The Three Phases of the Vernal Pool Ecosystem

The Dry Phase: Summer and Fall in the Vernal Pools

Scientists have found Fairy Shrimp eggs (called cysts) over 100 years old. When the cysts were put in water, they hatched. This cyst is seen with a special microscope that makes it look 100 times larger than normal. The Fairy Shrimp in the photo is 5 times larger than normal size.

By the beginning of summer, the soil in the bottom of the vernal pools cracks and dries. Temperatures in the Central Valley reach over 100 degrees Fahrenheit. Most of the vernal pool plants dry up and turn brown. All the aquatic life dies or leaves the pools. Although the critters are gone, they leave behind the eggs, cysts, spores and seeds that will carry the genes of their species through the long, hot summer. Each species has a way to survive the next eight months of drought. It has taken millions of years for them to adapt to live in this ecosystem. We have yet to discover the special adaptations that allow most vernal pool species to survive in this harsh environment.

Although it can look dry and barren, the grasslands and vernal pools support many species through the summer and fall. The seeds left by spring plants provide food for insects, birds, and rodents. Pocket gophers travel underground through a shallow system of burrows. They search for plant roots and bulbs, while hiding from the watchful eyes of hungry hawks and coyotes. Toads and frogs seek shelter from predators and the drying sun in these rodent burrows. Snakes slither through the dry grass poking their heads into the burrows, looking for dinner. The food web connects many species, even when this wetland isn’t wet.

Waiting for Rain

In the dryness of fall, it is hard to imagine that in a few weeks the winter rains will return. These bone-dry pools will fill up with runoff and the life cycle of hundreds of species will begin again. Vernal pools will add another year to their long history, giving us another year to investigate their many secrets.

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