Stage-specific habitats of Calanus finmarchicus and Calanus helgolandicus in a stratified northern Norwegian fjord

During 12 months from April 1997, Calanus spp, copepodites were sampled in the 380-m deep Saltfjord by means of a 200-mum WP-2 net at four depth inter vals. Nauplii were sampled with a 100-mum bongo net. Chlorophyll a and phyt oplankton were sampled with a hose in the 0-40 m depth range. Environmental variables were recorded by CTD and an in situ fluorimeter. C. helgolandicu s occurred in low numbers as adults and CV during most of the year. During the spring bloom in April, it avoided the upper cold 0-50 m depth range, wh ere C. finmarchicus reproduced. In August-September, adults of the two spec ies were equally numerous in the 0-50 m depth range. The adult C. finmarchi cus had probably developed from the local spring generation, whereas C. hel golandicus had probably been imported from shelf waters. Nauplii present in August may be attributed to both species, but they did not grow into CI lo cally. Therefore, C. finmarchicus CV that accumulated in September-October were more likely imported from the shelf, probably by surface advection. Pr edators possibly reduced numbers up to January 1998, when both species agai n increased, probably because of deep inflow of shelf water. (C) 2000 Inter national Council for the Exploration of the Sea.