Sea snakes are a paradoxical creature; on the one hand, they have a reputation for being gentle beautiful creatures that people often interact with while diving, and they don’t create anywhere near the fearsome and terrifying reactions that most of their land counterparts do. At the same time, they are actually highly venomous; in fact, more so than most of their land based cousins. Yet, divers are happy to hover within a couple of meters of a sea snake, but would not go anywhere near as close to snakes on land. So welcome to the fascinating world of sea snakes.
These beautiful creatures are descended from their land living relatives; in fact, most sea snakes in the Indo-Pacific are related to Australian land snakes. Unlike pure aquatic animals, sea snakes breathe air and surface regularly to breathe; however, one unique adaptation they have to the aquatic realm is their ability to absorb oxygen through the skin surface. Experiments have shown that a sea snake can satisfy 25% of its body’s oxygen needs through the skin; this adaptation allows them to make much longer dives.
Another needed evolution is how sea snakes deal with salt: since they are originally land animals, they cannot tolerate the extreme highs of salt like other marine creatures; as a result, the have developed special glands under and around their tongue that allows them to eliminate the excess salt in their bodies.
The final evolution undertaken by sea snakes is in their scales; most land snakes have overlapping scales that are designed to protect their body against the constant abrasion of the ground. Sea snakes, on the other hand, do not need this abrasion protection. Instead, their scales are smooth and don’t overlap and are designed to be more hydrodynamic and to act as an armor against sharp corals.
Sea snakes live across the globe in warm temperate waters; like most reptiles, they do not like the cold. They can be found across the globe in all tropical water from the Caribbean to Australia and the east coast of Africa. Interestingly, for reasons not properly understood, the only bodies of water not inhabited by sea snakes are the Atlantic Ocean and the Mediterranean Sea, despite the fact that both having water warm enough to support sea snakes. This is especially surprising since it means that for some unknown reason, sea snakes are either unwilling or unable to cross the Panama Canal or the Suez canal respectively, unlike many other species who have completed this crossing.
Sea snakes, like their land cousins, are venomous; and although bites are rare, they do happen. Unlike land snakes, when sea snakes bite, they do not tend to inject large amounts of venom in comparison to land snakes. As a result of this minor envenomation, the initial bite is often painless and symptoms do not appear immediately. Despite the small volume of venom delivered per bite, bites by sea snakes are very dangerous due to the potency of the venom. If left untreated, death can occur 8 to 12 hours after a bite.
One of the most common myths you will hear about sea snakes is that because of their small fangs for venom delivery, they are unable to bite a diver except on the ear lobe and the area of skin between the thumb and index finger. This is a complete and utter fallacy. Most sea snakes are very docile and timid by nature, and fishermen in tropical waters are regularly seen handling them and uncoiling them and throwing them back in the sea. The snake’s lack of desire to bite and envenom is not to be confused with its lack of ability to bite. Sea snakes can bite and penetrate any exposed human skin, and since most are highly venomous, this can lead to fatalities – although most sea snakes would probably struggle to bite through a 5 mm wetsuit.