As you head to the woods seeking relief from late winter cabin fever, you're virtually certain to stumble upon vernal pools - small bodies of water that collect in depressions in the landscape. Melting snow and late winter rains fill these shallow depressions, which can be as small as a kiddy swimming pool to an acre in size. But they must be shallow, and they must, at some point in late spring or summer, dry up completely.
Vernal pools are about to explode with life. As days get longer and daytime temperatures flirt with the 50s, aquatic invertebrates that have been dormant for months and amphibians waking from hibernation return to their birth ponds to reproduce. Wood ducks visit to loaf and feed.
Eggs of aquatic insects and crustaceans hatch to form the base of the food chain. In February, wood frogs, whose frozen bodies have been frog-cicles all winter long, find their way to snow-ringed pools. These are the small brown frogs marked by a raccoon-like facial mask. Males sing their duck-like calls to attract females. By mid-March, male spring peepers serenade females to entice them to the pools. In April, American toads trill their song of procreation at the water's edge.
Perhaps the most impressive visitor to vernal pools are never heard and seldom seen. Spotted salamanders spend most of their lives in underground burrows, but on rainy late winter nights they surface and return to their natal vernal pools to breed. At some locations these mass migrations can number in the hundreds or even thousands. Sometimes these salamanders can be observed en masse crossing highways that separate their terrestrial habitat from the vernal pools.
Spotted salamanders are easily recognized. They are dark with two rows of yellow spots running the length of the body and can reach a length of eight inches. To find spotted salamanders, curious naturalists must get outside on rainy, late winter nights. It means wearing raingear and getting wet feet. The reward can be seeing masses of salamanders writhing in vernal pools.
After finding a breeding pool, visit after dark, during the rain, and when the temperature is above 40 degrees. Use a flashlight to scan the pool. The rain allows the salamanders to stay moist during their brief journey above ground.
Males arrive at pools hours or a few days before females. When the females arrive, they "dance." Males and females swim in circles and rub against each other. Eventually males deposit a spermatophore (a packet of sperm) on a piece of vegetation. A female then picks up the spermatophore with her cloacal lips, and eggs are fertilized as they pass through the cloaca. As many as 200 eggs form a gelatinous mass that can be as large as a baseball. The eggs hatch in 30 to 60 days, depending on temperature. The carnivorous larval salamanders live for two to four months before transforming into adults and then migrating back to terrestrial habitat. As larva, these salamanders eat a variety of aquatic invertebrates.
The value of vernal pools to breeding amphibians is clear. Because these wetlands dry up completely at some point later in the year, they cannot support populations of fish. And since fish are major predators of aquatic invertebrates, amphibian eggs, tadpoles and larval salamanders, vernal pools are a relatively predator-free habitat. This means breeding success will be high.
On the other hand, using this predator-free habitat means betting that eggs will hatch and larva will transform into terrestrial adult forms before the pools dry up. During dry years, salamanders and other inhabitants of vernal pools fail to grow their populations because their eggs and larva die when pools disappear. So wet springs are great for the creatures of vernal pools; dry springs mean population growth must wait until next year.
Ephemeral wetlands can be difficult to identify and protect simply because they are ephemeral. Logging operations that do not leave buffer zones around vernal pools increase their drying rate, and land development can destroy these pools completely.
Vernal pools are not just mud holes in the woods. They are thriving communities of aquatic organisms perfectly adapted to these specialized ephemeral habitats.
- Send questions and comments to Scott Shalaway, RD 5, Cameron, WV 26033 or his website, scottshalaway.googlepages.com