A vernal pool is a specialized habitat. It is a body of water that is dry part of the year. It generally has water in the spring, hence the name vernal pool. Fish in New England have not adapted to waters that dry out during the year, so vernal pools are a place without large predators. They provide a relatively safe place for organisms that can adapt to the lack of water. Frogs and salamanders are examples of creatures that can do this. They can lay eggs in the water while it is there, and they develop to land-dwelling adults before the water dries out. The spotted salamander is common in many vernal pools. Eggs of spotted salamanders are shown here.
As in other ponds, vernal pools contain a large variety of life in a small area. The pool shown in the picture is no larger than 2 large tabletops in area, yet a remarkable diversity of life lives here. The base of the food chain is the leaf litter. Coating these leaves is a microscopic layer of algae, diatoms, and protists. These in turn provide grazing for scavengers and herbivores such as mayflies, water boatmen, and caddisflies. Also among the herbivores are a variety of crustaceans such as seed shrimp, fairy shrimp, copepods, and Daphnia. Then come predators such as the salamander larvae and the larvae of the phantom midge.
The insects are often immature and will metamorphose and fly away before the water dries. Adults are capable of flight even if they spend most of their time in the water. The crustaceans, on the other hand, are strictly aquatic. Their eggs are adapted to remain dormant in the leaf litter after the water is gone and will hatch the following winter or spring after new water has filled the pool. The microscopic creatures also go into a dormant state until the water returns.