Crocodiles Might Not Be Climate Change–Proof After All
Even saltwater crocodiles aren’t safe from climate change.
The species is considered one of the most resilient in Australia, but new research shows that it spends less time underwater when temperatures increase, and that could put its survival in jeopardy as heat records continue to be broken.
Crocodiles dive for food, protection, socializing, and even a catnap. They can typically stay underwater for 10- to 15-minute periods and up to 30 minutes if they are trying to hide from a threat. On average, a crocodile spends around 11 hours a day submerged.
To see how climate change would affect Australia’s saltwater crocs, researchers at the University of Queensland studied juvenile crocodiles in three pools heated to different temperatures.
The first pool was set to the region’s current summer water temperature of 82 degrees Fahrenheit. The second was set to 88 degrees—what scientist expect water temperatures to average under moderate climate change. They heated the third pool to 95 degrees, what the region could see under a worst-case climate scenario.
Essie Rodgers, the study’s lead author and a Ph.D. student at the University of Queensland, quickly saw a change in the crocodiles’ behavior.
“Acute increases in water temperature resulted in significantly shorter crocodile dives,” Rodgers said in a statement. “Their submergence times halved with every 3.5-degree Celsius increase in water temperature.”
Crocodiles are ectothermic: They rely on external elements like the sun to regulate their body temperature. Temperatures above 100 degrees can be lethal for the animals, Rodgers said. During heat waves, they rely on the cooler waters to keep them from overheating. As waters warm as climate change accelerates, crocodiles could be forced to migrate south or face extinction.
“We thought that crocodiles—like many animals—would adjust to temperature changes so life continues,” said Craig Franklin, a professor at the University of Queensland’s school of biological sciences. “However, we were surprised to find they had little capacity to compensate for water-temperature changes and seemed to be hardwired to operate at certain temperatures.”
Crocodiles have survived for 250 million years. Fossil records show that prior to the last great extinction 65 million years ago, crocodiles roamed much more of the planet than they do today, with a range that extended into much of North America, Europe, and Russia.
Crocodilians such as caimans, alligators, and gavials eventually migrated to the warmer waters of the southern hemisphere, where they mostly remain.
For Australia’s saltwater crocodiles, the changing temperatures could mean the animals might start searching for cooler waters, heading farther south than their known range.
Franklin said more testing needs to be conducted to get a better understanding of how climate change could affect crocodiles’ prey.
“We are not sure what this means, but it’s likely that if the water is too hot, crocodiles might move to cooler regions or will seek refuge in deep, cool water pockets to defend their dive times,” he said.