Seasonal excretion rates of macrozooplankton from the Swedish west coast

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Abstract
Weight‐specific excretion rates of ammonium, urea, inorganic phosphate, and total dissolved phosphorus by 19 species of zooplankton were measured during March–October 1981. Excretion rates of two copepods Calanus finmarchicus and Metridia longa showed similar trends during spring and summer, but diverged in autumn when C. finmarchicus had much lower rates. Excretion rates of most species were highest in spring and relatively low during summer. The high rates of excretion in spring corresponded with the spring phytoplankton bloom, but later blooms did not affect the excretion rates of the zooplankton. The average excretion rates varied considerably between species; ammonium from 3.2 to 68.1, urea from 0.9 to 6.3, inorganic phosphate from 0.3 to 8.2, and organic phosphorus from 0 to 3.5 nmol excreted per mg of body protein per hour. The average atomic N:P ratio ranged between 2.4 and 46.3, but was Sagitta elegans. Estimation of the regenerative importance of nitrogen and phosphorus from macrozooplankton excretion indicated that between 4 and 50% of the phytoplankton nitrogen demands could be fulfilled, with the highest percentage demand being met during autumn. For phosphorus the range was 14–102% of the phytoplankton requirements.