Like amphibians, reptiles, and all invertebrates, fish are ectotherms whose body temperatures are determined by the ambient temperature. Many fish species both in Sweden and elsewhere in the world normally experience major seasonal variations in temperature, and are well adapted to cope with them. Fish in the Antarctic live in an extremely cold and, in many cases, stable environment.

The ocean around Antarctica is cold, with temperatures of roughly -1.9°C, which is just above the freezing point of ocean water. This means that the fishes’ body temperature is also -1.9°C. To avoid freezing, the fish must produce an antifreeze protein, as do fish species in the northern polar regions, where the water temperature can also be extremely low during the winter months. How do the heart, vascular system, and respiration function at such low temperatures, and how are they regulated?

Recent research has also addressed the ways in which global warming could affect fish in the Antarctic that have lived under stable cold conditions for millions of years.

The year’s expedition was divided into three subprojects focusing, respectively, on the effects of natural blood doping, the effects of temperature on intestinal function, and the effects of temperature on the respiration and circulation of Glyptonotus antarcticus.

In the subproject concerning natural blood doping, we looked at how blood pressure and the heart are affected when fish raise their hematocrit levels (i.e., the proportion of red cells in the blood) by contracting their spleens. We had previously demonstrated that one fish species has a remarkable ability to store red blood cells in its spleen and use them to raise its hematocrit level when it needs to increase its oxygen transport. For the first time we can now see the effects of this on the heart and vascular system in real time. Our hypothesis was that an elevated hematocrit level would increase the load on the heart, as it leads to increased blood viscosity, and we can now quantify this.

In the second subproject, we studied the effects of temperature on the barrier function of the intestinal tract. This was done both in connection with acute temperature increases and after a number of weeks of acclimatization to a higher temperature.

In the third subproject, we studied the effects of both temperature and what is known as “ocean acidification”, i.e., the lowering of ocean pH due to increasing carbon dioxide levels in the atmosphere. We acclimatized G. antarcticus to various aquatic temperatures and pH values to simulate Intergovernmental Panel on Climate Change (IPCC) scenarios of future water temperature and pH trends. The hypothesis was that these large crustaceans may have evolved in cold water due to a limitation in their oxygen transport, and that they would consequently be particularly sensitive to temperature increases. We studied both respiration and heart function in the various acclimatization groups of these creatures. We found, to our great surprise, that this species encounters no major problems in coping with a moderate increase in water temperature.

The expedition was a cooperative effort between the National Science Foundation (NSF) and the Swedish Polar Research Secretariat. McMurdo Station in the Ross Sea served as the base for our fieldwork for six weeks.