Sea snakes divide into two groups with different histories. The true sea snakes of the subfamily Hydrophiinae are fully aquatic, bear live young at sea and are close to helpless on land. Sea kraits of the genus Laticauda retained broad belly scales and can crawl properly, so they occupy both worlds.
A typical cycle is a foraging trip on the reef, where the snake probes crevices for eels, followed by a return to shore. On land it digests, sheds, and crucially drinks. Marine reptiles cannot make fresh water from seawater efficiently, and sea kraits depend on rain-fed pools and freshwater lenses on islands. Eggs are laid ashore, unlike in the live-bearing true sea snakes.
Sea kraits are highly venomous but extremely reluctant to bite, and snorkellers and fishers routinely handle them without incident. That tolerance should not be mistaken for harmlessness; envenomation is rare rather than impossible, and the fresh water requirement makes island populations more vulnerable to development than their reef habitat alone would suggest.