Ponds that vanish and reappear, animals that go dormant and return to life—vernal pools feel a bit like spring magic, but they’re 100 percent real.
These ephemeral habitats, found along the U.S. West Coast and throughout the Northeast and Midwest, form in natural depressions that have suitable soil for holding water. (See our beautiful photos of spring landscapes.)
They’re unconnected to streams or other water sources, filling up with rain or melted snow in spring and evaporating in summer, usually by July.
“The first time I saw a vernal pool, I was walking through the woods and saw the clouds reflecting from the forest floor,” Evan Grant, a research wildlife biologist with the Amphibian Research and Monitoring Initiative of the U.S. Geological Survey, says by email. “I looked closer and it was a pond in the middle of the woods.”
Vernal pools always occur in the same spot, usually on a gently sloping wetland, and can vary greatly in size, from a shallow lake to a tiny puddle. Grant has seen one the size of a coffee can.
But size doesn’t matter to the many animals that depend on them. Even in that coffee can-size pool, Grant says, there were salamander eggs.
On the vernal equinox—the first day of spring—we’re taking a closer look at the wildlife that thrives in these whimsical water bodies. (Related: "When is the Vernal Equinox? Everything About Equinoxes.”)
Species that require vernal pools to complete their life cycle are called obligate or indicator species, and can include amphibians such as spotted salamanders and wood frogs. Many amphibians will return to the same pool in which they were born to breed.
Crustaceans, including the inch-long fairy shrimp, also depend on these seasonal pools, laying their eggs in the water.
Some shrimp hatch early and sink down into the mud. As the soil dries, the animals enter a state of diapause—or dormancy—that can last for decades, Tim Maret, an ecologist at Shippensburg University in Pennsylvania, says by email.
This guarantees that “even if conditions are bad and no reproduction occurs, there should still be more fairy shrimp the next year,” he says.
Fish out of water
One animal you might expect to find in a pond isn’t present in vernal pools: Fish.
Fish can’t survive in these ecosystems because they eventually dry up, and fish always need to be in water, James P. Gibbs, a conservation biologist at the State University of New York in Syracuse, says by email.
That's a good thing for amphibians, whose eggs and tadpoles would otherwise become fish food, he notes. (Read about the bizarre newts that spend their lives as babies.)
But other predators stalk vernal pools, such as water snakes, which Grant has seen snacking on wood frog eggs.
Unfortunately for the host of creatures that depend on them, vernal pools are vanishing permanently in some areas due to urbanization, agriculture, and other causes. According to the U.S. Environmental Protection Agency, more than 90 percent of California's vernal pools have disappeared.
But they persist in other areas, including southern Pennsylvania, where “the frogs have started to call," Maret says. On rainy nights, the sound can be deafening.
“It’s spring!” he says.