Life history and utilization of the beach face slope by the sandy beach isopod Excirolana chiltoni in Sendai Bay, northern Japan

Abstract

The life history of a cirolanid isopod, Excirolana chiltoni Richardson, 1905, was studied on a sandy beach in Sendai Bay, northern Japan, during the period October 1996 to March 1998. Cohort analyses indicated two or three age groups in each sample with a life span estimated at 2 years. The growth rate was high in the warm season and low in winter. The breeding season lasted from early April through to late September. Two-year-old females began to carry embryos earlier, followed by the smaller 1-year-olds. Excirolana chiltoni showed spatial segregation during the breeding season. Namely, ovigerous females occurred on the high shore and juveniles were closest to sea. Thus, E. chiltoni utilize environmental gradients along the beach face slope on sandy beaches throughout their life history.