桜島転石海岸の潮間帯における貝類群集と転石の特性の関連

抄録

Intertidal molluscan communities were surveyed on six lava boulder shores on Sakurajima Island, Kagoshima Prefecture, which has a large active volcano. Each shore was thought to have different geological characteristics since they consist of lava extruded during four volcanic eruptions (A.D.1471-76, 1779, 1914, 1946). This study aims to show the relationship between the community structure of intertidal Mollusca and the characteristics of boulders on the shore as well as to compare the intertidal molluscan fauna of shores formed by different eruptions on Sakurajima Island. The survey was carried out between May and July 2001. The number of each species and the size of boulders in quadrats placed at regular intervals were recorded. Thirty species were found on the six shores and the density of all species showed more than ten-fold differences in the middle intertidal area between the shores with the highest and the lowest densities. Cluster analysis did not group molluscan communities in the shores with lava extruded during the same eruption because of variation within each shore. The result of multiple regression analysis showed that number of species increased with decreasing tidal level and increasing surface area of boulders per quadrat, and that the number of molluscan individuals increased with the mean volume of boulders.