Routine metabolism and ammonia excretion of the Antarctic amphipod Waldeckia obesa in two different temperatures

Abstract

Mean and specific oxygen consumption and ammonia excretion were measured at 0ºC and 3ºC, in the Antarctic amphipod Waldeckia obesa collected in Admiralty Bay, King George Island, Antarctica. Experiments were carried out at the Brazilian Antarctic Station "Comandante Ferraz" and at the Laboratory of Polar Ecology of the Oceanographic Institute of São Paulo University. Individuals ranging from 120 mg to 620 mg and from 40 mg to 690 mg were employed in experiments at 0ºC and 3ºC, respectively. Within this range of weight, mean oxygen consumption varied from 2.22µ1/h to 10.81µ1/h and specific consumption from 0.011µ 1/mg/h to 0.018µ 1/mg/h, at 0ºC. At 3ºC, mean oxygen consumption varied from 1.83 µ1/h to 14.9µi/h and specific consumption from 0.033µ1/mg/h to 0.022µ1/mg/h. Q10 value calculated from average oxygen consumption was 6.95. Mean ammonia excretion, at 0ºC, varied from 13.84 ng.at/h to 55.34 ng.at/h and specific excretion from 0.090 ng.at/mg/h to 0.042 ng.at/mg/h. At 3ºC, mean ammonia excretion varied from 5.11 ng.at/h to 38.33 ng.at/h and specific excretion from 0.088 ng.at/mg/h to 0.059 ng.at/mg/h. 0:N ratio indicates that a mixture of protein and lipids is utilized for catabolism. At 3ºC, however, there is a tendency to increase the lipid contribution for the substrate. Oxygen consumption of Waldeckia obesa at 0ºC is very low and is in accordance with the values reported by some other authors. These data and others recent results found in the literature indicate the fragility of the "metabolic cold adaptation" hypothesis, that assumes that marine Antarctic ectotherms have high metabolic rates, as an evolutive adaptation to low temperatures. Oxygen consumption and ammonia excretion data could be extrapolated to populational parameters giving support for the studies on the ecological role of these animals in their ecosystem.