SEASONAL EXCRETION RATES OF MACROZOOPLANKTON FROM THE SWEDISH WEST-COAST

Weight-specific excretion rates of ammonium, urea, Pi and total dissolved P by 19 spp. of zooplankton were measured during March-Oct. 1981. Excretion rates of 2 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 3.2-68.1, urea 0.9-6.3, Pi 0.3-8.2 and organic P 0-3.5 nmol excreted/mg of body protein/h. The average atomic N:P ratio ranged between 2.4-46.3, but was < 20 for all species except Sagitta elegans. Estimation of the regenerative importance of N and P from macrozooplankton excretion indicated that between 4-50% of the phytoplankton N demands could be fulfilled, with the highest percentage demand being met during autumn. For P the range was 14-102% of the phytoplankton requirements. [The other zooplankton studied were Calanus hyperboreus, Chiridius armatus, Euchaeta norvegica, Balanus sp., Boreomysis arctica and E. hamata.] Conchoecia borealis elegans, Meganyctiphanes norvegica, Parathemisto abyssorum, Pasiphaea multidentata, Aurelia aurita, Eutonina indicans, Beroe cucumis, Pleurobrachia pileus, Tomopteris helgolandica, Eukrohnia batypelagica; and E. hamata.