Relationships between Wave Forces and Distribution Patterns of the Sea Urchin Strongylocentrotus nudus on the Coastal Artificial Structures.

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The effects of wave forces on the distribution patterns of the sea urchin <I>Strongylocentrotus nudus</I> were studied in a coastal area where a power plant sited at the western part of Shakotan, Hokkaido. To estimate the wave effects at different stations set along breakwaters and on rocky beds, hemispherical plaster blocks were set at depths of 2 m, 4 m, 6 m and 8 m at each station and the rate of plaster weight loss due to wave action was measured. Density of sea urchin and coverage of seaweeds were investigated at the same time on vertical and bottom surfaces of each station. Density of sea urchin on each station fluctuated corresponding to seasonal changes of wave condition. On exposed side of the northern breakwater, where the wave condition was the hardest and the coverage of seaweeds was relatively high, the sea urchin densities on the upper part of vertical surface (the depth were ranged from 0 to 5 m) were low. They became extremely low on every vertical surface, especially in stormy season from fall to winter. On sheltered side of the breakwaters under relatively calm conditions, seaweeds covered only shallow parts where sea urchins swarmed throughout seasons.
日本水産増殖学会の論文