| 研究実績の概要 |
In Mushima Island, Ojika-machi, Nagasaki Prefecture, two study sites were selected in 2017 October. In 2018 September, 6 permanent stations were setup, two in site A and 4 in site B. At site A, one station was fertilized with inorganic P and the other was not fertilized. Both remained unprotected from herbivores. At site B, the stations were stup as 2x2 matrix of inorganic P fertilization and herbivore protection. Concrete blocks with Sargassum embryos were placed at each site. The survival rate of these embryos were monitored monthly at each site. By 2018 December, there was no evidence of any embryos surviving at each site. The reason for the poor survival rates are not clear, but we believe that water temperature is the cause, since the water temperature did not drop below 14 degrees C during the winter and were as high as 28 degrees C during the summer. Sargassum embryos have better survival rates in cooler waters.
At the same time, interactions between seaweed and sea urchins are being examined at our field station. It is clear that when dead sea urchins are present, grazing activity of live sea urchins are reduced. This suggests that sea urchins change their behavior during stress, which can reduce grazing.
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