Tadpoles & Vernal Pools

Tadpoles & Vernal Pools
Vernal Pool (PotW Lrg)

It probably comes as no great surprise that these tiny tadpoles will eventually develop legs and assume their mature form as frogs or toads. Both types of amphibians are perpetually bound to the water, if not by their preference in habitat then by the need for a place to develop into adults and lay eggs of their own. This affinity for water, however, can oftentimes put them in grave danger.

Fish can be a huge problem for breeding amphibians. They’ll feed directly on the eggs of frogs and toads and continue feeding on tadpoles after the remaining eggs hatch. Larger fish will even prey upon the full-grown adults (over the years, I have caught countless largemouth bass on lures that are designed to look identical to medium-sized frogs). Suffice to say, life in ponds with stable fish populations isn’t easy for frogs and toads. “Vernal pools” offer something a safe haven for amphibians, though.

Vernal pools are shallow depressions in the ground that fill each Spring with a combination of rain run-off and melted snow. If you go hiking early in the year, you’ll probably spot these pools beside the trails occasionally. Unlike ordinary ponds, vernal pools aren’t usually fed by brooks or springs, so they will begin to evaporate as hotter, drier months approach. Many are entirely dried up by summertime, but it is this impermanence that makes them so useful to frogs and toads as a secure breeding ground.

Since most vernal pools are dry for the greater portion of each year, they cannot support a population of fish. With such a dire predator out of the picture, frogs and toads are able to lay their eggs in relative safety and tadpoles have just enough time to develop and hop away before the pools start to dry up. Many of those adults will eventually return to the same place to lay their own eggs, so certain vernal pools have likely been home to countless successive generations of frogs and toads for decades, if not centuries.

Sadly, a great deal of vernal pools have been lost to extensive land development in recent history. The effect on frog and toad populations varies between species. American Toads, Bullfrogs and Spring Peepers are quite happy to breed in vernal pools, but they are also adaptable enough to make use of ponds and swamps. Other species, including Wood Frogs and Eastern Spadefoot Toads (known as “obligate species”), depend exclusively upon vernal pools to successfully reproduce. With the loss of vernal pool habitats, the population numbers of these creatures have been declining with each passing year; their continued existence in the future is no longer certain.

About this Photograph
Photograph of Tadpoles © 2011 J.G. Coleman Photography. View more photography by Trails of Freedom Chief Researcher, Justin Coleman, at J. G. Coleman Photography.