Eggs submerged under seawater are less likely to hatch, study at world’s largest green turtle nesting site on the Great Barrier Reef shows
Wednesday 22 July 2015
The world’s largest aggregation site for nesting green turtles on Raine Island, the Great Barrier Reef, Queensland. Photograph: Great Barrier Reef Marine Park Authority/AAP
Rising sea levels could decimate sea turtle nesting sites around the world, scientists have warned, with the largest rookery site for green turtles increasingly at risk from being swamped by seawater.
Researchers have tested the impact of seawater upon turtle eggs in an attempt to find out why so few hatchlings were emerging on Raine Island, on the fringes of the Great Barrier Reef.
Raine Island is a remote coral cay that acts as the world’s largest nesting site for green turtles – as many as 100,000 female turtles can lay eggs in the sand each summer.
Scientists, concerned that only 10% of eggs are producing turtles, compared to 90% in other parts of the world, tested the effect of seawater upon the eggs.
They found that eggs submerged in seawater for up to six hours had far less chance of hatching, due to the need for embryos to gather oxygen from the surrounding environment to avoid suffocating.
Given that low-lying Raine Island is regularly hit by king tides and storms, the researchers warned that rising sea levels would prove highly problematic for turtle species on the island and around the world.
“If we went to another turtle population and did the same experiment, I think we’d find something similar,” said Dr David Pike, a scientist at James Cook University, who led the research.
“A big concern worldwide will be trying to predict how sea level rises will impact sea turtle populations. It will take 20 to 30 years for us to realise that we don’t have many adult turtles anymore, because the current hatchlings aren’t making it.”
Pike said that should Australia experience a predicted sea level rise of 50cm over the next 100 years, due to melting ice caps and thermal expansion of the ocean via global warming, Raine Island “could be washed away.”
“That would be very concerning and would have an impact on green turtle populations across the region,” he said. “It also suggests it could happen elsewhere.”
Green turtles lay about 100 eggs on Raine Island at any one time, and will repeat the process four or five times during the summer. Female hatchlings that survive will return to the island as adults to lay eggs, battling for space with thousands of other turtles.
Any drop in hatching rates is significant given how few turtles survive to maturity. Just one in every 1,000 hatchlings survives once they enter the water, due to the dangers they face from ocean predators.
Green turtles are listed internationally as endangered. They are one of seven sea turtle species, the others being the loggerhead, the leatherback, the hawksbill, the Kemp’s ridley, the Olive ridley and the flatback.