In addition to the known effects of the climate crisis, there are also strange effects that are not known. Florida’s sea turtles, for example, have a huge gender imbalance. More frequent and hotter heatwaves cooking sands on state beaches are causing nearly every new baby to be female, turtle researchers told Reuters.
Female sea turtles bury their eggs in the sand along the coast, where they nest for about two months. The sex of turtles is not determined during or immediately after fertilization, rather the temperature of the beach sand helps determine whether the turtle will be male or female.
When the turtle eggs incubate at temperatures below 27.7 degrees Celsius, the offspring become males. However, female turtles hatch from eggs incubated above 31 degrees. Summers with fluctuating temperatures are required to provide a mix of both, but Florida summers are getting hotter due to climate change.
Florida researchers drew attention to a 2018 Australian study published in Current Biology, which showed that blood samples from turtles were females, particularly turtle hatchlings whose eggs were found in warmer sands. Australian researchers also compared the female population of young turtles with that of older turtles and found more evidence that the male population is declining.
Bette Zirkelbach, director of the Turtle Hospital in Marathon, told Reuters: “The scary thing is that the last four summers in Florida have been the hottest on record. Many biologists studying the juveniles have not been able to find male sea turtles for nearly four years, just found a female sea turtle.”
Without a proper ratio of male and female turtles, breeding seasons will result in fewer offspring to replenish endangered turtle populations. According to the Florida Fish and Wildlife Conservation Commission, between 40,000 and 84,000 nests are set up on Florida’s beaches each year. But only one in 1,000 hatchlings survives to adulthood, and all five species of Florida sea turtles are listed as endangered or threatened.
Biologists point to the sharp decline in male sea turtles that have been living off Florida beaches for nearly a decade. There was not a single male sea turtle born on beaches used for research on Florida Bay or the Atlantic coast from 2015 to 2017, Jeanette Wyneken, director of Florida Atlantic University Marine Laboratory, told the Naples Daily News in 2018. Wyneken and other researchers took 10% of the offspring from a nest to the lab until they were old enough for researchers to check their sex.
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