Zooplankton were collected from 19 stations in Antarctic waters between December 1978 and January 1979. Plankton samples were sorted into individual species and live specimens of 8 species were maintained in an incubator at -0.5 ± 0.5°C and transported to the Australian Institute of Marine Science (AIMS) for laboratory experiments. The remainder of the samples were frozen at -20°C. The live specimens were used for direct measurements of respiration and ammonia excretion rates by a water bottle method. Individual animals were placed in bottles of filtered seawater. The size of the bottle used ranged from 50 to 1000 ml, depending on the size of the animal. After incubation for 24 hours at -0.5°C, a sample of water was drawn for determination of dissolved oxygen concentration and ammonia concentration.Enzyme activity of the respiratory electron transport system (ETS) was determined using frozen specimens of the same species as well as an additional five species. Frozen samples were homogenized with a piece of GF/C filter in ETS B solution and the cell free extracts were incubated at temperatures similar to water temperatures where the animals were collected (± 0.3°C). The same homogenates were used to determine protein concentration. A subsample of animals were freeze dried to determine average body dry weight for each species. The results of protein analysis was expressed as the ratio of protein to dry weight. Respiration rate, ammonia excretion rate and ETS activity were calculated on the basis of average dry weight. Ratios of the respiration rate to ammonia excretion rate (O:N) and ETS activity to respiration rate (ETS:R) were also calculated.Moulting intervals of three specimens of Euphausia superba maintained at -0.5°C were also observed. Measurements of moults were also taken.

This study was initiated to:1. measure respiration and ammonia excretion rates of Antarctic zooplankton2. measure enzyme activity of the respiratory electron transport system (ETS) as an indirect measure of respiration rate3. compare respiration and ammonia excretion rates with published rates for species of the copepod family Calanidae and the Euphausiid genus Euphausia occurring in different temperature regimes.

Live zooplankton taxa used for respiration and ammonia excretion measurements:Pteropoda: Limacina antarcticaCopepoda: Calanus propinquus, Calanus acutus, Metridia gerlachei Euphausiacea: Euphausia superba, Euphausia crystallorophias, Thysanoessa macruraAmphipoda: Parathemisto gaudichaudiiAdditional taxa used to estimate ETS activity from frozen specimens:Ctenophora: Pleurobrachia sp.Pteropoda: Clione antarcticaCopepoda: Calanus tonsus (juvenile), Paralabidocera antarcticaAppendicularia: Oikopleura gaussica