Physiologische Grundlagen temperaturabhängiger Biogeographie bei marinen Fischen

The physiological mechanisms limiting thermal tolerance and therefore geographical distribution of ectothermal organisms were investigated in the light of global warming. Comparative studies carried out on marine ectotherms from a latitudinal cline indicate that the limits of thermal tolerance are linked with temperature induced adjustments in aerobic scope and capacity depending on latitude or seasonal temperature acclimatisation. Aerobic mitochondrial and enzymatic capacities were investigated in liver of different cod populations (Gadus morhua, North Sea, Norwegian coast and Barents Sea) and of two eelpout species (Zoarces viviparus, North Sea and Pachycara brachycephalum, Antarctica). Cold acclimation and cold adaptation led to an increase of the aerobic capacity due to an increase in liver size accompanied by an increase in mitochondrial protein content. Differences in temperature induced adjustments of mitochondrial metabolism were found between cold adapted stenotherms and cold adapted eurytherms. The results indicate that elevated standard metabolism and reduced growth in the cold may be attributed to elevated proton leakage correlated with increased mitochondria densities.The hypothesis of an oxygen limited thermal tolerance due to limitations in cardiovascular performance was tested in G. morhua. Thermal limitation may set in before critical temperatures are reached, characterised by decreased venous PO2 owing to onset of a progressive mismatch between oxygen demand and circulatory performance. In conclusion, progressive cooling or warming brings cod from a temperature range of optimum cardiac performance into a pejus range, when aerobic scope falls before critical temperatures are reached. The temperature induced limitation in cardiovasular performance is discussed in the light of geographical distribution limits found for G. morhua in nature and might be the reason for the predicted northern shift in the distribution of North Sea cod with global warming