Abundance, vertical distribution and life cycle patterns of the hydromedusa Aglantha digitale in the Oyashio region, western subarctic Pacific

Abstract

Analyses of monthly depth-stratified (0–2000 m) sampling data in the Oyashio region have revealed that Aglantha digitale is distributed largely in the upper 250 m throughout the year. Population biomass ranged from <30 mg DW m⁻² (January) to 1575 mg DW m⁻² (August), with an annual mean of 186 mg DW m⁻². Judging from seasonal sequences of the population structure, the generation length of A. digitale is considered to be one year with their spawning season in June-September, which is consistent with that observed at Station P in the eastern subarctic Pacific.