(Phys.org) —A team of researchers with members from France, the U.S. and Australia, has found that the yellow-bellied sea snake (Hydrophis platurus) is able to survive out in the ocean because its ability to survive severe dehydration. In their paper published in Proceedings of the Royal Society B: Biological Sciences, the team describes how they captured over 500 of the snakes and tested them to determine how they survived being so long at sea without access to fresh water.
The yellow-bellied sea snake lives primarily in the sea, which means it has to get all of its food and water from the ocean. The problem is, unlike sea turtles, it doesn't have the ability to simply drink sea water and filter out all the salt. Instead, it survives, the researchers in this new effort report, by not drinking at all for months at a time. Living as it does off the coast of Costa Rica, the snake is dependent on fresh water from rainfall, but only during the rainy season—the fresh water sits for a time atop the heavier saltwater below, the snake surfaces and swallows it, bloats up and then doesn't have to drink again for months. The trick is in surviving severe dehydration—the team found some specimens lost up to 18 percent of their body mass while waiting for rain.
The researchers discovered this unique ability by capturing and examining specimens in their labs, caught at different times of the year. To test for thirstiness, the snakes were put in fresh water tanks. To assess how much water they were storing, several were weighed, then killed and baked in ovens to remove all the water held inside them, then weighed again. Some were also dissected.
The researchers found that the snakes do have some ability to eliminate salt—small glands around their tongues expel salt taken in during eating, or to remove some salt from the fish they eat. The glands were nowhere near efficient enough to allow the snakes to drink saltwater however, thus, their refusal to do so. They also found that the snakes' skin prevented salt from being absorbed into their bodies.
The researchers also noted that the snakes' technique for surviving at sea makes it particularly vulnerable to changes in its environment such as less frequent rainfall. This, they suggest might reveal why it is that scientists have been finding that sea snake populations are declining as global warming causes changes to rain patterns across the globe.
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More information: Pelagic sea snakes dehydrate at sea, Proc. R. Soc. B 7 May 2014 vol. 281 no. 1782 20140119. rspb.royalsocietypublishing.org/content/281/1782/20140119
Secondarily marine vertebrates are thought to live independently of fresh water. Here, we demonstrate a paradigm shift for the widely distributed pelagic sea snake, Hydrophis (Pelamis) platurus, which dehydrates at sea and spends a significant part of its life in a dehydrated state corresponding to seasonal drought. Snakes that are captured following prolonged periods without rainfall have lower body water content, lower body condition and increased tendencies to drink fresh water than do snakes that are captured following seasonal periods of high rainfall. These animals do not drink seawater and must rehydrate by drinking from a freshwater lens that forms on the ocean surface during heavy precipitation. The new data based on field studies indicate unequivocally that this marine vertebrate dehydrates at sea where individuals may live in a dehydrated state for possibly six to seven months at a time. This information provides new insights for understanding water requirements of sea snakes, reasons for recent declines and extinctions of sea snakes and more accurate prediction for how changing patterns of precipitation might affect these and other secondarily marine vertebrates living in tropical oceans.