Sea Snakes : The sea snake is primarily found in the northern waters of Australia. There are approximately 31 different species of sea snake. All of them are dangerous to humans, but relatively few of these bites cause any significant injury because the sea snake fangs are extremely tiny, only 2-4 mm. in length. They do contain neurotoxins, however, but most often cannot penetrate the wetsuit worn by a diver. Deaths that have been documented occurred among fishermen who ran into their nests. Sea snakes bear their young on shore, and spend the remainder of their lives in the ocean looking for food, sea fish and eel. They are very shy and not aggressive by nature.
After being bitten, side effects generally do not appear for 20-30 minutes, at which point severe pain is experienced in the affected limb. Droopy eyelids, respiratory weakness and muscle pain can occur. There is anti-venom available for sea snakes ; however, if unavailable, the anti-venom for the tiger snake may be used. An adult sea snake may carry enough venom to kill approximately three adult people. Its primary neurotoxin can cause peripheral paralysis. The sea snake venom is approximately two times more potent than the land snake venom, in comparing rattlesnakes, copperheads and water moccasins. Although more lethal, there is less chances of being bitten given the small size of the fangs and less aggressive nature of the snake.
Types of sea snakes : There are five major groups of sea snakes.
1) Hydrophiids : 'true' sea snakes
The largest group of sea snakes, the hydrophiids or 'true' sea snakes, evolved from Australian terrestrial elapids that returned to the marine environment around 30 million years ago.
Hydrophiid sea snakes have the same toxic venom and envenomation apparatus (they are proteroglyphs meaning they have fixed front fangs) as their terrestrial ancestors.
Hydrophiid sea snakes have exploited the viviparity that exists in some of their terrestrial ancestors, and have thus freed themselves entirely from the need to return to land to breed.
There are 54 species of hydrophiid sea snakes.
2) Laticaudids - sea kraits
The laticaudids or sea kraits comprise five species, four of which are marine. They are strongly banded and commonly seen in large numbers on beaches in south east Asia and some Pacific Islands.
Sea kraits have also evolved from terrestrial elapids and are proteroglyphs and have highly toxic venom. However they are very placid and unlikely to bite unless provoked.
Sea kraits are the only group of sea snakes that are oviparous (egg laying) and must return to land to breed.
3) Acrochordids - file snakes
The acrochordids or file snakes comprise three species. One species is fully marine while the others live in estuaries and freshwater habitats.
File snakes are not venomous and they give birth to live young.
4) Homalopsids - mangrove snakes
Homalopsids are colubrids that are confined almost entirely to estuarine environments.
There are nine species of aquatic homalopsids that are found primarily in tropical Asian waters and northern Australian waters. Only three species are fully marine.
Homalopsids are venomous but they are rear-fanged.
5)Natricids - salt marsh snakes
Natricids are colubrids that are confined almost entirely to salt marsh environments.
The three species of marine natricids are confined to temperate and subtropical north America and are not venomous. It is thought that these natricids might be in the early stages of evolving marine adaptations.
i) Banded sea snake : Laticauda colubrina
Description : Smooth-scaled snake that is a pale shade of blue with black bands. Its oarlike tail provides propulsion in swimming.
Characteristics : Most active at night, swimming close to shore and at times entering tide pools. Its venom is a very strong neurotoxin. Its victims are usually fishermen who untangle these deadly snakes from large fish nets.
Habitat : Common in all oceans, absent in the Atlantic Ocean.
Length : Average 75 centimeters, maximum 1.2 meters.
Distribution : Coastal waters of New Guinea, Pacific islands, the Philippines, Southeast Asia, Sri Lanka, and Japan.
ii) Yellow-bellied sea snake : Pelamis platurus
Description : Upper part of body is black or dark brown and lower part is bright yellow.
Characteristics : A highly venomous snake belonging to the cobra family. This snake is truly of the pelagic species--it never leaves the water to come to shore. It has an oarlike tail to aid its swimming. This species is quick to defend itself. Sea snakes do not really strike, but deliberately turn and bite if molested. A small amount of their neurotoxic venom can cause death.
Habitat : Found in all oceans except the Atlantic Ocean.
Length : Average 0.7 meter, maximum 1.1 meters.
Distribution : Throughout the Pacific Ocean from many of the Pacific islands to Hawaii and to the coast of Costa Rica and Panama.
Species diversity and distribution :
There are approximately 70 species of sea snakes living in our modern oceans. They account for 86% of marine reptile species alive today. Other marine reptiles include 7 species of sea turtles, the salt water crocodile and the marine iguana.
Sea snakes are cold blooded reptiles and are found primarily in warm tropical waters of the Indo-West Pacific. They are not found in the Atlantic Ocean or Caribbean Sea.
The area of highest species diversity is between Singapore and Borneo, with 27 species. Australia.s coastal waters also has a high species diversity that ranges between 17 to 21 species, and the Great Barrier Reef has 14 species of sea snakes. Although sea snakes need warm tropical waters to survive, they are occasionally blown south by storms and have been recorded in Sydney harbour.
Marine fouling and shedding of skin :
All snakes shed their skins. Sea snakes shed every two to six weeks, which is more frequently than land snakes and more often than needed for growth alone. The process involves rubbing the lips against coral or other hard substrate to loosen the skin. The snake then catches the skin against something to anchor it and crawls forward leaving the skin turned inside out behind it.
Skin shedding allows sea snakes to rid themselves of fouling marine organisms such as algae, barnacles and bryozoans. Otherwise they would be covered with fouling organsims like the hull of a boat that needs to be cleaned and this would interfere with the snakes ability to swim efficiently and may also cause disease.
Olive sea snake starting to shed its skin. The old skin is turned inside out along the snakes body behind the head.
Courtship, mating and reproduction :
Like all snakes and lizards, male sea snakes have two penises. They are called hemipenes, but each is an autonomous independently functioning penis and only one is used during mating. Mating takes place for long periods and sea snakes must surface for air during that time. The female controls breathing and as she swims to the surface the male is pulled along attached via the hemipenis. At the surface the male needs to gulp for air or he has to wait til the next time the female comes up the the surface to breathe. Males are unable to disengage until mating is finished.
In species where courtship has been studied, eg olive and turtlehead sea snakes, one or more males follow the female very closely and occasionally prod the head and neck of females.
All sea snakes except the latidcaudids give birth to live young after gestation periods that range from four to eleven months, depending on the species. Most species reproduce every year. The timing of the reproductive cycle varies enomously between species and also differs between geographical locations for the same species.
Young are born underwater and must be independent immediately to swim to the surface to breathe. There is no parental care. In some species look quite different to the adults eg juvenile olive sea snake are strongly banded while the adults are not.