Sea snakes are a diverse group of over 70 marine reptile species, primarily inhabiting the warm coastal waters of the Indian and Pacific Oceans. These creatures have undergone significant evolutionary changes to adapt to a fully aquatic lifestyle. While they are reptiles with terrestrial ancestors, their aquatic adaptations raise questions about their ability to survive outside their oceanic home. Their specialized biology explains why most sea snakes are rarely found on land.
Aquatic Adaptations of Sea Snakes
Sea snakes possess several adaptations that allow them to thrive in marine environments, yet these features make terrestrial movement challenging. Many species have laterally compressed bodies and paddle-like tails, which are efficient for propulsion through water. This specialized body shape, along with reduced or absent ventral scales, hinders their ability to grip and move effectively on solid ground.
Despite living in water, sea snakes breathe air using a single elongated lung that extends the length of their body. This lung stores oxygen for prolonged dives and assists with buoyancy control. Many sea snake species can also absorb a portion of their oxygen requirements directly through their skin, a process known as cutaneous respiration, which extends their underwater endurance.
Life in a saline environment necessitates mechanisms for managing salt intake. Sea snakes have evolved sublingual salt glands, located under their tongue, which excrete excess salt ingested from their diet or surrounding seawater. This physiological adaptation is important for maintaining their internal water balance in a marine habitat. The permeable nature of their skin, while aiding in oxygen absorption underwater, also makes true sea snakes susceptible to dehydration when exposed to air. This vulnerability means they cannot survive for extended periods out of water.
Occasional Land Encounters
While most true sea snakes are largely helpless on land, a group known as sea kraits (genus Laticauda) regularly venture ashore. Unlike their aquatic relatives, sea kraits have retained cylindrical bodies and enlarged ventral scales, allowing them to move with ease on terrestrial surfaces. These semi-aquatic snakes come to land for biological necessities, such as shedding their skin, resting, and drinking freshwater. Sea kraits are oviparous, meaning they must return to land to lay their eggs in terrestrial nests, often in rocky crevices or caves.
True sea snakes, which give birth to live young at sea, only come ashore under duress or by accident. Strong currents, storms, or illness can wash these specialized marine reptiles onto beaches, where their survival time is limited. Once stranded, their paddle-like tails offer little traction, making them unable to move back to the water.
For most true sea snakes, survival on land is measured in hours rather than days, due to their inability to move and dehydration. Stranded individuals are in poor physical condition and may struggle with maintaining blood pressure outside of water. Therefore, while sea kraits routinely undertake brief terrestrial forays, the majority of sea snake species are unequipped for a prolonged existence away from their aquatic environment.