New research shows that environmental stressors caused by human activity are harming coastal green turtle populations. Heavy metals in particular are causing problems.

The research results, published in the journal Science of the Total Environment, were compiled by a team that was evaluating the health of sea turtles after a devastating mass death of green sea turtles in Australia.

“We found evidence of heavy metals—particularly cobalt—in sea turtle populations where we also saw signs of illness,” said study lead author Mark Flint of Ohio State University. “Though we can’t be sure what caused this, there were cyclones and major flooding in this part of Australia two years prior to the start of our study, and that could have drawn out sediment rich in heavy metals that had been lying in rivers and streams benign for the past 50 years.”

Green sea turtles are an endangered species. They are among the largest of the sea turtles and can grow to a weight of almost 400 pounds, and they’re named for the greenish color of their fat, not the color of their shells or bodies. They’re found primarily in tropical and subtropical waters—the one in the photo accompanying this article was photographed off the Hawaiian coast. Large populations of green turtles also feed and rest on Australia’s Great Barrier Reef.

Flint’s team examined turtles in two Australian bays, Cleveland and Upstart, that were known to be impacted by human activity. They compared these turtles with others living in a remote, “pristine” area. They started their research by conducting physical exams and blood tests on the turtles, looking for evidence of contaminants or illness. When they found dead turtles, they performed extensive necropsies looking for factors that led to the animals’ deaths.

The researchers also counted barnacles on the turtles’ undersides as Flint’s previous work had shown that high barnacle counts on turtles’ undersides correspond to poor health. Why? Because when green turtles are healthy and feeding normally, their visits to the sea floor typically do a good job in scraping the barnacles away. When they’re not eating well, the barnacles build up.

“An unhealthy turtle often has trapped air in its shell and is buoyant, meaning it can’t dive down for food. It’s almost like a balloon. Also, a turtle that can’t dive sits on the surface of the water, where algae and barnacles can grow better,” Flint said.

In the green sea turtles at Cleveland Bay, they found elevated levels of creatinine kinase, an enzyme that typically rises after muscle injury or illness. In the Upstart Bay turtles, they found elevated white blood cell counts, indicating that they were fighting infection.

The researchers suspect that the unhealthy blood test results seen in turtles in areas affected by urbanization, farming, and industry are suffering from contaminants that are being shed into the affected waters.

Why is research on sea turtles so important? Because they have long lifespans and tend to stay in one place, so they can serve as proxies for the broader environment—a sort of canary in a coal mine.

This research will give conservationists and marine biologists a better understanding of sea turtle health and response to environmental stressors, the researchers said, which will enable them to better assess turtle health in the long run. It should also help decision-makers such as politicians and developers to provide environmental mitigation strategies, Flint said.

Photo: Shutterstock