By Catherine Brahic (Image: Lucy Hawkes) (Image: Matthew Godfrey) (Image: Matthew Godfrey) Male loggerhead turtles could entirely disappear from the beaches of Florida – one of the most important nesting grounds in the US – if the temperatures there rise by 2°C, according to a new study. This gender imbalance means female turtles in Florida will be increasingly reliant on male turtles migrating from North Carolina, hundreds of miles up the Atlantic coast, in order to breed. And as the coast warms, the northern male turtle population will find it harder to meet such breeding demands, the researchers fear. The gender of marine turtle offspring is determined by the temperature at which the eggs are incubated: high temperatures lead to a higher proportion of females. In Florida, 90% of offspring are females, while in North Carolina, female turtles make up a more balanced 58% of the population. Brendan Godley at the University of Exeter, UK, and colleagues, analysed 26 years of data to see if fluctuations in temperatures had an influence on sex ratios of turtles in North Carolina. They found no significant trends, but when they put the data into computer models and simulated a rise in temperature – as predicted through global warming – the results were striking. A 2°C rise in temperature in the Cape Canaveral colony in Florida would entirely wipe out male offspring according to the models. It would take a 5°C rise to cause the same effect in Bald Head Island in North Carolina, at which stage the higher temperatures would already be causing more than 75% of deaths among the all hatchlings in Florida. “We are stunned by these results,” Godley says. “This is a major issue for nesting populations further south, in Florida, for example, where males are already in short supply.” Researchers believe that some males may already be travelling south from North Carolina to reproduce, bolstering the populations there. With a 2°C temperature rise, “males from northern populations might become essential” to Cape Canaveral, one of the most important nesting grounds in the US, says Godley. Godley has another cause for concern. Beaches on the eastern seaboard are degraded by the construction of new roads and houses. To replace the sand and “rejuvenate” the beaches, sand is dragged from the bottom of the sea in front of the beach or from nearby inlets. The sand that comes from the bottom of the sea is often much darker than usual beach sand and can cause beach temperatures to rise by 1°C to 2°C. “This might not seem like much, but in our situation, nest temperatures on natural beaches are around the pivotal temperature. A 1°C to 2°C increase can push sex ratios of hatchlings produced to close to 100%,” Godfrey told New Scientist. “In the face of climate change, it’s essential that we prioritise the protection of sites that produce males not only for local breeding success, but to help support potentially vulnerable populations further south,” says Godley. Journal reference: Global Change Biology (DOI: 10.1111/j.1365-2486.2006.01320.x) Climate Change – Want to know more about global warming – the science, impacts and political debate?