Breeding season and early developmental stage of a urchin, Sterechinus neumayeri (Meissner), at Syowa Station, Antarctica

Abstract

The breeding season and early developmental stage of a sea urchin, Sterechinus neumayeri, which is widely distributed in Antarctic coastal waters, were studied. A year-round sampling of the urchin was carried out at Syowa Station during the 40th Japanese Antarctic Research Expedition (JARE-40) over-wintering period (February 1999-February 2000) using bait traps. The urchin entered into traps in both the autumn to mid-winter and late spring to summer periods, but not from late winter to early spring. According to the observed facts, that all individuals caught before mid-winter had mature sexual organs and that more than half of the collected urchins during late spring were post-spawning individuals, natural spawning seemed to occur from late winter to spring at the study site. In nearly freezing seawater, spawning and fertilization were experimentally induced using samples collected both in late autumn and late spring. The early development of the embryo was successfully observed for a month using the latter samples. The first cleavage occurred within 20 hours after insemination, and the successive development of the embryo reached the morula and blastula stages for 2 and 3 days, respectively. The embryo grew slowly and finally developed to a prism larva via the gastrula stage within 18 days after fertilization.