peaked in October. The content of the two photosynthates in the bladelets was low in winter; this coincided with the active formation of new bladelets. Mannitol levels were high during the beginning of the maturation season in summer. Laminaran, in particular, was present in the bladelets only in summer. The laminaran content was higher in the sorus portions than in the non-sorus ones; however, the mannitol content was almost equal in both portions. The laminaran content was high only in the bladelets just prior to maturation and in the mature bladelets at the beginning of the maturation season. These results suggested that mannitol and laminaran were important energy sources for the maturation of E. cava from summer to autumn, and laminaran in particular was closely associated with the maturation of reproductive structures.

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Fragments of Ecklonia cava Kjellman were cultured under controlled laboratory conditions of light irradiance, water temperature, and photoperiod. To clarify the relationship between the maturation of E. cava and the photosynthetic products, laminaran, the content in the fragments was measured with the progress of maturation. The culture conditions ranged from 12.5 to 100 mmol m -2 s -1 , 10-25°C, and 14 : 10 h LD (light : dark) to 10 : 14 h LD. In the case of low light conditions, despite an optimum temperature for maturation, the fragments did not form sori and laminaran was not accumulated during the culture period. In the case of sufficient light and non-optimum temperature conditions, the fragments did not form sori, but laminaran was accumulated. When the fragments were cultured under optimum light and temperature conditions for maturation, laminaran was accumulated in the early stage of maturation, just before or after cortex of the bladelets thickened, and decreased with the progress of maturation, and all fragments matured regardless of the length of the photoperiod. So, these results support the idea that laminaran is used as the main respiratory substrate in the maturation of E. cava.

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.