Oxygen uptake, ammonia and phosphate excretion and chemical composition of Antarctic zooplankton (RV Kaiyo Maru Cruise)

Zooplankton were collected from 15 stations in Antarctic waters, adjacent to Wilkes Land in January 1980. The location, type of net used and the sea surface temperature were recorded for each plankton tow. Water from each sampling site was collected and filtered for use in experiments. Undamaged animals were sorted by species and maintained separately until experiments commenced, usually between 8 to 24 hours later.

Of the 14 species collected, the following were classified as herbivore filter-feeders: the pteropods, Limacina antarctica and Cleodora sulcata; the copepods, Calanus propinquus and Metridia gerlachei; the Euphausiids, Euphausia surperba and Euphausia triacantha; and the salps, Ihlea racovitzai and Salpa thompsoni. The remaining species, classified as carnivores were: the ctenophore, Beroe sp.; the pteropod, Clione antarctica; the polychaete, Tomopteris carpenteri; and the amphipods, Parathemisto gaudichaudii, Viblia antarctica and Hyperia gaudichaudii.

Oxygen uptake, ammonia excretion and phosphate excretion measurements were made on board the RV Kaiyo Maru, using a water-bottle method. Zooplankton were placed in bottles of filtered seawater. The size of the bottle used ranged from 250 to 2000 ml, depending on the size of the animal. Larger individuals were incubated individually, while for smaller species, up to 30 individuals were placed in a bottle. Bottles were wrapped in aluminium foil to exclude light and placed in a water bath to maintain a constant temperature, which was slightly below the surface temperature at the sampling site. After incubation for 24 hours, duplicate water samples were drawn for dissolved oxygen, and ammonia and phosphate measurements. The animals remaining in the bottles were collected and frozen at -50°C for later determination of dry weight, by freeze drying, and elemental analysis.

For elemental analyses of carbon (C), nitrogen (N) and Phosphorous (P), dried specimens were ground, pooled by experiment or body size group (when the range of body sizes was large) for each species. C and N were measured with a Perkin Elmer Model 240 elemental analyser, using acetanilide as a standard. P analysis required samples to be digested in 50% (v/v) sulphuric acid for 1 hour at close to 100°C and neutralized by KOH. P was then measured as phosphate using the molybdate method.