An Introduction to Seasonal Pools
Seasonal pools are wetland habitats where some of the state’s most recognizable reptiles and amphibians can be found. Seasonal pools are small, shallow wetlands that do not have a permanent inlet or outlet of water flow. They fill in the fall or spring when rain or snowmelt drains into shallow depressions, and can retain water well due to non-porous soils. Seasonal pools only hold water for part of the year and experience a drying phase each year (usually in the late summer). This prevents year-round water-dependent animals such as fish from living in these habitats.
There are serious dangers for anumals that use aquatic habitats that disappear for part of the year. Yet, there are also large benefits to utilizing a habitat where fish, top predators of the larvae of other aquatic animals, are missing. In ponds or rivers, fish prey heavily on eggs and larvae, which are not very good at avoiding these predators. Without seasonal pools, some animal species would not be able to compete and reproduce.
An animal that requires a seasonal pool to survive is called a seasonal pool obligate. There are five species of amphibians and a type of crustacean that use seasonal pools almost exclusively during some stage of their life cycle. The amphibian species are:
Seasonal pool crustaceans are called fairy shrimp. A commonly encountered species in Pennsylvania is the Springtime Fairy Shrimp (Eubranchipus vernalis).
A plant species found only in seasonal pools in Pennsylvania is the northeastern bulrush (Scirpus ancistrochaetus).
Seasonal pool obligates have developed special strategies for coping with seasonally dry habitats. Some species lay their eggs in the early spring, shortly after the first spring rains. Other species lay their eggs in the dry pool bed in the fall. The eggs are tough and can survive drying out and freezing as they lie in the dry pool bed. These eggs hatch as soon as the pools fill again, getting a head start on their competition. Although they have a head start, once the eggs hatch the larvae must grow quickly. The water in their pool evaporates as spring turns to summer, and the pool gradually shrinks in size until is disappears. The larvae must transform into terrestrial adults before the pool dries up.
 It is interesting to note that eighty five percent of seasonal pool amphibians return each year to breed in the pond they were born in (Colburn, 2004). They will bypass other pools that provide suitable habitat and cross obstacles such as roads and other forms of human disturbance in order to return to the pool of their birth. This fidelity by individual amphibians to a particular pool is an important consideration when considering how to conserve the species as a whole.
There are also animals that are found in seasonal pools but do not require them for survival. They are called seasonal pool facultative species. Some examples include the Red Spotted Newt, Northern Spring Peeper, American Toad, Wood Turtle and Spotted Turtle. Seasonal pool facultative species use seasonal pools for feeding, breeding, or just a resting place on route to some other destination.
When seasonal pools dry up, species with a drought and freeze resistant life stage, usually the egg, but sometimes the larva or adult, remain in the moist soil under the leaf litter in the bottom of the pool. Terrestrial adults leave the seasonal pool and head into the surrounding landscape. Just as they need seasonal pools to reproduce and for their young to grow, the adults tend to need specific types of habitats in the uplands around the seasonal pools where they can spend the dry periods of summer and the freezing temperatures of winter. While their habitat requirements vary, one characteristic that is beneficial to all of these species is a minimum of human disturbances in seasonal pools and the surrounding upland areas.
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