Sea Snakes Evolving to Survive Polluted Oceans

Sea snakes may be a new environmental canary in the coal mine, as one species has been steadily darkening in response to higher levels of water pollution off the coast of Australia. Unlike the bleached white coral reefs resulting from CO2-driven ocean acidification, these snakes are not changing color due to damage from pollutants, although pollutants are, indirectly, the source of the change. The higher levels of melanin are actually an evolutionary response to help the snakes adapt to the polluted waters, according to a recent study published in Current Biology.

Surprisingly, this isn’t even the first time this has happened. It’s called industrial melanism, and a famous example of this particular brand of industrial revolution turned microevolution is in the change in Britain’s peppered moths, seen below.


Photo credit: Thinkstock

You’ll notice that there’s some variation in the coloring of these moths. Indeed, the white moths with black specks do look as if they have been covered in black pepper. But there are black moths with white specks which might be more appropriately named “salted moths.”

Actually, this variation is natural, but the mostly white moths were more prevalent centuries ago, when the common name for the species was first given. They’re still relatively easy to find in parts of the countryside, but near London, the mostly white moths are rare. If you have two minutes, there’s a fun video that explains why.

The short answer: air pollution, particularly soot, darkened trees near urban centers as Britain industrialized. The white- or grey-barked trees became darkened with soot, and the black moths became better adapted to this new environment, as they were harder for predators to see against a dark background. The once-rare dark phenotype came to dominate as they were better suited to surviving in an environment affected by industrial pollution.

So, this recent study has discovered that turtle-headed seasnakes are markedly darker in waters near human industry and which have higher levels of pollutants. Are the snakes just trying to blend in with their murky, toxic waters?

Actually, no. Camouflage is not actually a strategy employed by these snakes, which generally hide from their few predators in cracks and crevices, and can also, if cornered, defend themselves with their venomous bite. So to explain the higher prevalence of the darker phenotypes in those snakes dwelling in polluted waters (which are not, in fact, visibly darker to begin with), the study authors cite previous work on urban-dwelling birds, of various species.


Photo credit: Thinkstock

According to previous research, melanin, the naturally-produced pigment that makes biological tissues darker, that is, more absorptive of light, also serves an additional, unexpected function. It turns out to be good at binding toxic trace elements that would otherwise poison the birds. Darker birds survive better, because they are able to shed feathers that have absorbed much of the pollutants that would otherwise have been absorbed into the birds’ bodies. That makes it difficult to watch a flock of dark grey pigeons in the concrete jungle without imagining the polluted air they have adapted to and which we are swimming in ourselves.

Likewise, the snakes, which are producing higher levels of melanin to shield themselves from industrial toxins signal that our water is likewise becoming increasingly polluted. Separate from the previously-mentioned ocean acidification, and the sea of plastic, we still have good old-fashioned heavy metals and other industrial by-products, of the sort human industry has been producing for centuries. The snakes absorb larger quantities of toxic industrial byproducts in their highly-melanized scales, shedding their skin regularly and leaving much of the poison behind.

The creativity in nature is a remarkable thing. Unfortunately, human beings, and many other species can’t do what these birds and snakes are able to. Hopefully, before our land, skies, and waterways become too toxic save for a few pollution-adapted, poison-shedding species, we we can reverse the trend and start cleaning up our own mess, for the sake of other species and our own.

Photo credit: Aloaiza


Margie F
Margie FOURIE15 days ago

We will all have to change, or face the consequences.

Pat P
Pat P23 days ago

Pollution is bad enough, but when there are no environmental protections--it is much worse. This is the sad fate of the U.S. , if the citizens don't get angry and do something to prevent the negative change. The present POTUS, EPA (led by Pruitt) and GOP intend to gradually (but not very) get rid of ALL environmental regulations, as well as the organization, itself. The EPA was started by Republican Nixon, but the modern political party (backed by extremist billionaires) doesn't care about the health of our planet--only money.

W. C
W. C28 days ago

Thank you for the information.

Carl R
Carl R29 days ago


Sherri S
Sherri Sabout a month ago

"The creativity of nature is a remarkable thing." Yes, it is remarkable, but so sad that species are forced to evolve due to the negligence of mankind.

Carl R
Carl Rabout a month ago


Ruth C
Ruth Cabout a month ago

Humans are to blame for all the horrible things that are going on in the world!

Tanya W
Tanya Wabout a month ago


Angeles Madrazo
Angeles Mabout a month ago

It's time to start doing something, we can do it! Thank you

Marie P
Marie Pabout a month ago