DIEL CHANGES IN THE CARBON AND NITROGEN-CONTENT OF THE COPEPOD METRIDIA-LUCENS

Diel changes in the near-surface (0-50 m) abundance, prosome length, a nd carbon and nitrogen content of the copepod Metridia lucens were mea sured in Deep Cove, Doubtful Sound, New Zealand (45 degrees 27'S, 167 degrees 9'E) between 3 and 6 September 1996. Metridia lucens showed ma ximal abundance at night, suggesting a pattern of normal diel vertical migration (DVM). The change in abundance suggested that the descent o f the population occurred similar to 1 h prior to dawn and the ascent similar to 1 h after dusk. However, a proportion of the population rem ained near the surface during the day. Although there was no diel patt ern in the prosome length of M. lucens collected near the surface, the re was a marked diel cycle in the measured carbon and nitrogen content s, with maximal values being measured towards the end of the night pri or to the downward migration. We suggest that this diel cycle in the m easured elemental content was caused by DVM occurring more strongly in those animals which had a better body condition, i.e. a higher elemen tal content per unit length.