Sources of urea in arctic seas:zooplankton metabolism

The copepod Pseudocalanus acuspes in the high a r c t ~c 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 ammonla 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 Metr~dia longa, similarly demonstrated high levels of urea excretlon The Calanus spp. showed strong correlation between slze (dry welght) and metabolic rates for oxygen consumption and for ammonia excretlon, and, for C. glacialls, 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 striklng changes in weight-spec~fic metabolism with season. For all species examined, weightspeclfic estimates of respiration and excretion frequently yielded 0 . N ratios less than 20, and occasionally less than 10, when urea and ammonia excretion were c o m b ~n e d in the calculations.