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close in image of lime green bubbles with partially formed creatures inside
GREEN LIVING A spotted salamander egg mass in a Virginia vernal pool © Steven David Johnson

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Inside the Alien Worlds of Vernal Pools

Each year, thousands of newly metamorphosed frogs and salamanders emerge from seasonal pools that are as threatened as they are ephemeral.

Summer 2021

Lindsey Liles Freelance Journalist

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A long trek on a dirt road atop the Cumberland Plateau leads to a pool no larger than a living room. Its surface is a dark mirror, reflecting oaks and hickories and patches of Tennessee sky. Rotting leaves and branches sit at the muddy edges of the water; from the outside, all seems quiet and still.

Beneath the water’s surface, spotted salamander eggs glisten pale green. Pickerel frog and spring peeper tadpoles search for algae. It’s late winter now; in a few months, the amphibians will test their terrestrial limbs, climb from the pool and disappear into the forest. Pools like this, crucial for their surrounding ecosystems and the animals that populate them, once dotted the Appalachian Mountains and foothills. But now, their number is declining.

Known as vernal pools, these seasonal wetlands are mostly dry in summer but fill with rainwater and snowmelt in the late fall, winter and spring, when the clay beneath the topsoil is saturated enough to hold water. Though they vary by geology and location, the ephemeral nature of vernal pools keeps them free of fish, making them a vital breeding ground for invertebrates and amphibians, whose life cycles are perfectly synchronized with the annual cycles of the pool—cycles now at risk from climate change and development. Legal protection for these ponds is murky; it’s difficult to protect something that isn’t always there. 

“A normal person would walk across a vernal pool and have no idea whatsoever that anything lies beneath that blackness,” says Michael S. Hayslett, a Virginia vernal pool ecologist. “But beneath the veil lies a truly fantastical world.” 

Image shows above and below water line in a forest, with trees in background above water. Below water line, green algae and moss surround a group of bubble-like eggs, each with a brown nut-like object
Under the Surface A spotted salamander egg mass below the water line of a vernal pool. © Steven David Johnson
brown salamander with yellow spots curls in the dark with dozens of tiny glowing bubble-like eggs against its tail end
Laying Eggs A female spotted salamander deposits a cluster of eggs not far beneath the surface of a vernal pool in Virginia. For reasons biologists don’t fully understand, spotted salamanders—found across much of the eastern United States—often return to the same pool year after year to mate, lay eggs and then return to the forest. In a given year, an adult spotted salamander might spend only a few weeks at the vernal pool—a fleeting but vital part of its life cycle. © Steven David Johnson
Moving Pictures Go beneath the surface of vernal pools to see the life within these overlooked waters.
close up of a nut-like object inside a translucent bubble inside another bubble, against a blurred pale blue background
Inside the Egg A spotted salamander embryo develops within its egg capsule in a pool in Augusta County, Virginia. Already, algae has entered the egg capsule and the embryo’s cells, photosynthesizing and providing the growing salamander with an oxygen boost. Scientist Ryan Kerney studies this symbiotic relationship. “Vernal pools are a gold mine—a unique, rich habitat that can teach us about the rules of life,” he says. “Here’s this common salamander that has been studied for 150 years, and we are still learning from them.” © Steven David Johnson

A Link Formed by Evolution

Vernal pools come to life in the fall, when marbled salamanders arrive during nighttime in droves to breed and lay eggs in the dry depressions. “They are just betting that these pools will fill,” says JJ Apodaca, a North Carolina herpetologist. “Once they do, the eggs hatch and get a head start in growth on larger species, like tiger and spotted salamanders, which arrive sometime between December and February.”

Wood frogs lay eggs by the thousands, and pool-bound fairy shrimp hatch in midwinter. By late winter and early spring, the pools are teeming with life that will flow out into the surrounding forest as the amphibians metamorphose.

Thousands of years of evolution have tied these species, called obligates because of this dependency, to vernal pools’ annual cycles. Along with the many other species that use vernal pools—like newts, spring peepers and even some mammals—these obligates make up a large percentage of the biomass in their respective ecosystems.

