Oxygen consumption and ammonia and phosphate excretion in pond zooplankton

Abstract

Respiration and ammonia and phosphate excretion were studied in the temperature‐acclimated zooplankton of a small eutrophic fishpond. The zooplankton included species of Cyclopoida, Cladocera, and Rotatoria. Their body size varied from ng to µ g of protein nitrogen. Oxygen consumption was linearly related to body size at 11°C or higher, but proportional to the 0.86 power of size at 4°C. Similar size relationships applied for N and P excretion. Relationship of oxygen uptake to temperature was virtually identical in well fed Cyclops vicinus and Daphnia hyalina. The oxygen equivalent of ammonia excretion for protein catabolism was never higher than the measured oxygen consumption; there was no suggestion of an apparent gluconeogenesis or lipogenesis in well fed Cyclops. Relative excretion rates of ammonia and phosphate were related to feeding level. The lowest rates of ammonia excretion were at low natural levels of feeding while they increased both in fasting and well fed animals. Relative phosphate excretion rates increased with increasing food concentration, but individual experiments were not comparable. Herbivorous pond plankton had lower N‐excretion rates than carnivorous, which is comparable with planktophagous fish rates published previously.