Occurrence pattern and reproductive ecology of the leucosiid crab Pyrhila pisum (De Haan) in tidal flats in Hakata Bay, Fukuoka, Japan

Abstract

Occurrence pattern and reproductive ecology of a leucosiid crab, Pyrhila pisum were surveyed in tidal flats in Hakata Bay, Fukuoka, northern Kyushu, Japan. Size composition of each sex (male, juvenile and adult females) including carcasses was analyzed, and developmental stages of embryos and combination of mating pairs were checked. A mark-recapture experiment on adult crabs was conducted. In the study site, P. pisum was observed during 5 months only (late April to mid September). Carcasses were rarely found, and many adult crabs probably survived and migrated to the deeper subtidal zone after September. Four cohorts were detected in both sexes, and adults did not molt during their reproduction. Reproduction started after May in two large-sized adult cohorts. Female adults could spawn eggs three times. Two juvenile female cohorts were detected in May, and they joined reproduction after most of them had attained maturity by a puberty molt in late June and late July. Adult females copulated regularly in their hard-shell condition, and mating was observed even for ovigerous females.