Stay-at-home science: Location, location, location
One of the features people look for when buying a home is a safe neighborhood — the proverbial “great place to raise kids.”
Wildlife parents are no different; they search for a spot that has everything their offspring need…and as few predators as possible. For certain species, vernal pools are dream properties, even though they offer only seasonal occupancy.
Desirable digs
Vernal pools are small woodland wetlands that form from snow melt and rainfall in late winter or early spring, and sometimes again in fall. Also called ephemeral pools, they dry out at some point in the year, so fish cannot live in them. This is their chief amenity for animals whose eggs and larvae are on the menu of many fish species.
Three types of animals in particular — wood frog, mole salamander (such as spotted, marbled, blue spotted, and Jefferson salamander), and fairy shrimp — rely on vernal pools to reproduce. In fact, vernal pools are defined by these species; if any of one of these is found in a wetland, it’s a vernal pool.
A perilous pilgrimage
Wood frogs spend the winter tucked under fallen leaves on the forest floor. Though it sounds cozy, it’s still bitter cold, and the frogs even partially freeze. Mole salamanders seek safety from the cold in deep burrows below the frost line, entering a state similar to hibernation.
Each spring, on the first night above 45 degrees F after a heavy rain, wood frogs and mole salamanders make their way en masse to the vernal pools where they got their starts, traveling up to a half-mile. This is the “Big Night.” They crowd roadways, and many succumb to car tires. Upset by the annual carnage on roadways popular with amphibians on the move, some communities have built tunnels, while others deploy crossing brigades, to help them pass safely.
A full-service nursery
Once at the vernal pools, the amphibians “congress,” or court each other. The loud “quacking” of male wood frogs fills the air. Following mating, the females lay masses of jelly-coated eggs, often attached to sticks at the bottom of the pool. Then the adults leave, their parenting complete. If all goes well, the eggs will hatch, and the young frogs and salamanders will mature on their own, eating algae, insects, and invertebrates before the pool dries up.
The fairy shrimp is one such invertebrate. Adults lay eggs with tough coatings, called cysts, that lodge in the mud at the bottom of the pool. The cysts can survive the dry conditions of late summer and fall. They can even withstand freezing winter temperatures. When the pool fills again in spring, the next generation of fairy shrimp emerges into the water, just in time to feed hungry salamander larvae.
Looking for change
Amphibian populations have declined dramatically worldwide over the last 30 years. Habitat destruction, the introduction of harmful nonnative species, and disease are some of the suspected causes.
In 2000, the U.S. Geological Survey, the Department of the Interior’s science and research bureau, created the Amphibian Research and Monitoring Initiative (ARMI) to find vernal pools on national wildlife refuges and national parks and track their use by amphibians.
In the Northeast, researchers chose to study spotted salamanders and wood frogs because they’re found throughout the region and reproduce only in vernal pools. By visiting the same pool multiple times every spring and counting egg masses of these species, scientists can estimate population sizes and learn whether they are increasing, decreasing, or stable.
Ten Northeast national wildlife refuges participated in the study from 2004–2016, sending data to USGS researchers. The results showed that wood frog and spotted salamander populations on refuges and parks across the region were relatively stable, although individual sites showed slight changes. Nationwide, however, amphibian populations decreased an average of nearly four percent a year during the study.
USGS researchers continue to collect data. They hope to track changes in vernal pool hydrology — including size and duration of pools — caused by changing climate conditions such as more frequent droughts and floods.
Monitoring has “mass” appeal
Wildlife Biologist Lauren Cruz, at Rappahannock River Valley National Wildlife Refuge in Virginia, has managed a volunteer-led vernal pool monitoring program on refuge lands since 2018.
“We had lots of people looking for hands-on work on the refuge, and this kind of monitoring is a pretty simple task,” said Cruz. “The refuge has 20 tracts spread across the Rappahannock River watershed, and I figured they could help me cover some ground.”
Cruz holds annual workshops to teach people about vernal pools and train them in monitoring. She’s been surprised by the diversity of attendees.
“The first year, we had master naturalists, a high school teacher, and a mother and son who were looking for a project to enjoy together,” she said. “And last year, we had people from three master naturalist chapters, three schools, and Rappahannock Community College.”
Surveys take place from mid-February to mid-April, with a pair of volunteers visiting each pool three times. They count wood frog and spotted salamander egg masses and use a small net to drag the edge of the pool for larvae. They also record environmental conditions, including pool size, water pH and temperature, weather conditions, and plants present. At the end of the season, Cruz compiles the results for all refuge tracts and sends them to USGS.
Cruz points out that you don’t need to volunteer at the refuge to track vernal pools.
“The cool thing is that people can monitor vernal pools in their own neighborhoods and submit their data through CitSci,” said Cruz. “Researchers at USGS, as well as state wildlife agencies, can access it and use it in their work.” (Note: The project on the website is for Virginia only; the public can also submit vernal pool data through iNaturalist.)
Real-world learning
Rappahannock High School Teacher Carolyn Reiner offered vernal pool monitoring on the refuge as a service project to members of her Science National Honor Society group.
“The vernal pool study is one of those citizen science opportunities that allows them to contribute to an actual research database,” said Reiner. “They get to see the connection between data and environmental action, and it’s really cool.”
Reiner hopes to incorporate the monitoring project into her environmental science classes.
“Hopefully next year!” she said. “I have big plans.”
Diving into vernal pools
Vernal pools may be ephemeral, but they’re also endlessly fascinating. To learn more:
• Enjoy a reading of The Secret Pool by Kimberly Ridley, beautifully illustrated by Rebekah Raye.
• Sing along to “Come with Me to a Vernal Pool” by Rachel Dunham.
• Glimpse vernal pools through the eyes of their occupants in the graphic novel A Year in My Life, by Vern L. Poole.
• Print and color your own field guide to vernal pools to discover the variety of life they support.
But the best way to get to know vernal pools and their wildlife is to explore them. Take a walk in the woods, and look for flooded areas. Search for the distinctive jelly masses of frogs and amphibians. Bring along a clear plastic pail or disposable food container to dip water from the pool. Check for tadpoles, salamander larvae, and tiny fairy shrimp. Return in a few weeks and see what’s changed!
A choice listing
A seasonal home at the water’s edge may seem ideal to many people, but for most amphibians, in the water is the place to be come spring. Vernal pools offer safe retreats, with childcare provided — something human parents would no doubt find attractive.
