Welcome to the exciting world of VERNAL POOLS!!!

    Vernal pools  are fascinating and dynamic environments possessing a great deal of mystery and appeal.  While some claim that they are exclusively Californian, others say that a northeastern habitat.  In fact, they occur in both regions, although a vernal pool in New England might be unrecognizable to a Californian, and vice versa.  Actually, there are similar formations in other countries, including Africa and South America.  Nonetheless, vernal pools are a rarity, of sorts- unique in each region in which they occur.  This web page provides a brief overview of New England vernal pools and the creatures which inhabit them.

        Occurring in disparate regions with distinctly different climates, vernal pools are highly variable, making them difficult to define.  There are three key elements which must be covered in any definition: 1) vernal pools are temporary ponds which dry up seasonally,  2) vernal pools are not inhabited by fish, and 3) vernal pools contain certain species which occur nowhere else, or which require these temporary ponds for breeding.

    Vernal pools  are essentially isolated depressions, generally found in wooded areas, which range in size from a large puddle to a small pond.  These depressions are filled with water each spring when the snow melts, although rising groundwater may also provide a source of water.  This water generally dries up late in the summer, filling again in the fall, although deviations from this pattern are not unusual.

        This drying prevents the successful establishment of breeding populations of fish.  The absence of fish is an important characteristic of vernal pools, because fish have proven to be voracious predators of many vernal pool species; fish populations would preclude a healthy vernal pool community.   Shallow water and insufficient oxygen may deter the establishment of fish populations when water persists through the year (as it may, on occasion).

        There are some species which exist exclusively in vernal pools, such as fairy shrimp, and other species for which vernal pools provide essential breeding grounds.  These amphibians may spend most of there lives elsewhere, however the species would not persist without vernal pools in which to breed.  The presence any of these obligate species generally indicates vernal pool "status".

VERNAL POOL CREATURES

Fairy Shrimp

        The presence of fairy shrimp establishes, without a doubt, the existence of a vernal pool.  These delicate and beautiful creatures live out their entire life cycles in vernal pools and can be found nowhere else.  Although there are a number ofdifferent species of fairy shrimp, distinguishing them is difficult.  They can be a variety of colors, ranging from blue-green to pale orange and they grow between .5'' and 1'' long.   These small, graceful filter-feeders swim on their backs with their numerous legs fanning rhythmical above them.
 
        Difficult to observe because of their small size, the best way to see these creatures is to run a net through the water and empty the contents into a large glass jar (be sure to put them back when you are done!).  Upon closer examination, modified antennae can be seen on the males which are used for grasping the females when mating.  The females may carry egg sacks.  Fairy shrimp mate and die by late spring.   Eggs fall to the bottom of the pool to hatch and begin the cycle over again next season.

Amphibians

        Observing vernal pool amphibians is most easily accomplished in the early spring when most of them are migrating to their breeding grounds in large numbers.  Although a certain amount of determination is required in order to witness this phenomena, it is truly a spectacular event.   It usually begins on the first warmish (over 40 degrees F), rainy night in late winter or early spring.  Get your umbrella and your flashlight and head into the woods to your nearest vernal pool and prepare yourself for a wild spectacle.  If you don't know where any pools are, they can often be located at this time simply by listening for the sound of calling wood frogs, or by driving slowly and watching for spotted salamanders crossing the road in your headlights (carefully!).

Wood Frogs     Rana sylvatica

        These are the most vocal of vernal pool inhabitants, and the strange, duck-like   quacking  of amorous males creates quite a din on rainy spring evenings.  Wood frogs are petite (2'' to 3''), usually pale brown frogs which always possess a distinctive, dark mask around their eyes.  Smaller than the females, the males possess pads on their thumbs during mating season for gripping the females.  Females can be quite a bit larger, especially when they are carrying eggs, and are often paler and reddish in color.
        At this time of year, males will attempt to clasp and mate with almost anything that moves.  In order to avoid confusion, males have a characteristic "release" call which can be heard when they are clasped by other males.  If you catch a male wood frog and clasp him gently behind his front legs, you may hear this call.  This is different from the mating call, given only in water, which sounds remarkably like a quacking duck.  The male clasps the female behind her front legs, fertilizing the hundreds of eggs which she lays.  The pair may remain clasped together (in "amplexus") for anywhere from a few hours to several days!!  Breeding activities may last only a couple of weeks, after which the frogs leave the pond and head for the woods.  If you miss the frogs, it is not difficult to observe the huge masses of jelly-like eggs which are left behind.  Several days after they have been laid, a greenish tint appears, due to the growth of a symbiotic algae.  Eggs usually hatch within two to three weeks.  After about two months, juvenile wood frogs emerge from the pool.  Wood frogs take refuge under logs, leaf litter and in shallow burrows during winter months.

