Science

Metal pollution may be skewing the sex ratio of sea turtles

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A green sea turtle hatchling on Heron Island, Australia

Genevieve Vallee / Alamy

Chemical pollution could be skewing the sex ratio of sea turtles by making more eggs hatch as females, putting the species at risk of extinction.

Sea turtles are one of many reptiles whose sex depends on temperature. In warmer nests, females are more likely to hatch, while cooler nests favour male turtles. As global temperatures continue to rise, more and more sea turtle populations are becoming overwhelmingly female – a trend that could lead to their disappearance.

In one population of green sea turtles (Chelonia mydas) in the northern Great Barrier Reef, 99 per cent of hatchlings have been females in the past few years.

Now, Arthur Barraza at Griffith University in Australia and his colleagues have found that pollution on beaches may also be driving the sex bias in green sea turtles.

The team collected 17 clutches of eggs shortly after they were laid on Heron Island, a small sand island on the Great Barrier Reef, and reburied them near sensors that monitored the temperature of the sand once an hour. After the eggs hatched, the researchers euthanised the turtles from 16 of the clutches and examined their sex organs to find out their sex.

They then dissected the turtles’ livers to look at whether pollution had got into the hatchlings’ bodies.

Of the 16 sampled clutches, the team found that 11 had more females than predicted from temperature alone, three had more males than expected and two matched the expected sex ratio.

The hatchlings in the clutches with more females than were predicted had higher levels of cobalt, lead and antimony in their bodies, while those with more males had lower levels of the heavy metals.

Most of these metals are waste from industrial processes, says Barraza. The metals can bind to oestrogen receptors, which may trigger the development of female hatchlings.

However, the findings only show a correlation and can’t prove that metal pollution is altering the sex of turtle hatchlings. Nevertheless, Barraza hopes the results could inform conservation efforts. “Human pollution affects turtles and wildlife in ways that maybe people do not expect,” he says.

“These data provide a disturbing insight to the more subtle effects of human-induced environmental contamination in a species with populations already heavily skewed in favour of females and climatic influence,” says Arthur Georges at the University of Canberra, Australia.

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