In the wild: The promise of new life in our little woodland pools

The woodland pools in our region (often misnomered “vernal pools”) are temporary bodies of water that fill in autumn and springtime in the wild.

To the casual observer, they appear innocuous enough. Closer inspection, however, reveals something truly inspiring.

Among the first creatures to appear are “fairy shrimp,” tiny (one inch or so) cousins to the marine shrimp that we know from our appetizer plates. The miracle here is that these tiny crustaceans have existed on Earth since the Cambrian Period, over 500 million years ago, and their dry eggs can survive decades, possibly centuries out among the leaf litter of our forests, hatching only after these temporary pools fill with springtime water from melting snow and rain. The adult shrimp then live for only a couple weeks. Like other temporary woodland pool users, they wouldn’t survive in the presence of fish, so they’re what we call “obligate users” of temporary pools, where hungry fish can’t survive. They’re actually holdovers from the days of oceans covering more of our continents.

Equally miraculous obligate springtime users of woodland pools include wood frogs, beautiful brown frogs that spend all year, except for their short couple-weeks’ breeding season, in forested areas away from waterbodies. When winter arrives they simply snuggle down under a few leaves and allow their bodies to freeze! Think of this past winter’s extreme cold and imagine being a soft frog beneath a thin layer of forest leaves. Wood frogs and some other species do this by suddenly manufacturing an abundance of glucose upon freezing, which is a natural antifreeze that keeps their fluids from crystalizing and expanding, thus allowing them to survive for eight months or longer in a frozen-solid state. When springtime sun warms the forest floor through the bare branches, these frogs awaken and blast downhill toward these pools, immediately engaging in their quacking breeding calls... These are the frogs that make woodland pools seem to teem with invisible ducks.

Autumnal pool users:

In our region, some species breed only in the autumn in these same temporary woodland pools, which is why literate biologists suggest avoiding using the term “vernal” (springtime) to describe them. The marbled salamander is one such species, and they can find breeding to be tricky after a dry summer that yields no water in our temporary pools, as they lay in wait for autumn or winter rains and snow with their fertilized eggs. There is an advantage to autumnal breeding, however: These larvae develop over the wintertime, feeding on invertebrates in wet, frozen mud beneath the surface. In springtime, after the vernal (springtime) breeders’ eggs have hatched, these now larger marbled salamander larvae feast on the newly hatched amphibian (frog. toad and salamander) larvae.

Nature, while immutably cruel, imperfect and, frankly, a jungle, always brings inspiration in its promise of new life in its ecological communities. No wild community better examples this than our woodland pools. If you’re out on a hike this month or next, stop by one of these pools, especially with your children. Kids tend to be attracted to tiny communities of critter activity.

Jay Westerveld

Sugar Loaf

Jay Westerveld is an internationally recognized ecologist and educator who has been researching natural and cultural history for over 40 years throughout America, Europe, Asia and the South Pacific.