Living in Two Worlds

The life of a vernal pool amphibian.

To everything there is a season. There is the winter time of renewal and the summer a time of growth. There is the autumn, full of harvest. And there is the springtime, the time of renewal, and the emergence of the amphibian.

Amphibians, such as frogs and salamanders, are animals that live in two worlds. Most start their lives in the depths of the water, eating algae or small invertebrates as tadpoles. Once they become adults, amphibians often spend part or all of their time on land. When they are ready, they return to the water to start the next generation.

The gift of the amphibian is its ability to live in two habitats, land and water. We can learn a lot from their adaptability and their coordination with the earth’s cycles.

This gift, however, can also be a curse. It is what makes them so sensitive to environmental change. So sensitive, in fact, that amphibians are coined "indicator species." These are species that are used as indicators of environmental distress. Scientists have been looking at species decline rates in indicator species like these for years in order to determine the health of ecosystems and the planet as a whole.   

Nothing illustrates the sensitivity and uniqueness of amphibians better than the vernal pool. Vernal pools are temporary pools of water, usually found in woodlands. In the spring, they fill with snowmelt and rain, and usually dry out completely by the late summer. Because vernal pools are dry for part of the year, they cannot support fish. This allows certain species to exist there without the pressure of fish predation. These are called obligate species, and they can exist nowhere else in nature.

According to Dr. Mike Rubbo, director of conservation science at Teatown Lake Reservation, vernal pools are “perhaps one of the most ecologically important habitats in our region, but are also the most vulnerable to change.” They are also the easiest to overlook. 

Chances are, there is a vernal pool close to you. This unassuming habitat is home to obligate species including the spotted salamander, Jefferson’s salamander, wood frog and marbled salamander. Each spring, these amphibian species loyally return to the same pools that they were born in to start a new generation. The whole food web of the vernal pool plays a significant role in the forest ecosystem and is a critical addition to the biodiversity in our area.

The trouble with vernal pools is that. because they are relatively small and are dry for part of the year, they are often not afforded the legal protection of a wetland habitat. Many local municipalities do not protect vernal pools, and many pools do not meet the 12.4-acre requirement for wetland protection under the New York State Department of Environmental Conservation. Vernal pools are easy to fill in or build over, and they often go unnoticed, especially when they are dry.

The ultrasensitive species that live in vernal pools are not affected by loss of habitat only. They are also affected by changing weather patterns. Every spring, during one of the first rainy nights where temperatures reach above 40 degrees, frogs and salamanders emerge in droves from their upland underground hibernation. They walk (or hop), in a large group, to their birth pools to meet mates and breed.

So far this spring, amphibians have emerged and deposited their eggs in vernal pools. Some amphibian eggs, such as wood frog eggs, have already hatched into tadpoles. These tadpoles will have between 6 and 10 weeks to swim around in the pools and eat as much as they can in preparation for metamorphosis, when they develop legs and walk on the land.

These amphibians are in a race against time and, in some cases, climate. This spring, because of the dry conditions, some vernal pools have already lost all of their water. In the time-span of a few weeks, hundreds of amphibian eggs have been lost. This equals the whole reproductive potential of an entire pool for an entire year.

The vernal pool habitat does not just include the area of water in the pool. It also includes the land around the pool. Adult amphibians need an upland place to go in the fall to hibernate, underground, for the winter. Vernal pools that have no upland habitat surrounding them are as harmful to a salamander as a vernal pool without water.

It is becoming more and more important for us to keep our eye on vernal pools as we continue to adjust to a changing climate. Dr. Rubbo is conducting a study at Teatown Lake Reservation to determine just how resilient the vernal pool can be in an ever-changing climate.

As temperatures continue to rise, the composition of the trees around vernal pools will gradually change. The base of the vernal pool food web is formed when leaves fall into the pool from surrounding trees. Dr. Rubbo’s study will aim to determine whether the new mix of leaf types that fall into vernal pools from a changing forest will change the ecology, and health, of the pools.

Do you have a vernal pool on your property? The best way to find out is to take a hike and try to find one. Vernal pools can vary in appearance, but look for depressions in the forest that are sometimes filled with water but dry periodically. They lack defined drainage outlets and do not contain fish. When pools are dry they still have a distinct appearance, because the leaves on the floor of the dry pool are darkened and matted down after months of being underwater.  If you have questions about the presence of a pool on your property, you can contact Teatown Lake Reservation.

How can you protect your vernal pool? You don’t have to be a scientist to protect vernal pools. Some ways to help out this fragile habitat are:

  • Avoid disturbing the pool and its upland habitat
  • Do not dump garbage, lawn clippings or organic waste into a pool
  • Keep a buffer of at least 100 feet of forested land around the vernal pool
  • Look for amphibians, but do not remove eggs, tadpoles or adult amphibians from the pool
Beth Rhines April 25, 2012 at 08:41 PM
Yes, Lisa, wood frogs in vernal pools can get VERY loud in the springtime. Its like a chorus of clucking sounds. There are other amphibians, like spring peepers, that do not require vernal pools but can often be found in them. Peepers have a high-pitched short 'peep'. Go figure :)
Don Pachner April 26, 2012 at 11:11 AM
Thank you for, Beth, your nice article about the importance of vernal pools. I am disturbed by the potential impact of odd weather patterns over the past year on the amphibian population. Case in point is a large, historic vernal pool at Mianus River Gorge Preserve in Bedford. This large vernal pool was full of water after tropical storm Irene and the snowstorm at the end of October through November. It was dry and devoid of water when I visited with a Sierra Club Earth Day nature hike last weekend; I think some serious research at this point in time could determine the impact of these bizarre weather patterns on amphibian ethology, reproduction and population demographics in our region. Is Teatown conducting any research in this area?
Denise Di Biasi April 26, 2012 at 12:17 PM
My son was about seven or eight years old when he came to the dinner table with information for my husband and I. He told us that we had a very tiny pond at the bottom of our property and that it has 'newts' (sp?) living in it. He said that we had to make sure the dogs did not go and disturb them. This 'pond' comes and goes. It is at the back end of the lower level in our yard. This area is over grown and deliberately left alone. When it rains the water table rises and so does this little, very little 'pond'. I am assuming that this is where the frogs/toads & other little creatures crawl up from.
Beth Rhines April 26, 2012 at 02:26 PM
Don, Teatown monitors the number of egg masses in our pool every spring. So far, we have not noticed any patterns of amphibian decline over time in our pools. We have had a couple seasons where pools dry up early, but in good years amphibians deposit hundreds of eggs, to ensure that there are enough 'extra' adults to buffer the bad years. A small percentage of these eggs make it to adulthood, but amphibians deposit a large amount of eggs to ensure success. Teatown will contunue to monitor pools into the future.
Beth Rhines April 26, 2012 at 02:29 PM
Denise, sounds like you may have a vernal pool on your property, or some kind of wetland area! Your son was right to want to leave it alone. It's great how children have the great gift of being able to notice things us adults overlook on a daily basis :)


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