Click here  for more fun and interesting information on frogs.

Mole salamanders        Ambystomatidae

        There are several species of mole salamanders which may be found in the vernal pools of New England.  They are all stout creatures which spend most of their time under the ground and require vernal pools for breeding.  Larval stages  of the lives of these creatures occur exclusively in vernal pools.

Spotted salamanders      Ambystoma maculatum

        Spotted salamanders are probably the most common and easily observed of the mole salamanders in the area.  These plump, glossy creatures are black with striking yellow spots distributed randomly on their head, back, and legs.  Rarely, the spots on the head will be orange.

        Males will appear first, and gather into groups called "congresses" to await the arrival of the females.  They may end up waiting for a couple of days if warm, rainy conditions do not persist.   With the arrival of the females, courtship commences.  A pair will circle around each other with a great deal of nudging.  The male will rub his chin along the female's back to stimulate her.  Eventually, he will move away from the female and deposit a small, white spermatophore (which contains sperm) in front of her.  The female will walk forward and pick up the spermatophore with her cloaca for internal fertilization.

        A couple of days later, the female will deposit her eggs on twigs in spherical lumps of up to 250 eggs.  These eggs will swell to softball size, and the protective jelly coating which covers them may be completely clear or it may have a milky, white hue.  The eggs will hatch in four to eight weeks and the resulting larvae are usually ready to leave the pool in one to four months, although some have been observed to overwinter under the ice.  These juveniles will spend up to three years under the ground, until they are ready to begin life as sexually mature adults.

Blue spotted salamanders     Ambystoma laterale

        Blue spotted salamanders and the very similar Jefferson salamander both occur in New England and are quite difficult to distinguish.   Further complicating matters, these two species have been known to hybridize, resulting in the Jefferson-blue spot complex.  Jefferson-blue spots are almost exclusively female, and are believed by many to reproduce by parthenogenesis.   This means that the female can actually produce fertile eggs on her own.
 
        Species identification depends largely upon the geographical location of the animal.  Blue spots are northern creatures, found in Canada and northern Minnesota, Jeffersons occur in Massachusetts, southern New York, and south, and everything in between is likely to be a complex.   Blue spotted salamanders are generally smaller than Jeffersons, at approximately 5''.  They are greyish-black in color, with small blue flecking.  Jefferson salamanders also tend to have longer toes.

Marbled Salamanders     Ambystoma opacum

        The marbled salamander has a black belly with distinctive white bands down its neck, back and tail.  It grows only 3.5'' to 4.5'', giving it an even stockier appearance than the other mole salamanders.  The white bands on females tend to be greyish, allowing for easy identification of the sexes.
 
        Marbled salamanders are different from other members of the Ambystomatidae  family in their mating habits.  Aside from being somewhat more elusive and mysterious, marbled salamanders migrate to vernal pools in the autumn instead of the spring.  At this time, the pools are dry and courtship (which is seldom witnessed in A. opacum) takes place on dry land.  Aside from this major difference, courtship rituals are rather similar to those of the spotted salamander.

        After mating, the female digs a shallow burrow and lays up to 200 eggs in it.  Highly unusual, the female remains with the eggs, defending them fiercely from predation and protecting them from dessication.  She will leave the eggs after rainfall begins to inundate the area.  The eggs hatch within a few days of inundation, sometimes overwintering under the snow and hatching the following spring.  The larval stage lasts approximately five months and the adult lifespan of this short-lived species is only about five years.

Vernal pools are fascinating systems which offer a great deal of excitement and entertainment to the observer.  These areas provide essential habitat to numerous mysterious creatures which spend much of their lives underground.   There is still a great deal to be learned about many of these animals.
        Unfortunately, vernal pools are often not recognized as wetlands because they are completely dry for much of the year.  This may mean that they do not recieve the sorely-needed protection which they are "legally" gauranteed.  Many inventive approaches have been taken in various states in order to protect vernal pools.  The first step in their protection is educating people about vernal pools so that they will be recognized, appreciated, and preserved.

REFERENCES

Conant, R. & J. Collins, 1991. Peterson Field Guides: Reptiles and Amphibians. Houghton Mifflin Company, Boston.

Robinson, R., 1986. Rings of Flowers. Bioscience. 36:6(3).

Tyning, T., 1990. Stokes Nature Guides: A Guide to Amphibians and Reptiles. Little, Brown & Co., Boston.

Created by Maire Cotter-Brown at Antioch New England Graduate School
Questions or comments are welcome: maire@igc.apc.org
NOTE: This web page is an independent creation and the information and opinions expressed within it do not necessarily reflect the opinions of the host.