Captured sea kraits refuse to drink salt water even when they are thirsty, and go looking for fresh water.
"Our experiments demonstrate they actually dehydrate in sea water, and they'll only drink fresh water, or highly diluted brackish water with small concentrations of salt water - 10 to 20 percent," said Harvey Lilywhite, zoologist, Univeristy of Florida.
Harold Heatwole, professor of zoology and sea snake expert at North Carolina State University (NCSU), termed Lillywhite's conclusion "a very significant finding. This result probably holds the key to understanding the geographic distribution of sea snakes," Heatwole said.
Lillywhite believes the sea snakes that spend their lives in the open ocean drink water from the "lens" of freshwater that sits atop saltwater during and after rainfall, before the two have had a chance to mix.
That would explain why some seawater lagoons, where the waters are calmer due to protection from reefs, are home to dense populations of sea snakes - the freshwater lens persists for longer periods before mixing into saltwater.
In lab studies, Lilywhite's team kept snakes caught in the wild near Orchid Island, Taiwan, away from fresh water for two weeks. At the end of that period, dimpling of the snakes' scales indicated they were dehydrated.
The researchers weighed the snakes, freed them in saltwater tanks for up to 20 hours, then weighed them again. None gained appreciably, indicating they didn't drink, despite their thirst, according to a university statement.
But when the researchers freed the snakes to swim in freshwater tanks, most immediately drank significant amounts. More experiments revealed the snakes would drink only fresh water or highly diluted salt water.
The research may help explain why sea snakes tend to be most common in regions with abundant rainfall, Lillywhite said. Because global climate change tends to accentuate droughts in tropical regions, the findings also suggest that at least some species of sea snakes could be threatened now or in the future, he added.
"There may be places where sea snakes are barely getting enough water now," he said. "If the rainfall is reduced just a bit, they'll either die out or have to move."
Sea snakes are members of the elapid family of snakes that also includes cobras, mambas and coral snakes. They are thought to have originated as land-dwelling snakes that later evolved to live in oceans.
These findings will appear online in Physiological and Biochemical Zoology.