Under a moonlit sky, turtle hatchlings ​emerge from the sand on Türkiye's Mediterranean coast and scramble towards the sea, taking part in an ancient natural cycle that scientists say is increasingly being shaped by climate change.

Throughout the night, sea turtle biologist ⁠Yakup Kaska and his team of volunteers monitor activity in the nests. Pyramid-shaped ⁠cages protect the eggs buried in the sand from foxes that roam the 4-kilometer (2.5-mile) Iztuzu sandbar, a tourist beach by day and haven for turtle conservation by night.

The loggerhead turtle, which nests on shores across the Mediterranean, is the mascot of COP31, ​the annual U.N. climate summit that Türkiye hosts next month. Marine conservation will be a key focus of ​the ⁠gathering along the coast in Antalya.

Researchers say the turtle illustrates how climate change is altering ecosystems in the Mediterranean, which has experienced a long-term warming trend since the early 1980s.

Turtles as climate barometer

A Reuters analysis showed European waters had their hottest summer months on record with severe consequences for some coastal communities. Researchers say climate change is also steadily warming nesting beaches across the Mediterranean.

The sex of turtle hatchlings is determined by nest temperature. Warming sands produce more females.

"Sea turtles provide us with a very rapid warning system," said Üsküdar University ecology lecturer Ayfer Şirin, who has carried out extensive research on loggerheads. She said they reflect environmental changes affecting coastal and marine ecosystems because they depend on both land and sea.

In a five-year doctoral study at Pamukkale University, Şirin found that warming temperatures were linked to earlier nesting, shorter incubation periods and a predominance of females.

The study at Patara beach estimated that on average some 70% of loggerhead hatchlings were female and concluded that behavioral adjustments alone may not be enough ⁠to ⁠offset the effects of climate change.

Nest temperatures at Iztuzu rose by nearly 1 degree Celsius (1.8 degrees Fahrenheit) over the past 20 years, Kaska said, adding that broader analysis suggested females accounted for as many as 80%-90% of hatchlings in many sea turtle populations.

Scientists say there is a risk that continued warming may eventually produce too few males to support successful reproduction. Another hazard is that nest temperatures above 30 degrees Celsius (86 degrees Fahrenheit) increase the risk of embryo mortality, Şirin said.

According to the Marine Turtle Specialist Group, loggerheads are classified as vulnerable globally. Those in the Mediterranean are listed among those of least concern, reflecting conservation gains, but scientists say climate change is creating new pressures.

Habitats, cooperation

The turtles' migratory lifestyle illustrates the need for cross-border cooperation at COP31, Kaska said.

"They might be nesting in Türkiye, but they are feeding in Tunisia or they ⁠are feeding in the Adriatic and so on," he said, calling on countries to collaborate to protect Mediterranean biodiversity.

COP31 President Murat Kurum, Türkiye's environment minister, told an Ocean and Seas conference last month: "Protecting the oceans is a responsibility we all share. We call on every party to turn that responsibility into bold, concrete action: restoring ecosystems and building resilience."

Türkiye ​has set a goal of reaching net-zero greenhouse gas emissions by 2053 and has highlighted the expansion of renewable energy as a key element of ​its climate strategy.

Growing threats

Female loggerhead turtles typically return decades later to nest on the beaches where they hatched, but ecosystem changes mean some are nesting farther north, where they were previously uncommon, Kaska said.

However, Iztuzu remains a key location with about ⁠30,000 hatchlings entering the ‌sea each season ‌from hundreds of nests.

On the beach, volunteers monitor the hatchlings, using dim red lights to minimize ⁠disturbance as they navigate towards the waves. In the sea, the hatchlings face further threats, including ‌from fishing nets, boats and plastic waste.

"A sea turtle caught in a fishing net cannot come up for air and unfortunately dies by drowning," Şirin said.

A short walk from Iztuzu ​beach, injured turtles recover in large circular pools at ⁠the Dekamer rehabilitation center, where veterinarians treat injuries, including from boat propellers.

Plastic pollution is a particular concern. ⁠Kaska said 60% of turtles brought to the centre have at least five pieces of plastic in their digestive systems.

"Throwing a plastic bag in the ⁠sea is like throwing a ​bullet for the turtles," he said.

For researchers, the turtles are a visible measure of the health of the Mediterranean ecosystem.

As dawn approaches, a final group of hatchlings disappears into the waves. If they survive, some may return decades from now to nest.