溶岩質転石海岸における二枚貝 3 種の分布の季節変動

抄録

Seasonal changes in size and density of the three bivalve species, Acropsis (Galactella) symmetrica (Reeve, 1844), Barbatina (Abarbatia) lima (Reeve, 1844) and Cardita leana Dunker, 1860 were studied in the intertidal area on a lava seashore in southwestern Japan. These three species are distributed sympatrically on a boulder shore on Sakurajima Island (31°35′N, 130°36′E) in Kagoshima Prefecture, Kyushu, Japan. Juveniles (<3 mm shell length) of A. symmetrica were frequently observed from September to December. A. symmetrica seems to be an annually-reproducing species. In B. lima, juveniles were observed from August to March. Juveniles of C. leana were observed in April and from October to December. Frequency distributions of shell size suggest lifespans for B. lima and C. leana to be more than one year. B. lima was found distributed widely from the lower to the middle zones, while the other two species were limited to the lower zone. It was estimated that most of the newly settled juveniles of B. lima died in the middle zone. The density of B. lima was greatest in the middle zone in June, and in the lower zone in November.