Amphibious sea snakes – torn in between

When I attended the International Wildlife Management Congress (5th IWMC) in Sapporo Japan, I was blown away with a very interesting group of sea snakes: the amphibious sea snakes (Laticaudinae), also known as sea kraits. They possess traits of both land and sea snakes. They are kind of torn between living on land or in the ocean. Their evolution has led to characteristics that enable them to live in both environments, at least for certain periods at a time. But these multiple skills come with a trade-off. For example the locomotion ability in aquatic environments may reduce their terrestrial locomotor ability and vice versa. Even though terrestrial crawling and aquatic swimming are superficially similar activities in snakes, they need different substrates to produce the motion. In general sea kraits move over twice as fast in water than on land.

The ability to move on land is based on both their ventral scales, which are wide just as with land snakes, and their poorly developed tail fins. Sea kraits also use land as their freshwater source. Even though they have a salt gland to excrete the excess salt, they also have to drink freshwater to obtain a proper water balance within their bodies. The freshwater resources that sea kraits use are rainwater, estuaries and sea springs. Estuaries are used by all species, not just to drink freshwater, but also to hide.

The reproduction of amphibious sea snakes differs from true sea snakes (Hydrophinae). Firstly, they are oviparous, whereas true sea snakes are viviparous. Viviparous means that snakes give birth to live young. Oviparous on the contrary means the animal lays eggs and the offspring hatch from them. Sea kraits return to land to mate and lay eggs. The eggs are laid in nests fulfilling certain specific condition.

Sea kraits have lungs for breathing. They therefore need to surface every 15 minutes on average to breathe. The breaking of the surface may take only a split second while a sea krait takes a breath of air and dives again. Most of their time they spend at sea in shallow tropical reefs, which are threatened in several ways. Agricultural and urban runoff, in addition to both organic and inorganic pollution are one of the main threats to shoreline tropical reefs. Many sea krait species are considered vulnerable or nearly threatened. Hopefully we will be able to conserve these interesting and mesmerizing creatures of the oceans before it’s too late.