Photograph credit: Chris Newbert, Minden Pictures/National Geographic Creative
DISCUSSION: Sea turtles are charismatic species that fascinate and inspire curiosity in people from around the world. These oceanic reptiles are beloved by children and adults alike with their beautiful coloring and unique behaviors. They are often found in many forms of media, with funny pictures of them napping on sponges on the ocean floor, as hilarious helpers in children’s movies, and heart breaking images of unfortunate turtles caught in plastic garbage. These images capture the attention of people around the globe. Tourists flock to sea turtle breeding areas just to watch the hatchlings make their epic journey from nest to ocean, flapping past predators and obstacles on their way to the water’s edge. Tourists, locals, and researchers are able to see the obvious predators to sea turtle populations. Their eggs and hatchlings are prey for beach-going predators, they are known to often mistake garbage bags for food, and their slow swimming pace make them easy targets for boat strikes. They are also often caught in fishing gear, where they can drown if they cannot reach the surface for air.
Recently however, scientists are starting to take notice of another threat to sea turtle survival: temperature. Sea turtles are particularly interesting animals, once they lay eggs in nests underneath the sand on beaches, the temperature inside the nest determines the gender of the baby turtles inside. In fact, NOAA states that at nest temperatures of below 81° Fahrenheit, the baby turtles will be male, for 87° F and above the babies will be female. This slim range ensures that any minor changes to the sand environment is destined to change the turtle’s fate, where one nest normally includes both male and female hatchlings. In recent years, researchers have discovered the effect of rising sand temperatures in Australian beaches where many turtles come to nest. The broods of baby turtles are turning up mostly female, 99% female in Green Sea Turtles to be exact. This result has astonished scientists, worried that the rising global temperatures might induce this change permanently. Temperature changes globally are resulting in Pacific beaches warming, causing the feminization of green sea turtle populations on an alarming scale. (Jensen et al. 2018, Current Biology)
Female and male turtles can have large portions of oceans as habitats, so finding a mate can already be difficult. With the number of male sea turtles on the decline, finding a mate can easily become impossible. Therefore, a population of almost entirely female turtles cannot survive, as without males the populations of turtles will drastically decline into extinction. These gender skewed populations may not be a concern for populations right now, as Green Sea Turtles take around 25 years to mature to reproductive ages. However, many sea turtle populations are already on decline from human impacts on their habitats, such as overfishing and garbage dumping. This decline is expected to continue as long as global temperatures continue to rise at a high rate. The time it takes for turtle species to adapt to changes such as environmental temperatures is on a much longer time scale than the rate of global temperature rise, especially on the Pacific beaches the Green Sea Turtles use for nesting.
Green Sea Turtle species are being impacting by rising sand temperatures in the Pacific, and they are not alone. Some alligator and fish species also have temperature-dependent offspring genders, and they too are expected to show changes in gender ratios in their populations over the next years.
For more information on the Green Sea Turtles and other species impacted click here!
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© 2018 Biologist McKensie Daugherty
NOAA- National Oceanic and Atmospheric Association
credit: National Geographic, Craig Welch