Vernal pools

Valid and vital: Vernal pools

By Su Clauson-Wicker | Special to The Roanoke Times
Photos by Matt Gentry | The Roanoke Times

In seasonal ponds and ditch puddles around the New River Valley, a life-or-death race is starting.

For many the contest will end in death. But the question of whether resident creatures will fulfill their life’s purpose is up in the air. These ephemeral waters — known as vernal pools because they occur in spring — teem with life, including frog and toad tadpoles, salamanders, dragonfly and mayfly larvae, and sometimes tiny crustaceans. They must mature quickly to lay eggs or leave the pool before it evaporates in the late spring heat.

If spring is hotter or drier than normal, some critters’ life cycle ends.

Why does this matter?

Virginia Master Naturalist Brenda Graff, who started a New River Valley chapter of the Vernal Pool Cooperative in 2015, mentions the frogs and dragonflies’ role in mosquito control. She also says amphibians act as an important barometer of the health of our environment.

“Salamanders and other amphibians have permeable skin. Contaminants can pass right through it, which makes them very vulnerable,” she said. “They are some of the best indicators of what’s going on in the environment and in our water.”

Graff, retired as a librarian with the U.S. Geological Survey in Northern Virginia, moved to Montgomery County seven years ago to enjoy rural life with her sister. She quickly became a Master Naturalist and started two chapters of citizen science programs — Frog Watch and the vernal pool group, which monitors and inventories the life of vernal pools.

Graff loves exploring the outdoors, listening to the trilling and thrumming of frog calls and spotting salamander eggs just below the surface of a pond. But mainly, she’s concerned about wetland creatures themselves, especially those whose precarious existence depends upon the availability of uncontaminated seasonal pools.

An array of wildlife relies on vernal pools as their only habitat. In Virginia, these include wood frogs, Eastern spadefoot toads, fairy shrimp and six species of salamanders, some of them rare or endangered.

These critters, called obligate species, need fish-free freshwater pools where their eggs can hatch in safety. Relative safety, that is. Raccoons, skunks, owls and other animals will feed upon the eggs and creatures in vernal pools as the water recedes.

And then there’s the human factor. Most vernal pools are not protected by wetlands regulations, so they face many challenges including pollution, damage from off-road vehicles and destruction for development projects. When vernal pools are churned into mud pits, the rare species can’t reproduce. These creatures are hard-wired to follow the same path to a vernal pond each year to breed and lay eggs, so they’re out of luck when their pools are destroyed.

On a recent afternoon, Graff trolled the waters of an ephemeral pool in Blacksburg’s Heritage Park with her net for signs of aquatic life. A chorus of peeper frogs began tuning up in the distance, but Graff was finding only mayfly nymphs, small water beetles and a few snails.

“It’s still early,” she said. “I’m glad to see the mayflies. They live only in places with good water quality.”

Graff keeps track of several vernal pools, checking on some along the Huckleberry Trail a number of times a season. In five years, she’s seen at least one disappear, filled in by someone who didn’t realize its significance.

Vernal pond obligates adapt to their situation creatively. The wood frog freezes solid, yet comes back to life in early spring despite having no heartbeat for up to eight weeks. They do this in order to get “a jump” on the competition in vernal pools, mating and laying eggs before most other creatures are stirring.

The eggs of fairy shrimp have been known to survive for a decade or more before hatching if conditions are too dry. When exposed to water, the eggs come out of dormancy and hatch. (In fact, they are related to the “Instant Life Sea Monkeys” marketed in hatching kits as novelty aquarium pets.)

While Graff has yet to spot a fairy shrimp, she can identify the calls of all 15 frogs and toads found in the New River Valley. There’s the spadefoot toad’s nasal “errr” and the high-pitched trill of the American toad. The green frog seems to be plucking a banjo while the wood frog quacks like a duck. It’s all music to her ears.

Vernal pool monitoring is relatively loose — bring a friend for safety, scoop, and count. The Frog Watch program, on the other hand, has exacting rules. Begin your watch 30 minutes after sundown on a day when no branches are moving in wind. Take two minutes to let the frogs get used to you, then start recording calls. Both projects require participants to sanitize their boots against the numerous diseases killing amphibians.

Graff looks out over the pool, searching among the dry grasses and the water for some movement, some new sound.

“Why do I do this?” she asks rhetorically. “I like getting out in nature and seeing the critters. I guess I try to save one little thing at a time. You do the small bit you can.”

Copyright 2020 The Roanoke Times