At 6 p.m., the Costa Rican beach was sweltering. Jack Suss, a research assistant at Drexel University, wiped his face and started digging, keeping a trained eye on the sand below.
Suss was part of a university-sponsored expedition to determine the effect of rising temperatures on leatherback turtle populations. His main task was to excavate turtle nests, counting how many in the clutch had survived the two-month incubation period.
At 2 feet below the sand, bits of egg littered the nest -- telltale signs that hatchlings had broken through their shells and made it onto the beach. At 3 feet down, however, the results didn't appear as promising. Dozens of white eggs the size of pingpong balls blanketed the very bottom of the enclave.
Photo courtesy of Massachusetts Energy and Environmental Affairs
Suss cracked a few of the eggs open. Some fetuses had matured only slightly, still full of nutritious yolk. Others were already miniature turtles with eyes and flippers. All were the victims of high temperatures.
Changing climate patterns can't explain all hatchling fatalities, but Suss and his supervisors, Vincent Saba and Pilar Santidrian Tomillo, believe they're a problem that could ultimately drive the local species to extinction.
According to their recent paper published in Nature Climate Change, the effects of rising temperatures and decreased rainfall may reduce leatherback turtle populations in the eastern Pacific by up to 75 percent in the next century, making disappointing excavations like Suss' all the more common.
In the past, fishing and poaching have been the main causes of leatherback deaths, putting the species on the endangered list. Even accounting for these threats, climate change will be the next big hurdle facing the turtles, said Santidrian Tomillo, the science director for the Leatherback Trust and an author of the study.
Baking turtles within their shells
The paper, a compilation of Intergovernmental Panel on Climate Change reports, Earth system models and population dynamics, demonstrates that a warming climate significantly increases the mortality of eggs and hatchlings. The rise in temperatures creates an inhospitable environment for turtle eggs, essentially baking fetuses within their shells and making it difficult for the hatchlings that do survive to dig their way out of deep nests.
"Overall, the hatching success rate is very low, and that's worldwide," Santidrian Tomillo said. "As it's getting warmer and drier in this area, fewer eggs are developing."
She added, "Some [leatherback] populations may survive, but most of them could become locally extinct."
The effects of climate change on turtle populations are already apparent, Suss said. In a May study published in PLoS ONE, researchers documented Costa Rican leatherback populations as they shrank from about 1,500 females in the 1980s to about 50 today.
Leatherbacks, the largest turtles in the world, have survived significant climate alterations before. Weighing in at more than 1,500 pounds as adults, the species has been around for more than 100 million years. However, Saba warned, in this case the turtles may not have enough time to adapt to the projected warming of almost 2.5 degrees Celsius.
"One century is definitely not enough for natural selection to work on a long-lived animal like a sea turtle," he said.
An explosion of females
A higher local temperature may also affect the gender of turtle populations, although the study says this is unlikely to be a major problem. A turtle's sex depends on the temperature of its nest during development. Higher temperatures, such as those typically associated with El Niño, produce female turtles, whereas cooler climes introduce males.
On the beach, Santidrian Tomillo calculated that about 90 percent of hatchlings have been female this year. Fewer males means that the upcoming turtle populations will have less genetic variability, a reality that could cause inbreeding and thus species stagnation.
To balance the male-to-female ratio and reduce hatchling mortality rates, scientists and conservationists may have to manually irrigate nests, which will keep temperatures below the sand at advantageous levels. Other options include incubating the eggs in a laboratory or climate-controlled hatchery.
These mitigation techniques aren't without controversy. As an endangered species, leatherback turtles are strictly regulated by the Costa Rican government, Saba said. Significant alterations to their natural environment would have to be cleared by officials. They would also require resources that researchers often don't have.
Still, Suss said, something has to be done.
"On the beach where the nests are, they don't have anywhere to move; they're stuck," he added. "They have to deal with whatever sort of environment comes."
People seem to think large organisms aren't going to be affected by climate change as much, Suss said, but this study demonstrates otherwise. Everything in the ecosystem is intertwined, he added, so when a species is removed, there are always consequences.
Reprinted from ClimateWire with permission from Environment & Energy Publishing, LLC. 202-628-6500. E&E Publishing is the leading source for comprehensive, daily coverage of environmental and energy issues. Click here to start a free trial to E&E's information services.