A large, long-term study has found “alarming” levels of chemicals in Great Barrier Reef sea turtles, leading to wider concerns over the health of the reef environment in general, according to The Guardian. Scientists and conservationists are now calling for further testing on nearby bays and estuaries, and consistent monitoring of the turtles, “as an indicator of the health of the reef itself.”

In 2012, over 100 dead or sick turtle washed themselves up on beaches in nearby Upstart Bay, and the mass-stranding led scientists to begin what is among the largest turtle research projects to date, lasting five-years.

They tested two nearby coastal turtle populations, and compared them to the results from turtles at a “comparatively pristine site,” an island 550 kilometers away.

WWF (World Wildlife Fund) Australia has now published the final results of the study.

Both coastal populations showed higher levels of metals like antimony, cobalt, and manganese, and exhibited signs of poor health. In one of the two populations, cobalt levels were 25 times higher than in the remote island population, showing the highest levels ever recorded in a vertebrate species.

Cobalt is necessary for humans and animals, but can also be toxic in large amounts.

According to Cesar Villa, a Griffith University research fellow, further investigation will be necessary to determine the cause of the contamination. However, run-off from mining or other industrial activities is one possibility.

It’s unclear whether these chemicals were at fault for the mass-stranding in 2012, but Villa said the results demonstrate there is “no excuse not to do large-scale, non-target screening” for contaminants in the reef as a whole.

The samples came from turtles captured two years after the 2012 incident.

“These were the survivors that were still struggling along, so we didn’t know when it started and how bad that first batch [could] have been,” Villa said.

“We have shown turtles are good indicators of reef health because they absorb chemicals in their environment,” said Christine Madden Hof, WWF Australia’s marine species project manager.

“If we found all these contaminants in just two coastal locations what’s happening in the reef’s other major bays and estuaries? What effects are chemicals having on other wildlife in these waterways?”

The Great Barrier Reef is already gravely threatened by climate change, with nearly half of the coral having been bleached and killed since 2016. Warming ocean temperatures have killed algae, which coral relies on for food.

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