Small-scale ontogenetic and diel vertical distributions of neritic copepods in Maizuru Bay, Japan

Abstract

Ontogenetic and diel vertical distributions of the dominant copepods Oithona davisae, Acartia spp. (A. hudsonica and A. omorii) and Paracalanus crassirostris were studied in Maizuru Bay, middle Japan. A consistent ontogenetic pattern was found during daytime for all the species: mean distribution depths moved upwards with later naupliar stages and downwards during copepodite development. Details of this pattern vary with the species. Vertical distribution of P. crassirostris eggs is similar to that of the 1st naupliar stage (N1), while in Acartia egg distribution depends on adult females; Acartia Nl is always concentrated in water close to the bottom independent of egg distribution. This indicates that P. crassirostris eggs may drift until hatching while most Acartia eggs sink to the bottom before hatching. The ontogenetic distributional pattern observed in the daytime is generally obscured at night due to stage-specific nocturnal migrations.