Australian fish adapts to hotter waters

Some tropical fish can adapt quickly to living in warmer waters, according to a new Australian study which found they have a greater capacity to survive rising sea temperatures than previously thought. Scientists at the government-backed Coral Reef Studies Centre of Excellence found that fish adjusted over several generations to a warmer habitat designed to reflect projected rises in sea temperatures due to global warming. Researcher Jennifer Donelson said when damselfish were exposed to water temperatures 1.5 and 3.0 degrees Celsius higher than current levels, there was a marked decline in their aerobic capacity, affecting their ability to swim fast. "The first generation... really struggled with the increases in temperature," she told AFP Tuesday. "But with two generations maintained at these temperatures we saw that aerobic capacity was improved," she said, adding that it increased to normal levels. Donelson, who is completing her PhD at James Cook University in Townsville, said the research showed some species could adjust faster than the rate of climate change -- a damselfish reaches maturity within two years. "The surprise was really how quickly it happened, that it only took two generations. I think everyone assumes that species will be able to adapt but how long it will actually take has been sort of unknown," she said. The study was designed to look at how fish would cope with the elevated sea temperatures expected by 2050 and 2100. Scientists used likely tropical ocean temperatures based on current trends in man-made carbon dioxide emissions. But they warned the finding applied only to a single coral reef fish species and did not address the more complex issue of the survival of the coral habitat itself, or the impact of warming on the marine food chain. They also noted there were likely to be penalties for fish that successfully adapted to higher temperatures, with initial observations suggesting offspring were smaller than their parents. The rate of reproduction of the fish could also be affected, they said in the research published in the latest issue of the journal Nature Climate Change. The experiment is continuing, but the researchers said they did not expect the fish to be able to adjust to temperatures above the three degree rise.