MEPS 179:41-54 (1999)  -  doi:10.3354/meps179041

Sources of urea in arctic seas: zooplankton metabolism

R. J. Conover1,2,*, K. R. Gustavson1,**

1Department of Biology, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada
2Department of Fisheries and Oceans, Biological Sciences Branch, Bedford Institute of Oceanography, PO Box 1006, Dartmouth, Nova Scotia B2Y 4A2, Canada
Present addresses:
*7415 McAllister Road, RR2, Bewdley, Ontario K0L 1E0, Canada. E-mail:
**Department of Geography, University of Victoria, PO Box 3050, Victoria, British Columbia V8W 3P5, Canada

ABSTRACT: The copepod Pseudocalanus acuspes in the high arctic frequently occurs under fast ice in April and May, where it apparently feeds on ice algae. Excretion measurements for this species in summer from Barrow Strait, Northwest Territories, Canada, showed that urea frequently exceeded ammonia as the primary nitrogenous excretory product. Subsequent experiments in different seasons, also including observations on several other species of arctic zooplankton, notably the copepods Calanus hyperboreus, C. glacialis and Metridia longa, similarly demonstrated high levels of urea excretion. The Calanus spp. showed strong correlation between size (dry weight) and metabolic rates for oxygen consumption and for ammonia excretion, and, for C. glacialis, between size and urea excretion as well. No size-related metabolic relationships were found for P. acuspes, probably because of the small size range of the experimental specimens used. However, P. acuspes and both Calanus species demonstrated striking changes in weight-specific metabolism with season. For all species examined, weight-specific estimates of respiration and excretion frequently yielded O:N ratios less than 20, and occasionally less than 10, when urea and ammonia excretion were combined in the calculations.

KEY WORDS: Urea · Ammonia · Nitrate · Total dissolved nitrogen · Zooplankton · Excretion · Respiration · O:N ratio · Arctic · Fast ice

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