By Keith Williams, Lancaster Conservancy Vice President of Engagement & Education
Vernal pool. Photo by Keith WilliamsThe stream at Climbers Run Nature Center used to take a different path, and the remnants are still carved into the landscape. The river’s former course is dry and obvious if you know what to look for, and there are two deeper spots in the old channel that temporarily hold water that accumulated during the winter through the spring and early summer. These used to be deeper holes in the stream when it flowed here. They are only 10 feet by 10 feet, but they served important habitat roles in their constantly submerged form despite their relatively small size. Deeper holes provide thermal refuge for fish in the hot months of summer, and better cover from aerial predators — and now they are critical habitats as vernal pools.
Vernal pools, literally spring pools, are shallow depressions that contain water for just part of the year, usually around spring – hence the name vernal. Their relatively small size contributes to the ephemerality of the water they contain, and the fact that they are temporarily wet is an important feature.
Pickerel frog. Photo by Kerry Givens
Amphibians require water to complete their life cycles. Male and female frogs, toads, and salamanders move from the terrestrial ecosystem where they spend their adult lives into the aquatic to mate. Their fertilized eggs hatch into larvae and tadpoles that are entirely aquatic. They use gills to extract dissolved oxygen from the water and have tails to swim. Over time, lungs take over for gills, and they become air-breathing as their tails are absorbed and their legs grow.
Larval amphibians are easy prey for fish, so if they are born into aquatic ecosystems full of fish, their chances of survival are slim. Water bodies that dry out for part of the year can’t support fish populations, so the predatory threat to young amphibians in these temporary wetlands is significantly less than the predatory pressure in wetlands that retain water year-round.
Adults preferentially seek vernal pools for mating to increase the chances of success for their babies. But if the vernal pool they choose is too temporary and the water dries before their babies develop lungs and legs, they die. These amphibians need just the right amount of water that lasts for just the right amount of time. These small temporary habitats are just what amphibians need to successfully bring the next generation into existence.
Amphibians are the most threatened vertebrate class of organisms on the planet with 41% of species threatened with extinction, according to the International Union for Conservation of Nature. When viewed through this lens, these small and temporary habitats become even more important.
Clusters of frog eggs. Photo by Keith Williams
One vernal pool at Climbers Run Nature Center is full of wood frog egg masses in early spring. The adults have already come and gone, and the forest feels empty without their loud rumpus. Soon the spring peepers will fill the acoustic void with the high-pitched chirps of males attracting females.
There are gelatinous salamander egg masses in another nearby vernal pool – likely tiger, marbled, or spotted salamanders. These are our largest terrestrial salamanders at 6 to 8 inches long with robust bodies. They are cryptic and spend most of their lives in shallow mouse burrows or under leaf litter. They are declining in parts of their range, so their dependance on and presence in these vernal pools is especially acute.
Vernal pools may be small and temporary, but small and temporary does not mean unimportant.
When we look at humans from a deep time cosmological perspective, we too are small and temporary, not even a blink in the eye of the universe. Modern humans have only been here for 200,000 years of the universe’s 13.7-billion-year history. And yet, what we do now will have significant and lasting effects on this planet, and on our local ecology. Protecting these small and temporary places is an example. All the life that depends on one 10-by-10-foot pool would be gone if it weren’t for the Conservancy’s work to forever conserve these spots. Collectively, we can make significant and lasting contributions to future generations of both humans and wildlife.
