Synchronized spawning of abalone Haliotis diversicolor triggered by typhoon events in Sagami Bay, Japan

Abstract

To elucidate the external cues triggering spawning of Haliotis diversicolor, changes in the gonads of adults and the occurrence of newly settled post-larvae were monitored from 2001 to 2004 in Sagami Bay, Japan. The gonad index (GI) and gonad somatic index (GSI) of both sexes began to increase between April and June 2002, peaked in September, and then decreased signifi- cantly by early October. In other years, GI and GSI were significantly lower in autumn. Between June and September in each year, almost all females had a mature ovary and most were capable of spawn- ing, but the occurrence of newly settled post-larvae (< 500 µm in shell length) was strictly limited to the periods just after typhoons passed through the study area. The GI and GSI of both sexes also decreased significantly only after typhoon events. Although mature adults experienced various changes in seawater temperature, tidal height and lunar phase during the survey periods, evidence of spawning was observed only after typhoon events. There were no specific trends in seawater tem- perature and lunar phase before newly settled post-larvae were collected. Our results suggest that spawning of H. diversicolor is strongly associated with typhoon events. Most individuals had an immature ovary just after the passage of a typhoon. However, 1 mo after spawning, most individuals had a mature ovary with a high GI, suggesting that H. diversicolor requires an interval of about 1 mo between successive spawning events.