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Ian Bell Raine Island, Queensland

  • Coastal
  • Wildlife & Environment

Turtle sex altered with temperature changes

Sea level rise and warmer temperatures are a big threat to marine turtles on the Great Barrier Reef.

Photo: Troy Mayne

Marine turtle expert Dr Ian Bell is concerned about the survival of Queensland's marine turtles. As a biologist with the Threatened Species Unit at the Queensland Department of Environment and Heritage Protection, he is working with marine turtles to understand how climate change may affect them.

The Climate Commission says the sea level has already risen by 0.21 metres and will continue to rise as the ocean becomes warmer. And rising sea levels put the prime nesting areas of turtles at risk of flooding, forcing turtles to nest in less than ideal habitats, such as rocky or muddy beaches.

Higher temperatures could also lead to only females being born.  Ian says if marine turtles are to survive, populations need to thrive in very large numbers. Currently for every 1,000 hatchlings born only one survives to adulthood.
Ian explains.

Personally, I am not overly optimistic about the future of some species of marine turtle, such as leatherbacks, hawksbills, olive ridelys and green turtles in the northern Great Barrier Reef.  They only have a limited capacity to cope with a number of threats, and this includes climate change.

What we are seeing at places like Raine Island, which is the main nesting site for the northern Great Barrier Reef green turtle population, is that nesting success is low, which means hatchling production is even lower. When we should be having hundreds of thousands of hatchlings running down the beach and entering the water every night, we are only seeing thousands. A contributor to this is nest flooding. Some turtles are laying their eggs in water. You see them digging their egg chamber with their hind flippers and they are dropping their eggs into the water, so their eggs are drowning.


Climate change is rolling towards us right now. So will the turtles be able to handle more flooding of their nests? Are we going to see prime nesting beaches disappear so turtles end up nesting in less than ideal habitat?


But it's not only nest flooding taking its toll on Raine Island nesting turtles.  Only about half of the eggs laid on Raine Island will result in a hatchling being born. The rest of the eggs are dying part-way through the incubation period – and we have no idea why this is happening.

Plus, increasingly warmer temperatures mean more female turtles will be produced. There is a pivotal temperature, which on Raine Island is about 29C. Eggs incubating above this temperature will result in female hatchlings whereas males are produced in lower temperatures. This is a fine balance, and increasingly warmer temperatures will result in only females being produced.

We are likely to see a lot of changes in our marine environment, from the impacts of climate change, including ocean acidification. This includes a loss of sea grass and a change from coral to algal reefs. Green turtles feed on seagrass, and seagrass is really susceptible to warmer sea temperatures. As we have seen over the past few years, seagrass can disappear in an instant and this is a real issue for turtles.