Earth is awfully wet: about 70 percent of the planet is covered by deep, blue expanses of water. But to ocean-faring sea snakes, their briny habitat is an oxymoron: Home is a vast aquatic desert. Creatures like the sea snake were thought to live completely independent of fresh water, by quenching their thirsts through some type of saltwater adaptation like other marine animals. But now researchers have discovered that one species, the yellow-bellied sea snake, in fact relies on rainfalls for drinking water, and in between rains is able to make do in an extreme state of dehydration.
Water, Water Everywhere
Scientists have recently started questioning whether marine vertebrates, such as the sea snake, truly live independently of fresh water. Several species of animals, including sea turtles, bony fishes, dolphins and whales developed specialized adaptations to thrive in saltwater. For example, birds and some marine reptiles have salt glands to excrete excess salts from the water they drink. It was commonly believed that sea snakes adapted to their environment in a similar fashion. But several studies published within the past few years have shown a link between fresh water availability and the distribution of sea snake populations. The only sources of fresh water in the open sea are narrow bands of freshwater lenses that are known to form on the surface of the ocean following heavy rainfalls. Since sea snake populations are often concentrated around these bands of freshwater, researchers believed they depend on the water for survival.
Finding Thirsty Snakes
If this was true, it must mean that sea snakes can survive extreme dehydration. To see if this was indeed the case, researchers captured 500 yellow-bellied sea snakes on the Guanacaste coast off of Costa Rica. They wanted to test if the snakes would drink fresh water immediately following capture. If the snake was thirsty, it was a good sign that it was also dehydrated. The researchers dried the snakes off, weighed them and measured them before giving them fresh water to drink. They found that snakes tended to drink more following periods of low rainfall, and the lighter they were (and thus the more dehydrated they were), the more they drank. Their findings show that sea snakes live in a dehydrated state for several months at a time, due to the length of the dry season on the Guanacaste coast (December through May or June). The researchers published their results this week in the journal Proceedings of the Royal Society B.
Waiting for the Rain
The results show both the tenacity and fragility of yellow-bellied sea snakes, and perhaps other marine snakes. Dehydration at sea could be a unique challenge to marine vertebrates like the sea snake, and may explain their rapidly declining populations in some parts of the world. Further study of these thirsty reptiles could help scientists determine how changing precipitation patterns in tropical oceans will impact these animals.
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