Sea snakes living near humans turn black due to pollution

Experts say the blacker skin of urban sea snakes living on coral reefs in the Indo-Pacific allows them to better bind and rid their bodies of contaminants each time they shed their skins.

Sea snakes lose their stripes the nearer they live to humans, and it may be because of pollution.

Researchers studying turtle-headed sea snakes living on coral reefs in the Indo-Pacific noticed something unusual about the serpents' colour patterns.

Sea snakes living in more pristine parts of the reef were decorated with black-and-white bands or blotches.

But those in places with regular human activity, such as near the city, were black.

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Sea snakes lose their stripes the nearer they live to man, and because of pollution, suggests a new study. Seas nakes living in more pristine parts of the reef were decorated with black-and-white bands or blotches (pictured)

Sea snakes lose their stripes the nearer they live to man, and because of pollution, suggests a new study. Seas nakes living in more pristine parts of the reef were decorated with black-and-white bands or blotches (pictured)

THE COLOUR CHANGE

The researchers measured trace elements of pollutants in the shed skins of sea snakes from urban-industrial compared to other areas and in dark versus light skin.

As predicted, concentrations of pollutants were higher in snakes from urban-industrial areas.

Pollutant concentrations were also higher in darker than in paler skin.

The researchers further found that darker snakes shed their skins more often.

As a result, it appears that sea snakes whose skin is more heavily pigmented with melanin have an advantage over their lighter relatives in polluted areas.

The blacker skin of urban sea snakes allows them to more effectively bind and rid their bodies of contaminants, including arsenic and zinc, each time they shed their skins. 

The colour changes are the result of an adaptation to differences in the snakes' exposure to pollution, according to the international team of researchers.

The blacker skin of urban sea snakes allows them to more effectively bind and rid their bodies of contaminants, including arsenic and zinc, each time they shed their skins.

The findings add sea snakes to a growing list of species that show industrial melanism, a greater prevalence of dark-coloured varieties in industrial areas.

Study coauthor Professor Rick Shine, from the University of Sydney, said: 'The animals I study continue to astonish me.

'I think it's remarkable to find industrial melanism in organisms as different as moths and sea snakes.'

The researchers got the idea that blacker skin might be related to pollutant exposure after learning that the darker feathers of urban pigeons in Paris store more zinc than lighter feathers.

Seasnakes living in places with regular human activity, such as near the city, were found to be black (pictured) by scientists

Seasnakes living in places with regular human activity, such as near the city, were found to be black (pictured) by scientists

They wondered whether a similar thing might be happening in the sea snakes, which they had already noticed changed colour around areas of human activity.

To find out, the researchers measured trace elements of pollutants in the shed skins of sea snakes from urban-industrial compared to other areas and in dark versus light skin.

As predicted, concentrations of pollutants were higher in snakes from urban-industrial areas.

Pollutant concentrations were also higher in darker than in paler skin.

The researchers further found that darker snakes shed their skins more often.

As a result, it appears that sea snakes whose skin is more heavily pigmented with melanin have an advantage over their lighter relatives in polluted areas.

Professor Shine said that the findings are another example of rapid adaptive evolutionary change in action, but added that the adaptation is a reminder of the effect humans can have on wildlife. 

He said: 'Even on an apparently pristine coral reef, human activities can pose very real problems for the animals that live there.'

The blacker skin of urban sea snakes allows them to more effectively bind and rid their bodies of contaminants, including arsenic and zinc, each time they shed their skins

The blacker skin of urban sea snakes allows them to more effectively bind and rid their bodies of contaminants, including arsenic and zinc, each time they shed their skins