Reproductive biology of the land crab Epigrapsus politus Heller, 1862 (Brachyura: Gecarcinidae) on Iriomote-jima, Japan

Abstract

Abstract The breeding cycle of the land crab Epigrapsus politusHeller, 1862 (Gecarcinidae) was studied through a mark-recapture experiment on subtropical Iriomote-jima, Japan between September and November 2017. The abundance of E. politus at the cobble shore increased during the breeding season, and then decreased. Crab density was estimated to be 423.5 over 20 m2. The population showed a bimodal and a monomodal body-length frequency for males and females, respectively. Lifespan was estimated to be between one and two or three years. Ovigerous (egg bearing) females were detected from early September to late November, with the highest abundance occurring between late September and early November. The proportion of embryonic development (non-eyed and eyed eggs) of ovigerous females and the presence or absence of embryos and embryonic development of recaptured females showed that larvae were released on the days after the full moon. In comparison, egg extrusion occurred during the period of the previous full moon, i.e., eggs were incubated for four weeks. Females produced one brood within a single breeding season. The breeding ecology of E. politus was characterized as being short and occurring in a cooler season than that of other gecarcinids inhabiting the subtropical islands of the northwest Pacific.