Climate change: fishing runs out of air

Less animals due to warmer water

Eel mother (Zoarces viviparus). © AWI
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Among other things, climate change and the associated global warming are causing higher water temperatures in the oceans. Even in the North and Baltic Seas, these changes have long been felt. The warmer water "robs" many fish but the oxygen to breathe and threatens their stocks. Researchers have found this out in a new study, which they present in the current issue of the science journal Science.

Current shifts in the global climate lead to a change in species composition, especially in the shallow marginal seas of the oceans. The fish stocks are also affected. However, previous studies showing a link between global warming and the decline in fish stocks were based only on statistical data.

For the estimation of future changes, a deeper understanding of the importance of water temperature for the biology of the affected organisms is of fundamental importance. A new study shows that heat-induced oxygen deficiency in fish is the deciding factor influencing stock density.

At the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, scientists from the North Sea Zoarces viviparus from the North Sea investigated the relationship between the seasonal development of water temperature and the density of animals.

The aim was to determine the physiological processes of the fish, which are the first to react to temperature changes. By comparing the ecological field data with the investigations in the laboratory, the scientists were able to prove for the first time that there is a direct correlation between the heat-related oxygen limitation of the eel and the changes in its population density. display

Marine life tolerates only minor changes in environmental conditions

In the course of evolution, marine animals have specialized in the conditions in their habitat and often tolerate only very limited changes. Here, fish from the North Sea, which are exposed to seasonally larger temperature fluctuations, show a higher heat tolerance and wider tolerance windows than, for example, fish from the polar regions, which live at constant low temperatures. Only within their limited tolerance window do the animals show maximum growth and fertility.

The investigations at the Alfred Wegener Institute show that the uptake and distribution of oxygen via respiration and blood circulation essentially determine the tolerance of the animals and function optimally only in a limited temperature window. As the temperature increases, the body's oxygen supply initially deteriorates before other biochemical stress mechanisms react.

Finally, the oxygen supply collapses, the organism is then only viable for a limited time. These findings are an important step in the explanation of climatically induced changes in the ecosystems of the oceans.

(idw - Alfred Wegener Institute for Polar and Marine Research, 05.01.2007 - DLO)