In the Classroom
How do fish in the Southern Ocean keep from freezing?


On Global Warming

During the 20th century, global temperatures have increased by approximately 0.5 degrees Centigrade (0.9 degrees Fahrenheit), possibly as a result of man-made greenhouse gases. However, temperature changes on a regional basis are more complex. The polar regions are particularly important to our understanding of global change because they are likely to experience dramatic temperature changes long before the temperate zones. For example, the mean air temperature along the Antarctic Peninsula has increased by approximately 2 degrees C (3.6 degrees F) during the past 50 years, and some climate models predict that the polar oceans are likely to warm before those of temperate regions. Thus, the marine organisms of the Antarctic and the Arctic, due to their extreme sensitivity, will serve as environmental �canaries in the coal mine.�

Antarctic marine organisms can live only within extremely narrow temperature ranges (about -2 to +2 degrees C). Antarctic fishes, for example, have long-term upper lethal temperature limits of only +2 degrees C and are therefore extremely vulnerable to any rapid increase in seawater temperatures. The causes of this severe �stenothermality� (from the Greek �steno� = narrow, �thermo� = heat) of Antarctic notothenioids certainly involve multiple physiological and biochemical characters, among which is the inability to generate a �heat-shock� response by expression of genes whose protein products protect against heat-caused cellular damage. Furthermore, many Antarctic marine organisms are apparently living close to the limits of their metabolic capacities, which would drastically limit their ability to cope with elevated temperatures.

By comparing the genomes of Sub- and High-Antarctic notothenioid fishes, we can learn how the stenothermality of the latter evolved and whether the Sub-Antarctic species will be able to respond appropriately to a warming oceanic habitat. This knowledge will enable us make predictions about organismal responses in other regions of the world, which are more complex to study and which are subject to other human influences such as pollution.