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Some Antarctic fish living in the planet’s coldest waters are able to cope with the stress of rising carbon dioxide levels in the ocean. They can even tolerate slightly warmer waters. But they can’t deal with both stressors at the same time, according to a study from the University of California, Davis.

, published recently in the journal Global Change Biology, of emerald rock cod is the first to show that Antarctic fishes may make trade-offs in their physiology and behavior to cope with ocean acidification and warming waters.

(The research is described in a web feature,  at the 

“In dealing with climate stress, these fish are really bad multitaskers,” said senior author Anne Todgham, an associate professor with the �ٺ���Ƶ Department of Animal Science. “They seem quite capable of coping with increases in CO₂, and they can compensate for some warming. But they can’t deal with both stressors at the same time. That’s a problem because those things happen together — you don’t get CO₂ dissolving in the ocean independent of warming.”

Trade-offs

Antarctic fishes live in water that is typically about -1.9 C (28.6 F). At their field site in Antarctica, the authors exposed emerald rock cod to two temperatures: -1 degree Celsius (30 F) and 2 degrees Celsius (36 F). The latter is the threshold for global warming that the Paris Agreement targets to prevent the most catastrophic impacts of climate change. They also exposed the fish to treatments of three different levels of CO₂ ranging from ambient to elevated projected levels.

Increased CO₂ levels by themselves had little impact on the fish. After a couple of weeks, heart, ventilation and metabolic rates increased with warming. Their behavior also changed with warming. The fish swam less and preferred dark zones, which suggests they were attempting to conserve energy. Then after 28 days, juvenile rock cod were able to compensate for the warming temperatures. However, this temperature compensation only happened in the absence of rising CO₂.

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No colder places to go

While some species are beginning to shift to cooler places to escape warming habitats, polar fish have no colder places to go. They have to cope by using their existing physiology, which the study shows is limited.

Emerald rock cod help form the basis of the Antarctic food web, supporting an ecosystem of species such as emperor penguins and seals.

“The Antarctic has contributed very little to the production of greenhouse gases, and yet it’s one of the places on the planet receiving the most impact,” Todgham said. “I feel we have responsibility to care about the spaces that are so fragile. If we can provide reservoirs of areas that are less stressful to plants and animals through protecting natural places, we can buy ourselves some time to deal with things like climate change that will take a long time to get in line.”

The study’s authors include lead author and Ph.D. student Brittany Davis, Erin Flynn and Nann Fangue of �ٺ���Ƶ, Frederick Nelson of �ٺ���Ƶ and Howard University; and Nathan Miller from San Francisco State University.

The study was funded through grants from the Division of Polar Programs, National Science Foundation, and University of California Agricultural Experiment Station.