Warming Oceans Threaten Livelihood of Fishing Communities as Species Struggle to Cope

As ocean temperatures increase, fish living in ecosystems around the equator may face serious threats, according to new research in the journal Global Change Biology, which reports that just slight increases in water temperature may cause local fish to swim to more suitable waters, which could impact fishing communities in Southeast Asia.

Jodie Rummer, a coral reef expert at James Cook University in Australia, studied six common species of fish living along equatorial coral reefs and the effects of warming water on the fishes' ability to survive.

"Our studies found that one species of fish could not even survive in water just three degrees Celsius warmer than what it lives in now," Rummer said.

The temperature sensitivity, Rummer suggested, is likely because the fish in warm equatorial waters only experience a narrow range of temperature over the course of their lives and have likely evolved to preform best at those temperatures.

Rummer said equatorial fish species are most at risk from climate change because of the narrow temperature range they are accustomed to. The projected 2-3 degree Celsius temperature increase of the oceans by the end of this century could pose significant risks to certain fish species.

"Such an increase in warming leads to a loss of performance," Rummer said. "Already, we found four species of fish are living at or above the temperatures at which they function best."

To calculate how well fish preform at various water temperatures, Rummer and her colleagues tested the rates at which fish use oxygen, which fuels metabolism, across a range of water temperatures. Their analysis revealed that as the water warms the fishes' performance drops. In a lab setting, where the tests were preformed, this does not threaten the fish. But in the wild, when the fish needs to be preforming at a high level in order to catch prey and avoid being eaten itself, the temperature of the water is crucial for its survival.

Rummer said that many fish species are already living close to their thermal limits and that as waters continue to warm, the fish may migrate to more suitable temperatures, which could have an effect beyond the ocean.

"This will have a substantial impact on the human societies that depend on these fish," Rummer said, noting communities in Indonesia and Papua New Guinea that rely on the types of fish in the study.

"This is particularly urgent when considering food security for human communities," Rummer added.