CMLT is Searching for Vernal Pools

By Roger Rittmaster


Vernal pools are an important feature of the Maine woods, but what are they, and why are they so valuable?


Vernal pools are temporary bodies of water that fill up from autumn through the spring and usually dry up during the summer. Because they are not permanent, fish and predators such as bullfrog tadpoles cannot

survive in them. This creates a niche in which the larvae of amphibians and insects that don’t require year-round water, but are easily consumed by predators, can flourish. To be fully functioning vernal pools, they need to be situated in a forested landscape containing a deep leaf litter and decaying logs that provide both food and shelter for the adult animals whose life begins in the vernal pool.


Animals that utilize vernal pools for reproduction are “explosive breeders.” This means that many more eggs and larvae are produced than will survive. The insects and other animals that breed in vernal pools form the basis of a food web that supports much of the surrounding forest. If the vernal pools vanished, the biodiversity of the surrounding forest would be greatly diminished.


Two key species that depend on vernal pools for reproduction are wood frogs and spotted salamanders. In the early spring, as soon as the ice melts, and even before the snow has disappeared, wood frogs migrate en masse to vernal pools. This migration and mating ritual usually occurs during the first two weeks of April in Mid-Coast Maine, when there “quacking” calls can fill the night. And after a week or two, they retreat back to their forest hideouts, leaving behind masses of eggs, from which tadpoles hatch in 3-5 days. The tadpoles can mature Into frogs in as little as 40 days. Wood frogs live for 3-5 years.

Spotted salamanders also migrate to vernal pools in early to mid April, waiting for the first warm rain (> 40 fahrenheit). During the early evening of this “Big Night”, hundreds of spotted salamanders, often 6-8 inches long, return to their natal vernal pools. The males deposit a sperm packet on the bottom of the pool, which is picked up by the females to fertilize their eggs. After a few days to weeks, usually during the next warm rain, the salamanders disappear back into the woods. The eggs take up to 6 weeks or more to

hatch, depending on water temperature and larvae take 2-4 months before they leave the pool. Adults can live up to 20 years and may not breed every year.

To maintain a stable population, each adult female wood frog or spotted salamander needs to produce in her lifetime only two offspring that successfully reproduce. Hence, the vast majority of these two species, as well as the other inhabitants of vernal pools, are destined to become the base of a large forest food pyramid. This is why CMLT wants to document the presence of vernal pools on their properties. And for land that is not yet protected, the presence of vernal pools increases the importance of preserving that land.

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