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Vernal Pools

Temporary, Delicate and Vital Habitats for Wildlife

From the Audubon society of Rhode Island

Vernal pools are something many people have never heard of, yet they are a vital habitat for many native animals. They are essentially temporary wetlands that form yearly in low-lying areas, glacial depressions, or other poorly draining land. They fill with water during the spring snow melt and rising water tables and remain through the spring and summer, only to dry up completely by autumn. During that time vernal pools form the breeding habitat for a large number of creatures, some of which will reproduce no where else.  They can be vast woodland pools, temporary wetlands near ponds, drainage basins, marshes, or simply long existing roadside ditches that fill with spring snow melt. A vernal pool has no stream inflow or outflow.  It is simply a “wicked big puddle.”

spotted salamanderCreatures often arrive at a vernal pool as soon as the ice clears from its surface. Wood frogs emerge from their dormancy in the leaf litter and make their way to the pools for breeding. Their quacking vocalizations can be heard during March after a good thaw.  During the first warm rainy night (above 40 degrees), the mass migration of spotted salamanders occurs. Hundreds of large, chubby, yellow polka-dotted salamanders march down from the uplands to breed in the pools.

Other amphibians such as the gray tree frog, spring peeper and American toad can be found using vernal pools for breeding as well. Such wetlands offer an environment free from many predators that could be found in an established pond or stream. There are no fish or crayfish to eat these creatures or their tiny offspring. Other hunters such as ducks, herons or turtles may sometimes happen upon a vernal pool, but most of the time the creatures there are relatively safe from predation. This makes it a vital breeding habitat.

Come fall, when the beds are dry, there is one more woodland dweller that will emerge to use the vernal pool. The marbled salamander will find a spot at the ‘bottom’ of the dry pool and lay her eggs. Carefully, she will curl her body around her precious eggs and wait, protecting them until the pool fills once again. Then she will return to the upland, leaving her young in the care of the cold waters.

Amphibians are not the only animals to use these areas. Many invertebrates also depend on them. Some familiar insects such as dragonflies and mayflies will lay their eggs in the water so that their larval nymphs can grow up in relative safety. Isopods, amphipods, daphnia, Dobson fly larvae and others can be found in the waters and mud of the puddles.  There is one little creature that can be found nowhere else but in vernal pools. This is the fairy shrimp. These tiny animals distinguish a true vernal pool.  If a vernal pool disappears, all the fairy shrimp that dwell in it will perish.

Vernal pools often disappear as human activity changes the landscape. When houses, roads and parking lots are built, these temporary pools often get destroyed as they are not as easy to discern as permanent wetlands like streams or ponds. Even simply re-grading the terrain of an area can erase the depressions needed for water accumulation. The disappearance of a vernal pool can be devastating to creatures that depend on it. The salamanders that used it will rarely ever reproduce again, as they are instinctually programmed to return to the vernal pool where they were born. Frogs and other creatures may have to travel great distances in the hopes of finding a new place to breed.

Vernal pools are a great place to visit with kids.  You are sure to see a variety of amphibians and hear their different sounds.  Protecting these special places and the upland areas where their inhabitants spend most of the year is important in maintaining healthy, intact ecosystems. You can find out more about vernal pools, as well as conservation efforts of the Audubon Society of Rhode Island by joining us for spring programs and hikes. Visit www.asri.org for more information.

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