Abstract Quantity and composition of zooplankton at three stations in Isafjord-deep, northwest Iceland, were studied from February 1987 to February 1988. Sampling was made with 335 Im mesh Bongo-net at approximately monthly intervals along with hydrographic measurements and measurements of chlorophyll a concentrations. Spring warming of the water began in early May and maximum temperatures (8–10° C) were observed during JulySeptember. The phytoplankton bloom started in early April, maximum chlorophyll a levels were observed in late April to the middle of May (c. 8 mg Chl a/m3 ), and a smaller ‘autumn increase’ was again observed in July to August kc. 3 mg Chl a/m3 ). The total zooplankton volume was highest in August (c. 32 m1l100 m ) while it was lowest in February 1987 > 1 ml/m3 ). During the winter months euphausiids dominated in terms of volume (> 90 %) while during the summer months the combined volume of fish larvae and 'other zooplankton' (mainly copepods and cirripedes) was similar to that of the ...