Sea snakes, fascinating reptiles adapted to marine environments, breathe air. Like all reptiles, these creatures possess lungs and must periodically surface to inhale oxygen from the atmosphere. Their lineage traces back to terrestrial ancestors, yet they have evolved remarkable features enabling an almost entirely aquatic life. This adaptation to ocean dwelling still requires atmospheric air.
How Sea Snakes Breathe
Sea snakes have specialized respiratory anatomy for breathing in water. Their nostrils are positioned dorsally, or on top of the snout, allowing the snake to break the surface with minimal exposure. These nostrils are equipped with valve-like flaps of spongy tissue that seal tightly when submerged, preventing water from entering.
A single, elongated lung extends nearly the entire length of their body, a common reptilian feature but particularly adapted in sea snakes. This extensive lung serves dual purposes: gas exchange and buoyancy control. The glottis, the opening to the windpipe, can be closed underwater and drawn forward to the roof of the mouth, aiding quick breaths at the surface. When surfacing, sea snakes use intercostal muscles to expand their chest and draw in air; some can also use their buccal cavity to pump air into their lungs.
The rear portion of this extended lung often has less vascular tissue, primarily functioning as an air reservoir and a hydrostatic organ. By adjusting the air volume, sea snakes can precisely regulate their buoyancy, allowing them to ascend, descend, or remain at a specific depth without expending much energy. This mechanism aids in hunting and navigating their underwater habitat.
Remarkable Adaptations for Life in the Ocean
Despite their reliance on atmospheric oxygen, sea snakes have several specialized adaptations for extended underwater periods. One such adaptation is cutaneous respiration, where some species absorb oxygen directly through their skin. This skin breathing can contribute significantly to their oxygen needs, with some species absorbing up to 33% of required oxygen and releasing up to 90% of carbon dioxide through their skin during dives. Their skin is thinner and more permeable to gases than land snakes, supported by a dense network of capillaries just beneath the surface.
Beyond skin respiration, some sea snake species, like the blue-banded sea snake, have a modified cephalic vascular network (MCVN) on their head. This network of blood vessels, located under the skin of the forehead and snout, allows them to absorb additional oxygen directly from the water. This oxygen can then be transported to the brain, providing a complementary supply during prolonged submergence.
Sea snakes can also control their metabolic rate, slowing it down to conserve oxygen during dives. This allows them to prolong their time underwater significantly, with some species remaining submerged for up to 8 hours. This metabolic control is important when foraging or seeking refuge in deeper waters.
Sea snakes have specialized sublingual glands located under their tongue that excrete excess salt. These glands are essential for managing the high salt intake that occurs when living in a marine environment and consuming prey. These adaptations collectively contribute to their ability to thrive, hunt, and navigate effectively in the ocean, making them successful marine predators.