Acclimation and thermal tolerance in Antarctic marine ectotherms

Antarctic marine species have evolved in one of the coldest and most temperature-stable marine environments on Earth. They have long been classified as being stenothermal, or having a poor capacity to resist warming. Here we show that their ability to acclimate their physiology to elevated temperatures is poor compared with species from temperate latitudes, and similar to those from the tropics. Those species that have been demonstrated to acclimate take a very long time to do so, with Antarctic fish requiring up to 21-36 days to acclimate, which is 2-4 times as long as temperate species, and invertebrates requiring between 2 and 5 months to complete whole-animal acclimation. Investigations of upper thermal tolerance (CT(max)) in Antarctic marine species have shown that as the rate of warming is reduced in experiments, CT(max) declines markedly, ranging from 8 to 17.5 °C across 13 species at a rate of warming of 1 °C day(-1), and from 1 to 6 °C at a rate of 1 °C month(-1). This effect of the rate of warming on CT(max) also appears to be present at all latitudes. A macrophysiological analysis of long-term CT(max) across latitudes for marine benthic groups showed that both Antarctic and tropical species were less resistant to elevated temperatures in experiments and thus had lower warming allowances (measured as the difference between long-term CT(max) and experienced environmental temperature), or warming resistance, than temperate species. This makes them more at risk from warming than species from intermediate latitudes. This suggests that the variability of environmental temperature may be a major factor in dictating an organism's responses to environmental change.