Researchers Offer Solution to Puzzle of Sea Snakes With Jet-Black Skin

There’s something odd about turtle-headed sea snakes.

It’s not their name, or that they give live birth instead of laying eggs, or that they paddle more than they slither. It’s their skin.

For years, researchers noticed that the aquatic snakes living in waters near human activity had jet-black skin, but most others, in more pristine waters, were speckled or banded.

“It’s always been a puzzle,” said Richard Shine, an evolutionary ecologist at the University of Sydney who has been studying sea snakes for decades.

But now, in a report published last week in Current Biology, Dr. Shine and his colleagues suggested that the varied coloration of sea snakes is probably an adaptation that helps them deal with pollution. It’s sort of like the moths in Europe that swapped speckled for black wings during the Industrial Revolution, evading hungry birds by blending in with coal dust. Only, rather than camouflage, black sea snake skin may act more like a pollution trap collecting heavy metals absorbed by the snakes and then cleaning them out as the skin is shed.

Near New Caledonia, a French archipelago in the southern Pacific Ocean, turtle-headed sea snakes swim around, gobbling up fish eggs from the bottoms of bays and lagoons. On these islands, tourists sunbathe on beaches, cars drive on roads and workers mine nickel in the mountains. When it rains, pipes and rivers carry runoff from these activities and dump it directly into the homes of sea snakes.