Sea snakes – or as my friend Bridget says “Snea Snakes”, are related to cobras (once placed in the same family Elapidae, but now the sea snakes are placed into the hydroelapidae). Similar to cobras, they have toxic venom, or rather most species have toxic venom.
The most toxin species appears to be the Faint-banded Sea Snake, Hydrophis belcheri, also known as Belcher’s sea snake. It can grow up to a meter in length. A more dangerous species is the Beaked Sea Snake, Enhydrina schistose, as its encountered more often by fisherman—the group most prominently bitten. Though the venom might be potent, deaths from sea snakes are unusual, probably due to their non-aggressive nature. Anti-venom is available and even when it wasn’t the death rate from sea snake bites were less than 10%.
In 2018 there was a death in Australia from a sea snake bite. This was the first death in the country for 80 years.
One group of sea snakes are the Kraits: The Kraits are less laterally flattened and thus appear to not be as well adapted to aquatic life as the other sea snake species. The Kraits are also not as closely related to the other sea snakes and are thought to have invaded the sea along a second evolutionary line from the other sea snakes. Besides being morphological distinct, the kraits lay eggs (they must venture onto land to do this) while the other sea snakes give birth to live young (ovoviviparous).
Giving birth to live young could be seen as a preadaptation, allowing those snakes so accoutered to more easily invade the sea. The late Stephen Gould wanted to call these adaptations (those that come about for a different reason that aid the organisms later in its evolutionary history) exaptations but that word doesn’t seem to have stuck.
Another adaptation that would appear necessary for life in the sea are salt glands. Sea snakes have salt glands which allow them to get rid of excess salt. For this reason, and others, for example they are sometimes observed far from shore and thus far from any apparent fresh water source, they were thought to drink sea-water. A series of observational studies have shown that that isn’t the case and they require freshwater to drink. This is the case even in the open water species mentioned in the first paragraph the Yellow-bellied Sea Snake.
Where does the sea snake find freshwater? It appears as though they drink from pools of freshwater that form at the surface due to rainfall. Freshwater is less dense than sea water and so it sits on top. It also takes time for the waters to mix.
These areas of freshwater, Lillywhite refers to them as lenses in his paper below, must not exist during dry periods and there are areas of sea snake distribution that go through long periods of drought. During these dry periods snakes lose mass, water weight. During long drought periods they are not in good shape. Life as a sea snake seems tough. I’m not sure why they have such a mild temperament, I’d be pissed and would be envenomating everything that gets in my way. FYI, I’m not sure envenomating is a word.
Here is a quick breakdown of the genera of sea snakes:
Aipysurus – olive sea snakes - 7 species.
Emydocephalus – turtlehead sea snakes -3 species.
Fangs but no other teeth. No venom, they eat fish eggs.
Enhydrina – beaked sea snakes – 2 species.
Hydrophis – The largest genera 36 or so species.
Parahydrophis – mangrove snake – 1 species.
Thalassophis – anamolous sea snake – 1 species.
Laticauda – sea kraits – 5 species.
Sea snakes are probably not the best pets, though venomous snakes do seem to collect collectors.
Does anyone keep these as pets?? I'm not suggesting you do so, I just wonder how many knuckleheads are out there :-)
Readings:
If you’re interested in sea snakes, look up the work of this Lillywhite guy (University of Florida Gainesville), just a small array of his work is listed below.
Lillywhite HB, Babonis LS, Sheehy CM III, Tu M-C. 2008. Sea snakes (Laticauda spp.) require fresh drinking water: Implication for the distribution and persistence of populations. Physiological and Biochemical Zoology81: 785–796.
Lillywhite, HB, Sheehy, CM III, Heatwole, H., Brischoux, F., and Steadman,
D. W. 2018. Why are there no sea snakes in the Atlantic? BioScience 68: 15–24.
Lillywhite HB, Sheehy CM, III, Sandfoss MR, Crowe-Riddell J, Grech A. 2019. Drinking by sea snakes from oceanic freshwater lenses at first rainfall ending seasonal drought. PLoS ONE 14(2): e0212099.
Reid, HA. 1975. Epidemiology of sea-snake bites. Journal of Tropical Medicine and Hygiene 78(5): 106-13.