Sea snake

Sea snakes, also known as coral reef snakes, are special kinds of snakes that live in the ocean most or all of their lives. They are part of a group called elapids and belong to two smaller groups, Hydrophiinae and Laticaudinae. Many of these snakes live only in saltwater, but some sea kraits can live in freshwater, too. In total, there are 69 different kinds of sea snakes spread across seven groups.

Most sea snakes have venom, but one group, called Emydocephalus, does not because they mostly eat fish eggs. These snakes have special bodies that help them swim, like flat tails and long, thin shapes that look like eels. Even though they look like fish, they cannot breathe underwater like fish do and must come up to the surface to breathe air. Sea snakes live in warm waters from the Indian Ocean to the Pacific Ocean and are closely related to some venomous snakes that live on land in Australia. Some sea snakes have very strong venom, but many are gentle and only bite when bothered.

Description

Most adult sea snakes grow to be between 120 and 150 cm (4 and 5 ft) long. The largest, Hydrophis spiralis, can reach up to 3 m (10 ft). They have small eyes with round pupils and nostrils on top of their heads. Their skulls are similar to land snakes, but they have short fangs and extra teeth.

Most sea snakes live only in the water and have special features that help them swim. They have paddle-like tails and bodies that are flattened on the sides, especially the ones that live far out at sea. Because of this, they cannot move well on land, but they do not need to leave the water. The only sea snakes that can move on land are called sea kraits, Laticauda. They have special scales on their bellies that help them grip the ground.

Sea snakes have special ways to breathe and manage salt in their bodies. They can breathe through the top of their skin, which helps them stay underwater longer. They also have special glands under their tongues that help remove extra salt from their bodies.

Sea snakes have different kinds of scales. Some have smooth scales, while others have spiny or warty scales. The scales help protect them, especially when they swim near sharp coral reefs.

Sensory abilities

Sea snakes and sea kraits live in water, where vision, hearing, and smelling are different than on land. Because water changes how we see, smell, and hear, these snakes might have special ways to sense their world.

We don’t know much about how sea snakes see, but studies show they have special cells in their eyes that help them see. Even though their eyes lack some parts that land snakes have, they might still sense light in other ways. Sea snakes may also use vibrations in the water and smells to find food and mates. Some sea snakes have tiny sensors on their heads that can feel movements in the water, like when a fish swims nearby. One kind of sea snake can even sense light with special cells on its tail, helping it hide in coral during the day. Scientists are still studying whether sea snakes can sense other things, like electric fields or pressure changes, but they haven’t confirmed this yet.

Distribution and habitat

Sea snakes live mostly in warm tropical waters of the Indian Ocean and the western Pacific Ocean, with a few species found in Oceania. One species, Pelamis platurus, has the widest range of any reptile except some sea turtles. It lives from the east coast of Africa, from Djibouti to Cape Town, across the Indian Ocean and Pacific, as far south as New Zealand's northern coast, and along the western coast of the Americas from Peru to the Gulf of California.

Sea snakes are not found in the Atlantic Ocean. They do not live in the Red Sea because of its higher salt levels, so they cannot cross through the Suez Canal. They also do not live in the Caribbean because of lower salt levels, even though the Panama Canal could allow them to move there.

Although they are adapted to water, most sea snakes prefer shallow waters near land, around islands, and in sheltered areas. They sometimes swim up rivers and have been seen far from the sea. Some live in mangrove swamps, and a few species live in freshwater lakes, like Hydrophis semperi in Lake Taal in the Philippines and Laticauda crockeri in Lake Tegano on Rennell Island in the Solomon Islands.

Behavior

Sea snakes are usually calm and not likely to bite. Some might bite if bothered, especially when trying to catch their food. Fishermen often handle them without trouble when the snakes get caught in nets.

When on land, sea snakes move in a clumsy way and may strike at things nearby, though they cannot coil up like land snakes.

These snakes are active during both day and night. They sometimes float on the water's surface to warm up in the sun and dive when something frightens them. They can swim very deep and stay underwater for a few hours.

Sometimes large groups of sea snakes are seen together. In 1932, many were spotted in the Strait of Malacca, near the coast of Malaysia, forming a long line in the water. The reason for such big gatherings is not known, but it may be related to their reproduction.

Ecology

Sea snakes eat small fish and sometimes young octopus. They are often seen with a special barnacle called the sea snake barnacle, which sticks to their skin.

Reproduction

Most sea snakes give birth to their babies in the water, where the babies live their whole lives. These babies can be quite big, sometimes almost half as long as their mothers. However, one group of sea snakes, called Laticauda, is different. These snakes lay their eggs on land instead of in the water.

Venom

Sea snakes are very poisonous, just like their relatives in the Elapidae family. However, they usually don't inject their venom when they bite, so it is rare for a person to be badly hurt by a sea snake bite. One type of sea snake, Hydrophis platurus, has venom that is stronger than any land snake in Costa Rica, but very few people have died from its bites.

When a sea snake does inject venom, the bite usually doesn't hurt and the person might not even notice it at first. The venom works very slowly, and symptoms can take from half an hour to several hours to appear. These symptoms include muscle pain, stiffness, and difficulty moving. In severe cases, the venom can cause paralysis, which is when the muscles stop working, starting with the muscles around the eyes and then moving to other parts of the body. This can be dangerous if it affects the muscles used for breathing.

The venom mostly affects muscles and the kidneys, rather than causing immediate paralysis like some other snake venoms.

Taxonomy

Sea snakes were once thought to be a special group all on their own, called Hydrophiidae. But scientists later found they have two subfamilies: Hydrophiinae, the true sea snakes, and Laticaudinae, the sea kraits. There are six groups of true sea snakes with 64 different types, and one group of sea kraits with eight types.

As scientists learned more, they realized sea snakes are closely related to other snake families. Now, most scientists say sea snakes belong to the elapid family, split into the Hydrophiinae subfamily and sometimes the Laticaudinae subfamily. The Hydrophiinae subfamily also includes land snakes from Australia and Asia.

Molecular studies

Studies using molecules show that three special groups of semiaquatic snakes — Ephalophis, Parahydrophis, and Hydrelaps — are some of the earliest to split off from other sea snakes.

Captivity

Sea snakes can be hard to keep as pets. They often feel nervous and don't like to eat, usually hiding in dark corners of their tanks. Even many years ago, people found them tricky to care for. Some places, like special water displays in Japan, have shown certain kinds of sea snakes, but it's not easy. Not all sea snakes can be kept because some need very special food. Some also don't like being handled or taken out of the water.

Certain sea snakes, like the ringed sea snake, can do okay in captivity if they are given fish and eels to eat. Another type, Hydrophis platurus, has done very well, even eating small fish such as goldfish. To keep them safe, their tanks should have rounded edges so they don't hurt themselves.

Conservation status

Most sea snakes are not listed for special protection. One species, Laticauda crockeri, is considered at risk. Some species of Aipysurus are also at higher risk. The Timor species A. fuscus is known to be in danger, and two others found in seas north of Australia, the leaf-scaled A. foliosquama and short-nosed A. apraefrontalis, are listed as in very serious danger according to the IUCN Red List of Threatened Species.