The myth of metabolic cold adaptation: oxygen consumption in stenothermal Antarctic bivalves

Antarctic marine ectotherms are often described as only bring capable of living in a restricted temperature range, i.e. they are stenothermal. However, few data exist demonstrating that for a given group this is the ease. The Antarctic bivalve molluses Laternula elliptica and Limopsis marionensis are similar to other Antarctic invertebrates and can only exist within a temperature window of 6-12 degreesC. This is two to six times smaller than the range fur temperate and tropical bivalves. thus demonstrating their stenothermal nature. Thr possibility of elevated metabolic rate of cold-water ectotherms has been a topic of debate over many years. Recently. the suggestion that metabolic rates must be elevated at low temperatures to overcome constraints has been supported by findings that mitochondrial contents of muscles in ectotherms are higher at low temperatures. Data, presented here for standard or routine metabolic rarer of 41 species of bivalve mollusc from polar, temperate and tropical sites. indicate that oxygen consumption is not elevated at low temperatures. Indeed, analysis of Q(10) coefficients between 0 and 25 degreesC suggests that metabolic rates of polar species may be lower than would be expected by comparison with temperate bivalves.