Everyone’s favorite marine mammal likes to keep cool, but scorching seawater appears to be wreaking havoc with dolphins in some parts of the world, a new study suggests.
Scientists first noticed the problem after a 2011 heat wave in Australia: Unusually warm seawater off Australia’s western coast that year was followed by a significant decrease in dolphin births over the next six years. By tracking hundreds of dolphins during that time, scientists also found the warmth had dropped the mammal’s survival rate by 12 percent.
“The extent of the negative influence of the heat wave surprised us,” said study lead author Sonja Wild in a statement. “It is particularly unusual that the reproductive success of females appears to have not returned to normal levels, even after six years,” said Wild, a Ph.D. student at the University of Leeds in the U.K.
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The dolphins studied live in Shark Bay, a UNESCO world heritage site in Western Australia. During that 2011 hot spell, temperatures in the bay were as much as 7 degrees Fahrenheit above average, scientists said. The extreme warmth damaged seagrass, a key cog in the bay’s ecosystem that provides food and shelter for its inhabitants.
“Our findings suggest that extreme weather events may be too sudden or disruptive for even highly adaptable animals to respond,” study co-author Simon Allen of the University of Bristol in the U.K. said.
Fish species in the ocean are also threatened by climate change: A study in February found that warming oceans have shrunk the populations of many fish species around the world.
Farewell, fish-and-chips?: Atlantic cod, many other fish dwindling as globe warms
Some good news from Monday’s study: The heat wave did not have the same effect on all dolphins. Dolphins that use sponges as tools – a technique that helps dolphins locate food in deep water – were not as affected as those that don’t use this technique.
Still, Wild said the declines in dolphin populations “are a stark reminder of the negative effects of climate change.”
In fact, even beyond dolphins, climate change may have more far-reaching consequences for the survival of many other marine mammal species than had been previously thought. “Marine heat waves are likely to occur more frequently in the future due to climate change,” said study co-author Michael Krützen, an anthropologist from the University of Zurich in Switzerland.
“This is worrying not only for the long-term prospects of marine mammal populations but also for the entire oceanic ecosystems,” he said.
The study was published Monday in the peer-reviewed science journal Current Biology.