New study shows alligators aren’t all that’s lurking in Georgia’s swamps

New research from the University of Georgia’s Odum School of Ecology and Marine Extension and Georgia Sea Grant suggests there may be elevated levels of mercury in Georgia and South Carolina waters.

In studying alligators from the Okefenokee Swamp, Jekyll Island and Yawkey Wildlife Center, UGA researchers found high levels of mercury, prompting concerns about the levels of the heavy metal in the environment.

“Alligators are very ancient creatures, and we can look at them in these areas as an indicator of what else might be happening in the ecosystem. Studying them can relate to many different things in the food web,” said Kristen Zemaitis, lead author of the study and a graduate of the Odum School.

The presence of mercury in these waters not only impacts the health of the alligator but could have dangerous health effects on the other creatures relying on these waterways for food, including humans.

Mercury concentrations matter for the bigger picture

Trace amounts of mercury, a potentially harmful element, are often found in runoff and precipitation downstream from major industrial areas. Previous research has shown accumulating levels of the heavy metal in smaller animals in Georgia swamps but not as much is known about animals as high up in the food chain as the alligator.

Through studying the diet and analyzing blood samples of more than 100 alligators, across several months, the researchers found that where the alligators resided made a difference.

Alligators in the Okefenokee Swamp had mercury levels that were eight times higher than the other two research sites.

"If (mercury) builds up, it moves through the food web and creates the perfect storm. That’s what we have in the Okefenokee.” —Jeb Byers, Odum School of Ecology

“That’s one of the results from the study that was most striking to me,” said Jeb Byers, co-author of the study and UGA Athletic Association Professor in the Odum School. “Mercury is a neurotoxin that is very lethal to organisms. If it builds up, it moves through the food web and creates the perfect storm. That’s what we have in the Okefenokee.”

Mercury concentrations in alligators show that the toxin can easily move up the food chain.

Whether it’s gators themselves or the fish they cohabitate with, this study signals caution to any humans who may fish or hunt in the area. Although the Okefenokee Swamp is a wildlife refuge, it shares waters with the Suwannee and St. Marys rivers, which means there may be a heightened risk of mercury contamination in fish and other animals residing in the waters.

“Mercury contamination can be a high concern for the people who can be consuming a lot of fish or game species from the rivers, swamps or oceans that have high mercury. In any given ecosystem, there are some organisms that can tolerate only very little amounts of mercury, which can result in neurological issues, reproductive issues and eventually death,” Zemaitis said.

Alligators’ age matters in mercury measurements

It wasn’t just where the alligators lived — how long they’d been there mattered too.

The researchers discovered that mercury concentrations were more prominent in larger, older gators. That wasn’t just from absorption over time but presumably from the alligators consuming greater amounts of creatures already contaminated with mercury.

 

UGA researchers examine one of the alligators in the study. (Photo by Jeb Byers)

“Organisms can accumulate dangerous levels over the course of a lifespan. However, we often account for age but not diet,” said Benjamin Parrott, an associate professor at UGA’s Savannah River Ecology Laboratory and Odum School and co-author of the study. “What our study shows is that as alligators grow and start to eat larger animals, this increases the amount of mercury they accumulate.”

As for smaller, young alligators and hatchlings, the story was surprisingly the same. Mercury levels seemed to be inherited by offspring.

“Some of the hatchlings had really high levels of mercury which we were not expecting. Mothers are passing toxins and heavy metals into the egg yolks during reproduction,” Zemaitis said.

Research signals need for future studies on mercury impact

It’s likely not just alligators being influenced by high levels of mercury in the environment, Zemaitis said.

“Now that we know this about one of the apex predators in these systems, we wonder what else is being affected?” she said. “I would like to investigate more about where exactly the mercury is coming from and how it’s getting into the ecosystem. It would be really great to pinpoint a prominent source and also see how it’s affecting other animals in the ecosystem.”

The study was funded by the Jekyll Island Authority and the Okefenokee Swamp Park, and includes co-authors Thomas Rainwater, of the Tom Yawkey Wildlife Center and Clemson University; Yank Moore, of the Conservation for Jekyll Island Authority; and Kimberly Andrews, a coastal ecology specialist with UGA Marine Extension and Georgia Sea Grant.

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