Sea snake (marine elapid)

Anatomy and adaptations

Sea snakes show multiple anatomical specialisations for an aquatic lifestyle. Typical traits include a laterally compressed body and a broad, flattened tail that functions as a paddle for propulsion. Most species have valved nostrils that close underwater, reduced ventral scales that limit traction on land, and lungs that are elongated to aid buoyancy and extended breath-holding dives. A specialised sublingual salt gland helps remove excess salt taken in while swallowing seawater. Dentition is generally elapid (fixed front fangs) and venom is adapted to subduing fish and eels.

Distribution and habitat

Sea snakes inhabit warm coastal waters across the Indo-Pacific region. Their range extends through much of the Indian Ocean and the western and central Pacific, where they occupy coral reefs, seagrass beds, mangroves and open coastal seas. They are largely absent from the Atlantic Ocean; the Atlantic coastline has no native, truly marine sea snake faunas (absence in the Atlantic). They are uncommon or absent around much of the North American Pacific coast north of the eastern tropical Pacific, with records limited compared with tropical Indo-Pacific waters (North American coast, Gulf of California region exceptions).

Behaviour, diet and life history

Most sea snakes are fully aquatic and rarely come ashore. They breathe air and must surface periodically, but they can remain submerged for extended periods while hunting. Diets typically consist of fish and eels, and some species specialise on particular prey types. Reproductive strategies vary: the majority of true sea snakes are viviparous (giving birth to live young in the water), while some semiaquatic genera, such as Laticauda, retain the ancestral habit of coming onto land to lay eggs and move more readily onshore.

Evolution and relationships

Sea snakes evolved from terrestrial elapid ancestors that colonised coastal habitats and gradually adapted to life in the sea. Molecular and morphological studies indicate a radiation of marine-adapted forms from land-dwelling snakes (evolutionary origin). Different lineages display varying degrees of aquatic adaptation, from fully marine, live-bearing snakes to semi-marine, egg-laying species that still use terrestrial habitats.

Human interactions and conservation

Sea snakes have potent venom, well adapted for subduing fish, and some species can pose a risk to people if handled or provoked; however, they are generally not aggressive. Human impacts include habitat degradation (loss of coral reefs and seagrass), pollution, and incidental capture in fisheries. Conservation status varies among species, with some widespread and common, others restricted and threatened by local changes. Practical measures to reduce harm include avoiding handling, protecting coastal habitats, and monitoring bycatch. For general references and further reading see specialist sources and regional guides (taxonomy overview, species lists).

• Key features: paddle tail, compressed body, valved nostrils, venomous fangs.
• Typical habitats: coral reefs, lagoons, estuaries, seagrass beds.
• Major threats: habitat loss, pollution, fisheries bycatch, climate change.