Two species of Amphipoda (Hyperiidae), Themisto libellula (Mandt, 1822) and Themisto abyssorum (Boeck, 1870), were collected with the use of a WP-2 net from the area between Nordkapp and Spitsbergen (73° to 78° N) in July of 1993,1996,1997 and 1998. Densities ranged from 6 to 992 ind. 100 m-3 (T. abyssorum) and from 8 to 448 ind. 100 m-3 (r. libellula) and respective total biomass of T. abyssorum from 65.6 to 81.2 mg d.w. 100 m-3 and T. libellula from 59.9 to 131.5 mg d.w. 100 m-3.
Non-crustacean plankton was studied during summer cruises to the northern Norwegian Sea from 1996 to 1998. The dominant species in the investigated area were Aglantha digitale (Hydrozoa) and Sagitta elegans (Chaetognatha). The average density, mean biomass and interannual changes of zooplankton are presented against the background of sea temperatures. The results of this work indicate the very strong inter-annual variability of non-crustacean zooplankton abundance. Correlations with minor changes in sea temperature were noted only for hydromedusae.