Nocturnal Drama Springs to Life in Shallow Puddles

Puddles seem uninteresting. Any body of water without fish seems barren and unimportant. Maybe there are some mosquito larvae or some unlucky tadpoles squirming around. Hopefully the tadpoles sprout legs before the water evaporates. Hopefully the mosquito larvae stay right where they are. 

But a special type of pond—called an ephemeral pool—is crucial to ecosystems in the Southeast. Wild places across the Smoky Mountain region are speckled with thousands of these ancient ponds that fill with rainwater and snow melt in winter and evaporate by the end of spring.

I recently visited some ephemeral pools with Dr. Josh Ennen, a conservation biologist who works at the Tennessee Aquarium Conservation Institute in Chattanooga. 

His office is at the Institute’s new home, a bright and open building about ten minutes from the aquarium. It’s landscaped with plants native to the Tennessee River Gorge and situated among reedy wetlands between the Tennessee River and the Baylor School.

While we made the 30-minute drive to Ennen’s field site at Prentice Cooper State Forest, he told me a little about himself.

“I was the sort of kid who my mom would feed me and wouldn’t see me before I came home to eat again,” he said. “When we lived in Louisiana I’d be out catching crayfish and turtles in the bayou. When we lived in Illinois I’d spend days looking for snakes.”

Unsurprisingly, Ennen became a biologist, earning a PhD and discovering a new species of turtle along the way.

As we turned from U.S. 27 onto a crunchy gravel road, Ennen told me about the traps he’d set the day before. There were five minnow traps in each of three ponds—two vernal pools and one shallow pond that stays wet during all but the driest summers. The traps were passive, meaning they would only capture the animals that happened to wander into them overnight.

“We’re looking for winter-breeders,” he explained. Some amphibians have internal calendars that tell them when to congregate and breed. Different species emerge at different times. We were out at the height of spotted salamander season.

I’d always thought of salamanders as rare. Despite spending the better part of my East Tennessee childhood picking up rocks and turning over logs, I’d only seen a couple dozen. Even Brian, the protagonist in The Salamander Room, just had the one.

The first vernal pool we stopped at was so unassuming that I wondered why Ennen was slowing down. It looked like water left standing after yesterday’s rain. 

Ennen pulled on his boots and waded into the shallow pool. The first trap was just a few steps into the pool. He picked it up and beamed as he brought it toward me. From several feet away its contents looked like a shivering ball of slimy goo. I could see up close that the trap contained at least fifty shiny black salamanders with patterns of yellow spots running down their backs.

Ennen handed me one of the larger specimens. It was about six inches long with a beefy body and a look of quiet approval on its face.

I was amazed by the number of creatures we’d caught in the first trap of the day. Ennen, apparently, was not. 

“There’s a mass migration from the land around these ponds,” he said, carefully setting the first trap in shallow water and walking toward the next. “Males enter the pond first, looking for females. They come a couple weeks later.” 

The phrase “mass migration” took my mind to wildebeests crossing the Serengeti. Considering the length of the salamanders’ legs, a quarter-mile journey through the woods is probably just as daunting. 

Ennen continued telling me about salamander ecology as he reached the second trap.

“Salamanders account for a surprising amount of biomass,” he explained as he walked back to the edge. “Spotted salamanders spend most of the year on land, living underground and eating worms, crickets, and whatever else they can find. Their migration moves a huge amount of energy from the terrestrial environment into the ponds.”

He lifted the trap he was holding to eye level to show me what was hanging off the side: fist-sized balls of translucent jelly were stuck to the galvanized wire mesh. Snuggled safely inside the jelly were about a hundred salamander embryos. They looked like green fingernail clippings. 

The jelly protects the embryos from the elements, but there isn’t much to protect them—or their soft-bodied, slow-moving parents—from predators. 

“Fish would eat a lot of the larval forms of these salamanders, so they need these ponds without any fish,” Ennen explained. “Since these ponds dry up in the spring and summer, it’s impossible for fish populations to establish here. The salamanders can survive in these pond because they’re fishless.”

It was the middle of the afternoon before we finished checking all the traps. We found about five hundred spotted salamanders and a few other amphibians who were running early or late to their own breeding events.

Prentice Cooper State Forest is a special place, but it’s hardly a pristine tract of untouched wilderness. All the ephemeral pools we visited were visible from the road and seemed totally mundane. And yet those pools, less than a mile from the nearest neighborhoods, are home to a nocturnal drama that has unfolded every spring for thousands of years.

As we drove back to his office, Ennen told me about his young son who wants to be a biologist when he grows up. Though he takes some credit, Ennen really seemed to think that his son is interested in the natural world because he’s growing up in a place where he sees it every day. 

“After getting my doctorate and spending years in the field, I’d never seen a green salamander,” he said. “Then I moved to Signal Mountain, and me and my son were moving a flowerpot one day. And there was one, a green salamander just lying there.”