METABOLIC RATES OF THE ANTARCTIC AMPHIPOD Gondogeneia antarctica AT DIFFERENT TEMPERATURES AND SALINITIES

Changes in environmental factors may deeply affect the energy budget of Antarctic organisms as many of them are stenothermal and/or stenohaline ectotherms. In this context, the aim of this study is to contribute to knowledge on variations in the energy demand of the Antarctic amphipod, Gondogeneia antarctica as a function of temperature and salinity. Experiments were held at the Brazilian Antarctic Station Comandante Ferraz, under controlled conditions. Animals collected at Admiralty Bay were acclimated to temperatures of 0 degrees C; 2.5 degrees C and 5 degrees C and to salinities of 35, 30 and 25. Thirty measurements were made for each of the nine combinations of the three temperatures and three salinities, totalling 270 measurements. Metabolic rates were assessed by oxygen consumption and total nitrogenous ammonia excretion, in sealed respirometers. When acclimated to salinities 30 or 35, metabolic rates at 0 degrees C and 2.5 degrees C were very similar indicating a possible mechanism of metabolic compensation for temperature. At 5.0 degrees C, however, metabolic rates were always higher. Lower salinities enhanced the effects of temperature on metabolism and ammonia excretion rates. The physiological adaptations of individuals of G. antarctica suggest adaptive mechanisms for energy saving, adjusted to an environment with stable conditions of temperature and salinity. Little is known about the joint effects of salinity and temperature and this study is an important contribution to the understanding of the mechanism of polar organisms in their adaptation to both factors.