It’s vernal pool season

By JOHN JOSE

Spotted salamanders, wood frogs, fairy shrimp and fingernail clams: while this cast of characters may sound like something out of “Alice in Wonderland,” they all exist right here in the Upper Delaware River region. These and other creatures, dependent on spring or “vernal” pools for their survival, display fascinating adaptations to life in these ephemeral wetland habitats.

What is a vernal pool?

Vernal pools form in shallow depressions in the land with the arrival of spring rains and snow melt. Ranging in size from a pool you can literally jump across to hundreds of square feet, they are found on flat areas of hillsides, valley floors, floodplains, wetlands and in forests. Vernal pools occur naturally or in human-made ponds, roadside ditches, canals, abandoned quarries, or foundations of abandoned buildings.

Because they dry out in summer, these water bodies generally cannot support fish. This is one of the most important aspects of what defines a vernal pool, because fish would otherwise consume developing amphibian young.

Soon, in late March or early April, under the cover of darkness, thousands of vernal pool-dependent amphibians, taking advantage of early spring rains that melt snow, thaw frozen ground and fill vernal pools, will traverse the landscape en route to their ancestral breeding pools. As long as we protect vernal pool habitat and effectively address other threats, such as acid rain, these ecological jewels and the unique fauna they support will continue to be a vital component of the rich biodiversity of the Upper Delaware River region.

Denizens of the (not so) deep

Two of the more commonly known vernal pool inhabitants are the wood frog and spotted salamander. Wood frogs, true woodland dwellers, are camouflaged to blend into leaf-covered forest floors. Amazing physiological adaptations allow these terrestrial frogs to overwinter by entering shallow burrows beneath forest leaf litter in the fall and literally freezing solid with the onset of winter temperatures, only to thaw out and emerge on a warm (40-50 degree), early spring, rainy night when they move en masse to vernal pools.

Frogcicles To view a time-lapse video of a winter-frozen wood frog thawing out, search “Frozen Frogs” at pbs.org

During their one- to two-week breeding season, the chorusing males, attempting to attract females, sound like flocks of quacking ducks. Rafts of communally deposited, grapefruit-sized egg masses can contain tens of thousands of eggs, which hatch into tadpoles that graze on algae-covered vegetative matter, until they metamorphize into froglets, emerge and disperse to surrounding uplands. Metamorphosis from egg to tadpole to emerging froglet can occur as quickly as 10 weeks, allowing potentially thousands of wood frogs to emerge from a vernal pool before it dries up.

Spotted salamanders are another common vernal pool inhabitant. Black with bright yellow polka dots and up to nine inches long, these striking, stout-bodied salamanders spend their lives underground moving and feeding within small mammal tunnels and rock crevices, with emergence to the surface triggered by the same early spring rains that bring wood frogs to vernal pools.

Upon reaching a vernal pool, they form “congresses” of breeding adults with females laying egg masses surrounded by a thick gelatinous coating. After a one-to two-week breeding season, the adults disperse back into surrounding woodlands to resume their subterranean lives. Eggs hatch into salamander larvae that feed on the abundant prey of the vernal pool food web and—provided sufficient water levels persist after spring—emerge as sub-adults in mid- to late summer.

[John Jose, a biologist and environmental educator, resides in Beach Lake, PA, and is proprietor of Otter Creek Environmental Education Services ( ottercreekenved.weebly.com ).]

What you can do to protect vernal pools

Give ‘em a lift: Organized citizen groups can act as “amphibian escorts,” literally moving hundreds of animals safely across roadways to reach breeding pools. Citizens can also work with local officials to organize temporary, overnight road closings during vernal pool amphibian migration.

Put them on the map: Register a vernal pool with the Pennsylvania Western Conservancy’s Seasonal Pools Registry ( paconserve.org/rc/sp/ ), a volunteer program to document locations of vernal pools. A similar New York undertaking is the Woodland Pool Steward Program ( dnr.cornell.edu/ext/woodlandpools ) Communities can also map and incorporate locations of vernal pools into conservation planning initiatives.

Get a membership to vernal pool protection: Join your local land trust, such as the Delaware Highlands Conservancy ( delawarehighlands.org , 570/226-3164 in PA and 845/807-0535 in NY), which works cooperatively with landowners to protect all or a portion of their property, including lands that contain vernal pools.

Find out best management practices: The Vernal Pool project of the Landowner Incentive Program (717/948-3839) provides free on-site analysis and recommendations on best management practices to private landowners in Pennsylvania who have vernal pools on their properties. See page 10.

Steer clear: Off-road vehicles driven through vernal pools, even when they are dry in summer, can damage these fragile ecosystems.

Share one with children: Vernal pools are fascinating ecosystems to explore. A dip net and pool guide (such as A Field Guide to the Animals of Vernal Pools ( vernalpool.org/fldgide.htm ) will get you started.