Critical thermal maxima in aquatic ectotherms

Critical Thermal Maxima (CTMax) is one of the main used techniques to infer thermal tolerance of a certain organism. Aquatic animals, which are mainly ectotherms, are believed to present growing CTMax from poles towards the equator while their thermal tolerance, in relation to their environmental temperature would present the opposite trend. In this work such pattern is analysed in a global scale by performing metanalysis with previous work data. Also, differences between organisms living in fresh and saltwater ecosystems and between different taxa were assessed. Finally, the effect of other stressors over the thermal tolerance is compiled and discussed. It was possible to prove that, as it has been proposed, CTMax values have an inverse relation with thermal tolerance being the tropical organisms closer to their limit than in other climates. Also, temperate organisms present, in general, the highest thermal tolerance. Marine animals from the temperate region presented lower CTMax and Thermal Safety Margin (TSM) than freshwater organisms from the same region. Such pattern was not verified on the tropical region. The two mollusc classes: Gastropoda and Bivalvia, presented the highest CTMax and TSM values. Several stress factors other than temperature analysed in previous works presented significant effect. An analysis to the possible nefarious effects of such stressors over thermal tolerance was performed.