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Climbing from Puddles of Life

In vernal pools, renewal is under way

Juanita Robinson and her friend Rita Thaxton explore a vernal pool with Juanita’s grandchildren, above. <<photo by Lindsay D.F. Hollister>>

This time of year, marbled salamander tadpoles are already swimming through the shallow waters of vernal pools. Vernal pools are temporary wetland habitats in our forests. They hold water long enough during spring to attract special animals that you aren’t likely to see anywhere else. Then the pools dry up, so fish and other large predators can’t live there.
    What is that? visitors want to know of the oddities they see when exploring a vernal pool at Jug Bay Wetlands Sanctuary.

Sarah Alley inspects water taken from a vernal pool at Jug Bay Wetlands Sanctuary.

    Four species have adapted to lay their eggs in vernal pools on the mid-western shore of Maryland: wood frogs, marbled and spotted salamanders and fairy shrimp. An unusual toad called an Eastern spadefoot also appears after flood rains. Their lifecycle is quick; an Eastern spadefoot egg can hatch, grow as a tadpole and metamorphose all in two weeks.
    Each fall, on a rainy night near September 15, marbled salamanders migrate to their dry pool where females lay clutches of eggs under logs. They know where to go because they hatched out of the pool two to 15 springs earlier. When water fills the pool in late winter, the eggs start developing, giving the marbled salamander tadpoles a head start on the coming season.
    As early as February, vernal pools fill with water, and wood frogs migrate to them. A population of wood frogs congregates for just a few days. Their quacking song rising from the forest day and night is unmistakable. As quickly as they appear, they disperse back to the forest floor, leaving softball-sized squishy floating egg masses that will hatch into tadpoles in less than 30 days.

Feathery external gills give the spotted salamander tadpole a lion’s mane appearance, which distinguishes it from frog and toad tadpoles.

    Around that time, you might see spotted salamanders migrating on a rainy evening. The males and females dance silently after reaching the pool. Then females attach tennis ball-sized egg masses to underwater twigs and vegetation. Once hatched, the spotted salamanders’ feathery external gills give their head a lion’s mane appearance. This adaptation distinguishes salamander tadpoles from frog and toad tadpoles.
    As spring progresses, other aquatic animals are drawn to vernal pools for food, water and shelter. Dragonflies hunt, wood ducks swim, turtles forage, newts wriggle and snakes slither. This temporary web of life is ever-changing.
    In these short-span pools where survival is tough, species have developed amazing fitness.
    As a pool fills with water, fairy shrimp hatch from special eggs, called cysts. By April, these fascinating crustaceans have grown to over an inch long, and females carrying eggs can be seen fluttering underwater. Fairy shrimp die when the pool dries out. But the cyst eggs they leave behind are remarkably tough. Cysts have hatched after exposure to temperatures as low as –342 degrees F, and as high as 178 degrees F. After 15 years on the shelf, a fairy shrimp cyst can still hatch.
    From autumnal marbled salamanders to quacking wood frogs’ pool party to spotted salamanders and fluttering fairy shrimp, the vernal pool season is here this month, gone the next — but full of life in between.
    Ages 8 and up can learn more about fairy shrimp or join a vernal pool research day at Jug Bay Wetlands Sanctuary:

Hollister is a naturalist and volunteer coordinator at Jug Bay Wetlands Sanctuary.