In which way does climate change affect the complex interaction in ecosystems? - A perspective for a network of ecological and physiological research

Changes to marine ecosystems caused by climatic conditions show how closely physiological and ecological processes are intertwined. This is described by Prof. Dr. Hans-Otto Pörtner, physiological ecologist at the Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association, in the current issue of the periodical Science.

Results of physiological and ecological research have shown in recent years that the temperature-dependent performance window of a species is crucial for its sensitivity to global warming. It determines its ability to grow, breed, forage and to compete for space or resources against other species under different temperatures. The performance window of animals is determined by their capacity for aerobic metabolism and oxygen supply. These physiological parameters are investigated at the Alfred Wegener Institute on marine animals. “The performance window is limited by temperature and reflects the specialization for the climate”, explains Pörtner. “It shifts with seasonal temperature accommodation and during the change between different life cycles”, he continues.

Scientists were so far able to monitor the following changes in ecosystems: Poleward expansion or shift of bio-geographic areas of distribution, local decrease or extinction of formerly common populations, shifts in the temporal sequence of biological processes, the changing availability of food as well as changing food webs. Many of these changes are primarily caused by temperature. At the same time, a compilation of present results from aquatic animal communities shows that physiological analyses contribute to illuminate the background of these changes and to predict future ecological trends. Not only knowledge of active climate factors, but also of affected physiological mechanisms is necessary to understand the observations of ecological consequences.

The spawn and the larvae of many fish are particularly susceptible while young fish react relatively robust towards temperature oscillations. However, pregnant females which produce the spawn have a narrow performance window which means that they are susceptible to temperature oscillations. Caused by climate change, for instance, the temperature of the North Sea is above the performance optimum for reproducing cod which temperature-wise live at the southern border of their distribution area in the North Sea. This species can relocate towards the North, however. It is important that the performance windows of different species from the same habitat can differ and overlap only in a very limited temperature range. Therefore, climatic shifts affect the interactions between species, for example their competitiveness or the availability of prey in predator-prey-relations. The seasonal sequence of biological processes is also affected by the temperature dependency of the performance windows.

According to emerging knowledge, the temperature window of susceptible species is narrowed by stress factors like the acidification of the oceans. This lets us expect consequences for productivity and geographical distribution. There are some examples where the performance window is already transgressed by climate change: for copepod and eelpouts in the North Sea, for sardines in the Sea of Japan, and for salmons in the Frazer River in western Canada. The consideration of these principles in climate impact research and sundry organisms will be of great importance for the understanding of cause and effect.

The paper “Physiology and climate change” will be published in the periodical Science October 31st 2008.

Notes for Editors:

Your contact person at the Alfred Wegener Institute is Prof. Dr Hans-Otto Pörtner (phone: +49 471 4831-1307; email: Hans.Poertner@awi.de). Your contact person in the public relations department is Folke Mehrtens (phone: +49 471 4831-2007; email: Folke.Mehrtens@awi.de).

The Alfred Wegener Institute carries out research in the Arctic and Antarctic as well as in the high and mid latitude oceans. The institute coordinates German polar research and makes available to international science important infrastructure, e.g. the research icebreaker “Polarstern” and research stations in the Arctic and Antarctic. AWI is one of 15 research centres within the Helmholtz-Association, Germany’s largest scientific organization.