Warming seas are likely to threaten sea turtle survival even as the animals lay their eggs at cooler times of the year to adapt to climate change, new research suggests.
Modeling by Australian scientists at Deakin University has found that sea turtles are unlikely to be able to change their nesting behavior enough to mitigate the effects of higher sea surface temperatures.
Analyzing 58 breeding grounds worldwide spanning all seven species of sea turtles, the researchers suggest that if the reptiles laid their eggs earlier to avoid warmer beaches, each shift would represent, at best, 55% of a 1.5° rise in sea temperature. C would decrease.
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The sex ratio of turtle hatchlings is closely determined by the temperature of the nest in which the eggs are hatched, with warmer nests yielding more females. Higher temperatures have also been associated with lower hatchling success rates.
In a “doomsday scenario,” said study co-author Prof. Graeme Hays, “only females could be produced from certain populations, which would obviously lead to the population’s extinction.”
Previous research has linked warmer seas to predominantly female green sea turtle populations in parts of the Great Barrier Reef. A 2018 study found that 99.1% of young turtles were females, originating from nesting beaches in the north of the reef.
Hays stressed that the new research was not “all doom and gloom,” but highlighted the potential need for conservation strategies to cool temperatures on breeding beaches.
“There’s a lot of good news around the world with sea turtles,” he said. “Populations are increasing in a number of locations around the world; preservation really works successfully.
“With climate-warming feminization [research]what we’re trying to do now is get the information so we can avoid problems later… [so] if turtles need help along the way, we are not caught off guard.”
Sea turtles tend to nest in the area where they hatched, a behavior known as birth control. It means, the researchers suggest, that they “cannot easily adjust their range to warming temperatures.”
The study, published in the journal Royal Society Open Science, assumed an expected 1.5°C increase in sea temperature, “as this warming is very likely to occur before the end of the century”.
It was also based on existing research showing that warming temperatures may lead to earlier nesting. A study of loggerhead turtles in the Mediterranean had previously found that in extreme cases, turtles laid eggs about 18 days earlier when the water warmed by 1°C.
Christine Madden Hof, the global leader of sea turtle conservation at the World Wide Fund for Nature (WWF), said: “We need more data to understand how the different species of sea turtles in different places around the world will fare in the face of climate change.
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“If we know that those population groups are not doing well, we really have to think seriously about scientifically substantiated [interventions].”
WWF is participating in trials that have successfully used seawater and freshwater to artificially cool turtle nests.
Increasing shade on beaches using marquees or planting vegetation has also been proposed as an approach that could improve sex ratios. It would take care to make sure nesting habitats weren’t disturbed, Hays said.
“You play god when you make an intervention,” said Hof. “It could be that a very cool rainy year or several years produce enough males to maintain the population, so we don’t want to intervene if it’s not necessary.”
WWF is also currently investigating the minimum number of male turtles needed to maintain populations.
Of the seven living sea turtle species, six are on the International Union for Conservation of Nature Red List of Threatened Species.