A vernal pool is a body of water that a) becomes dry at some point in the season, most often toward late summer, b) has no permanant visible continuous outlet, and c) contains no fish, as a result of the drying out period. These temporary pools are vital to several obligate species, which count on being able to leave behind offspring in an environment that does not have fish as predators. It should be noted, however, there are predators in these pools, some of them being the obligate species themselves!
These habitats, vital as they are to the creatures that utilize them, are often disregarded as "puddles". They are filled in when they are an inconvenience and, if not located in a zoned watershed, or wetland area, may have little protection from these actions. Fortunately, many towns are adding to their zoning regulations measures to protect these habitats, and the surrounding deciduous forest. Protecting the trees around these pools is important for providing shelter, or a life zone, for the dispersing wildlife. Studies have shown that removal or disturbance of these life zones, which range from 750 to 1,200 feet, can wipe out the vernal pool populations. An excellent resource has just come out called "Best Development Practices: Conserving Pool-Breeding Amphibians in Residential and Commercial Developments in the Northeastern United States". It is by Calhoun and Klemens and is recommended reading for wetland regulating agencies.
The larval amphibians and other creatures must develop fast. It is a race against the disappearing and warming water. As the water heats up, oxygen diminishes, forcing its inhabitants to become air breathing adults, or die. Many don't make it. Water striders feed on surface, which has lowered and brought them closer to their quarry. Salamanders nip at each others tails, either in aggression or for nutrients. By late summer, the pools are empty. The eggs of the copepods and fairy shrimp wait in the leaf litter for the rains to come later in the season. Marbled Salamanders curl around their eggs, awaiting the rains to fill the pool. When the water returns, the eggs hatch, and the salamander larvae swim beneath the winter ice, kings and queens of their domain.
The surrounding trees are vital to a vernal pool, providing the dead leaves that spark the energy transfer in the food chain. Aquatic isopods (related to the terrestrial pillbugs) and caddisflies feed upon the leaves, breaking them down. Bacteria feed on the detritus and dying animals adding important gases to the water. Algae grows, becoming food for developing tadpoles.
Vernal pools are the staging areas for the beginning of the amphibian season. Winter run-off and spring rains fill them and they become alive with action. Insects, such as diving beetles, caddisflies, whirlygigs, and midges search for food smaller than they. Minute crustaceans called copepods and ostracods move in jerky motions just below the surface, while the larger fairy shrimp dance in the sun-warmed pools. Tiny fingernail clams, which have been waiting in the soil, reawaken and begin to filter nutrients from the water.
