Pollution Is Causing More and More Turtle Embryos to Develop Into Females, Threatening Species' Existence!

Sea turtles’ sex is temperature-dependent — as mercury rises, more and more embryos develop into females. In the northern Great Barrier Reef, the scales have already tipped dramatically, with hundreds of females emerging for every male.

Now, researchers have found that contaminants from human activities may also be influencing the sex ratio of developing green sea turtles, intensifying the existing gender bias and pushing these ancient mariners perilously close to the edge.

When contaminants mimic hormones

Researchers took to Heron Island, a small coral sand cay in the southern Great Barrier Reef where between 200 and 1,800 females come to nest every year. The sex ratio at this long-term turtle monitoring site is currently more balanced than nearer the equator, with approximately two to three females hatching for every male.

For this study, approved by the animal ethics committee of the University of Queensland and the Queensland Parks and Wildlife Services, the researchers meticulously monitored temperature variations inside turtle nests and at the beach surface. They also euthanised some hatchlings for sex determination and examination of livers for contaminant measurement.

Their focus encompassed 18 metals, including chromium, antimony and barium, along with organic contaminants like polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs).

These compounds are accumulated by female turtles at their foraging sites, then absorbed by the eggs developing within them, and finally sequestered in the liver of the embryos, where they can stay for years after hatching. But more importantly, they are known to act as 'xenoestrogens' that mimic the receptors for female sex hormones.

These results led the researchers to conclude that these contaminants mimic the function of the hormone estrogen, steering developmental pathways towards females.

“As the sex ratio gets closer to 100% females, it will get harder and harder for adult female turtles to find a mate. This becomes especially important as climate change will continue to make nesting beaches warmer and more female-biased,” said Dr Arthur Barraza, a researcher at the Australian Rivers Institute at Griffith University and the first author of the study.

Now, unravelling the specific compounds influencing hatchling sex ratios becomes imperative for crafting strategies to shield sea turtle populations from the feminising effects of pollutants. As these ancient mariners navigate the challenges of their precarious existence, a scientific approach is paramount to rid our oceans of pollutants and ensure the turtles’ enduring presence in our oceans.

T​his study was published in the journal Frontiers in Marine Science and can be accessed here.

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