| Summary: | The distribution of the arctic calanoid copepod Pseudocalanus acuspes was examined during the summer (August) of 1990, and the spring (May) of 1991 in the waters of Barrow Strait and Resolute Passage, N.W.T. Water column particulates (chlorophyll a, phaeopigments, silicates, and CHN) were also concurrently described. Copepod incubations (ammonia/urea production and oxygen consumption translated to O:N ratios) and distribution information were used to describe aspects of the nutrition of P. acuspes. A strong diel migration by P. acuspes, moving to the near underice surface at night, was detected during the month of May. During August, the bulk of the summer population remains near the sinking chlorophyll maximum (depths of 15-50m). Tidal current erosion and mixing are likely to be important in making epontic algae available for P. acuspes. Low O:N ratios (by atoms) measured during the summer and late spring (8.19-11.94) indicate high grazing rates on phytoplankton and probably an associated production of lipids. The O:N ratios are the lowest reported for arctic copepods. Feeding selection experiments were conducted using the natural summer phytoplankton assemblage from Resolute Passage, N.W.T., in August, 1991. P. acuspes tended to positively select the diatoms Nitzschia seriata, a species of Thalassiosira, and one species of Navicula. It avoided a species of Fragilaria. The strength of the feeding selection was shown to be dependant on the extent of feeding (depletion of chlorophyll), and could be explained by selection for the largest "effective food parcel size". Feeding selection by P. acuspes is an important aspect of its natural feeding ecology.
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