| In the present study, metabolic responses of various Antarctic marine species to two parameters, primary productivity and temperature, were investigated. The pulsed productivity and the constant cold temperature have acted as selective pressures since the isolation and cooling of Antarctica and, in response, various physiological and biochemical adaptations have developed to allow the present marine fauna to thrive in this unique environment. To examine the influence of the spring ice-edge bloom on the metabolism of zooplanktonic and micronektonic organisms, oxygen consumption rates were determined on 29 species of zooplanktonic and micronektonic organisms from three zones of widely different ice coverage and chlorophyll biomass: pack-ice (pre-bloom), ice-edge (bloom), open water (post bloom). Higher metabolic rates were observed in the primarily herbivorous copepods, Calanoides acutus, Rhincalanus gigas, and Calanus propinquus in regions of higher primary production: ice-edge and open water. The carnivorous Euchaeta antarctica showed a similar pattern. The omnivorous copepods Metridia gerlachei and Gaetanus tenuispinus showed no changes in metabolism between zones. No differences in metabolic rates between zones were observed for micronektonic species, probably due to their greater ability to move within the different sub-regions of the marginal ice zone. Biochemical metabolic indicators were also determined in micronektonic species using frozen specimens: citrate synthase (CS) activity and malate dehydrogenase (MDH) activities, indicators of aerobic metabolism; RNA:DNA ratio, an indicator of growth; and protein and water content for evidence of nutritional status. MDH activity was the best predictor of metabolism, followed by CS activity. In conclusion, the effects of the ice-edge bloom on metabolism were greater on weaker swimmers and primarily herbivorous species, and thus the responses depend on the animal's trophic position and life style.; Long-term adaptation to the cold, nearly isothermal waters close to the Antarctic continent was investigated in several nearshore species. The controversial concept of cold adaptation, which states that polar, temperate, and tropical ectotherms exhibit similar metabolic rates at normal habitat temperature, was tested at the biochemical level using the activity of citrate synthase (CS) and lactate dehydrogenase (LDH) in the brain of Antarctic, temperate, and tropical fishes. Since within any climatic region levels of enzyme in the brain are independent of life style, difference in activity could be attributed to cold adaptation and not to differences in activity level or aspects of life habit. Activity of CS in the brains of Antarctic fishes was 1.4 times higher than in brains of temperate species and 1.9 times higher than that in tropical species at the common measurement temperature of {dollar}rm 10spcirc C.{dollar} LDH activity in the brain of Antarctic fishes at {dollar}rm 10spcirc C{dollar} was 2.2 and 2.5 times higher than that in temperate and tropical species respectively. Differences were significant for both enzymes. The data suggest a high degree of metabolic compensation in Antarctic fish brains, supporting the existence of the phenomenon of cold adaptation. |