Amphibians, Apodaca says, prop up the food chain, forming the link between invertebrates and larger vertebrates, including birds and mammals. “Sure, there is often only a little bit of water in a vernal pool,” he says. “But it’s enough to sprout an extremely complex ecosystem that is disproportionately important to the health of the forest.”

close up of dozens of objects that look like tiny gray brains, inside white bubbles, inside clear bubbles, floating against a blurred peach background
The Jelly Matrix A cluster of Jefferson salamander eggs is suspended gracefully in a protective jelly matrix at a Virginia vernal pool so narrow you can reach your arm across it. The egg capsules, attached en masse to submerged branches or vegetation, measure less than a centimeter each. The dark embryos are still in the early stages of their month-long development. Once hatched, the larvae will hide by day and feed by night in the pool until their gills shrink away and they’re ready to emerge onto land. © Steven David Johnson
in a dark image, 8 salamanders surround a few dozen translucent jelly-like eggs, resting on a bed of dead leaves. All underwater.
Predators Eastern newts prey on spotted salamander eggs at a year-round pond in George Washington National Forest. Though newts use vernal pools, they do not rely on them. Newts are toxic to many fish, which allows them to avoid predation. On occasion, spotted salamanders do breed and lay eggs in permanent ponds like this one, but losses to predation tend to be much higher. © Steven David Johnson
a man stands in a dark pool surrounded by trees. He is bent over towards the water with a camera near the surface of the water. It's daytime.
How these photos were made Long fascinated by vernal pools, photographer Steven David Johnson spent months capturing these images of vernal pools. He practiced camera and lighting set-ups in his studio before venturing out to Virginia vernal pools he knew of from years of hikes with scientists and photography treks. © Anna Maria Johnson

The Race to Save Vernal Pools

Already, though, innumerable vernal pools have been dredged, drained or simply built over, and how climate change will impact them is still unknown. Even small shifts in precipitation patterns can alter their hydrology and timing, causing a mismatch with the species that have evolved to keep pace with them. Protecting the remaining vernal pools, in all their diversity, is therefore critical, says ecologist Hayslett.

Hayslett is part of a community of ecologists and herpetologists protecting the vernal pools that remain by documenting them, conserving surrounding forest habitat as “buffer zones,” and in some cases building new pools. Hayslett helped secure protection for JK Black Oak Wildlife Sanctuary in Virginia, a property with more than a dozen vernal pools. Meanwhile, this year in North Carolina, Apodaca, working with The Nature Conservancy, plans to build 10 pools on Phoenix Mountain, located in a global hot spot of amphibian biodiversity.

close up of a brown partially formed creature with a round body and a tale - a tadpole - against a background of several lime jelly-like circular eggs with semi-developed creatures inside
Tadpoles A wood frog tadpole nibbles on algae-covered spotted salamander eggs in a pool at the edge of Shenandoah National Park. A kind of natural antifreeze helps adult wood frogs make it through frigid winters before they return to vernal pools in early spring to lay eggs. “An individual can survive eight days fully frozen,” says herpetologist JJ Apodaca. “It’s an amazing adaptation for an ectotherm living in a cold environment.” © Steven David Johnson

New Science

Even as conservationists race to preserve vernal pools, scientists are still learning about the species that rely on them. In 2016, Ryan Kerney, a biology professor at Gettysburg College in Pennsylvania, constructed seven vernal pools not far from his laboratory, with the help of TNC. There, spotted salamander eggs grow as they do across Appalachia, tinged with green—a clue to one of the most fascinating known symbiotic relationships. A green algae called Oophila lives within the spotted salamander egg capsules and within embryonic cells and tissues, photosynthesizing and allowing the salamander to grow faster and larger. Kerney is investigating the chemical signaling that induces the algae to move into the cells, and how it might play a role in salamander tail regeneration—one small step toward solving the remaining mysteries of vernal pools.

“The health of these forests is built upon abundance, and abundance is what vernal pools do best: Life in them gathers, forms, grows and then disperses, spreading like a glue that holds the ecosystem together,” says Apodaca. “When we protect vernal pools, we protect more than frog calls, fairy shrimp, and amazing symbiosis: We protect the essence of an Appalachian forest.”

close up of the five-toed foot of a salamander against a black background. Skin is gray-brown with white splotches and appears rough or scaly
Venturing Out The long-toed foot of a Jefferson salamander brushes against debris in a vernal pool in George Washington National Forest on a spring afternoon. Jefferson salamanders are equally comfortable in water and on land—or below it. As members of the mole salamander family, Jefferson salamanders spend much of the year underground, waiting until the weather is just right to make their annual trek to vernal pools to breed. © Steven David Johnson

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Lindsey Liles is an editorial assistant for Garden & Gun magazine, where she has written about conservation and wildlife across the southern United States.