First report on the annual reproductive cycle of Burchardi's cockle, Acrosterigma (=Vasticardium) burchardi Dunker 1877 (Bivalvia: Cardiidae) on a subtidal sand flat off southern Jeju Island, Korea

Abstract

We report for the first time on the annual gametogenesis of the Burchardi's cockle, Acrosterigma (=Vasticardium) burchardi (Dunker, 1877) on a subtidal sand flat off southern Jeju Island, Korea. Seasonal changes in gamete development and oocyte size were investigated using histology. Intermingled ovaries and testis in the gonads located in the foot indicated that, like other cockles, A. burchardi is a functional hermaphrodite. In August, early developing oocytes and spermatogonia were observed in gonads suggesting that gametogenesis commenced when the water temperature reached 22.7–28.5EC. Early vitellogenic oocytes 8–10 μm in diameter appeared in gonads from September to November when water temperatures ranged from 16.9 to 22.2°C. Oocyte size increased exponentially from November (8 μm) to April (53 μm). Condition index dropped dramatically from May (0.51) to June (0.38), indicating that the Burchardi's cockles off southern Jeju Island spawned during this period. A. burchardi spawning appeared to be synchronous, with the release of oocytes and sperm being observed only in May and June (16.4–22.8°C). The annual reproductive cycle of A. burchardi in Jeju Island could be summarized as (1) resting and early gametogenesis from August to January, (2) late gametogenesis from February to April, (3) ripe from March to May, (4) spawning in May and June, and (5) spent/resorbing in July and August.