Spatial variation in the annual reproductive cycle of Turbo (Batillus) cornutus (Gastropoda: Trochidae) at Jeju Island, Korea

Abstract

The annual reproductive cycle of the top shell Turbo cornutus from Jeju Island was investigated in two populations using histology. In the northern population, gametogenesis commenced in January as the surface water temperature reached 14 degrees C, while in the southern population gametogenesis began a month earlier, as the water temperature remained at 17 degrees C. Ripe top shells first appeared in June and spawning continued from June to October when water temperatures were between 20 and 24 degrees C. Histology indicated that the spawning period of the southern population was a month earlier and lasted longer (June-October) than in the northern population (July-September). The percentage gonad area of animals in the southern population in March and April was significantly higher than in the northern population (p < 0.05), suggesting that the gonads of the southern population matured earlier. The observed earlier maturation and the subsequent spawning of the top shells from the south coast of Jeju Island could be associated with the warmer water temperature and more favorable environmental conditions. The major spawning period of top shells observed in this study from July to September suggested that the currently implemented period of the fishing closure from June to August needs to be re-evaluated to protect more spawning adults in late summer.