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Ants in the Nest: A Possible Emerging Pressure on Sea Turtles

Loggerhead sea turtle, Cumberland Island, Georgia

Georgia’s barrier islands are an attractive location for loggerhead sea turtles (Caretta caretta) to lay their eggs. However, red imported fire ants and native ants may depress the emergence of sea turtle hatchlings, especially in nests near dune vegetation. A new study published in Environmental Entomology examines the interactions of ants with sea turtle nests and offers recommendations for reducing ant-related risks in sea turtle conservation. (Photo courtesy of Charles Braman)

By Melissa Mayer

Melissa Mayer

Melissa Mayer

Hatchling sea turtles face huge perils on the journey from nest to sea. They’re also sometimes beset by a tiny one: ants.

In a new study published this month in Environmental Entomology, researchers looked at the interactions between ants and loggerhead sea turtles (Caretta caretta) on Georgia’s barrier islands.

It turns out red imported fire ants (Solenopsis invicta) and 13 species of native ants showed up in loggerhead nests—and nests with ants had lower nest emergence success. This is likely density-dependent and influenced by how close the nests are to dune vegetation, the researchers say. Their new recommendation to maintain a 1-meter buffer between vegetation and relocated sea turtle nests may help bolster hatchlings.

Unexpected Diversity

Charles Braman

Charles Braman

The team worked with the Georgia Sea Turtle Cooperative (GSTC) over two seasons, relying on volunteers to scoop up ants found in or around sea turtle nests they were monitoring or relocating. Then, lead author Charles Braman had the tricky task of identifying all those ants.

“It can definitely be challenging initially,” says Braman, who worked on the study while a student in ecology and entomology at the University of Georgia and is now a research assistant at the Riparian Invasion Research Laboratory at the University of California at Santa Barbara. “A lot of ant IDing is numbers of hairs or length of hairs in specific spots—as with many insects—but once you figure out what your cast of characters should be, and you can narrow it down to the few key traits that you really need to look for, it starts to get much easier.”

Red imported fire ants were the most frequently encountered ants overall. After that were native ants like Dorymyrmex bureni, Forelius pruinosus, and Pheidole morrissi, plus 10 other native species encountered less frequently.

While the team expected to see the fire ants, finding all those native species interacting with sea turtle nests was unexpected. The other surprise was that ant activity didn’t seem to disrupt hatching. It did correlate, however, with lower emergence success, especially in nests close to dune vegetation.

Emergence success means the hatchling is able to get out of the nest on its own. An unsuccessful emergence could point to a mortality event or to a hatchling that needed a boost—for instance, if it got caught up on a plant root and a GSTC worker freed it.

Those roots may be key. Braman says one possible scenario is that ants follow roots into a nest, which is filled with soft sea turtle eggs and fluid to keep them healthy. That’s probably a good water resource for the ants. When the eggs begin to hatch, all that movement could spark territorial behavior in the ants.

The team didn’t tease out the influence of specific species of ants—or whether ants directly affected emergence versus just showing up at nests where hatchlings were struggling. It’s possible tiny scavenging ants pose less of a threat compared with strong-mandibled big-headed ants or fire ants, which Braman describes as a “sting first, ask questions later organism.”

Getting Ahead of the Ants

The team sees this as a rare chance to outpace a potential problem. “We have an opportunity to get ahead of an emerging pressure on these organisms before it becomes a large pressure on them,” says Braman. “Most of our encounters came from islands that had more than 100 sea turtle nests on them … so it benefits us to better understand which species may actually be problematic versus which species are not before it’s a bigger challenge.”

Loggerhead sea turtle nesting on Cumberland Island, Georgia

Based on findings from a study looking at the interactions of ants with sea turtle nests, researchers recommend leaving a 1-meter buffer zone between dune vegetation and the sea turtle nest when relocating a nest, to avoid potential negative effects of ant presence, which their data shows is correlated with reduced nest-emergence success for turtle hatchlings. (Photo courtesy of Charles Braman)

As conservation efforts pay off in more sea turtle nests, this density-dependent scenario in which ants run into sea turtle nests and affect hatchling emergence could become more frequent. Plus, other sea turtles may build riskier nests. “[Loggerheads] have a preference for big, open sand,” says Braman. “It’s likely that, for species that nest further in vegetation, there’s a stronger effect. We have almost a best-case scenario of turtles, and still there is an effect that we observe.”

Based on their data, the researchers recommend leaving a 1-meter buffer zone between dune vegetation and the sea turtle nest when relocating a nest. That’s a better intervention than using ant bait, especially since so many nests host native ants, and baiting could boost fire ants by reducing native ant populations.

For Braman, offering a tangible recommendation to support conservation workers was a high point. “You have a lot of research that just sort of comes in and investigates and then rides off into the sunset,” he says. “So, for all the different projects that put so much of their time and effort into helping us with the study, it’s nice to have a result that hopefully helps them in their work.”

Melissa Mayer is a freelance science writer based in Portland, Oregon. Email: melissa.j.mayer@gmail.com.

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