The Forest in spring:
a look into the fragile yet complex life of Vernal Pools
At first glance, this picture might not look like more than an iced over puddle. However this "puddle" is critical for amphibian populations that reside in Black Rock Forest. Vernal Pools are temporary wetlands found in forested areas that serve as breeding grounds for mole salamanders, wood frogs, fairy shrimp, and many other species. These pools typically hold water for 6-8 months out of the year and appear to be nothing more than a dried up depression on the forest floor when dry. The dry period that these pools experience is in fact very important as this distinguishes these pools from any other body of water such as a pond or reservoir. Permanent bodies of water are home to fish and other aquatic vertebrates that prey on the egg masses and the larvae of amphibians.
The light winter and lack of snow has created what seems to be an “early spring” for both the flora and fauna in the Forest. March 15th is typically referred to by herpetologists as the start of the amphibian migration in this part of the country. However the warm weather and rainy nights have triggered an early journey to the breeding grounds. Black Rock Forest staff received local reports of Spotted Salamanders (Ambystoma maculatum) crossing roadways as early as February 25th this year. It is not uncommon to see a couple of these salamanders out “jaywalking” a few weeks early, but the majority of the population has already laid their eggs in our vernal pools. Hikers often describe hearing what sounds like a flock of geese near the Swamp Trail every spring. However it’s not geese that are honking away, but in fact Wood Frogs (Lithobates sylvatica) as males congregate in vernal pools to call for potential mates. At its peak, the wood frogs will take over the vernal pool by the thousands delivering a high pitched hum of mating calls. The surface of the water is rippled and anything but calm at this time, while their calls resonate through the valleys nearby. With many different factors influencing the timing of this event, it is hard to predict when the peak will occur. However if you are lucky enough to see and hear the wood frogs calling for their mates by the thousand it is something you won’t forget.
The Vernal Fairy Shrimp (Eubranchipus vernalis) is smaller compared to the rest of creatures in our vernal pools. Measuring around ¾ of an inch, these little crustaceans are often overlooked by the average person. Vernal Fairy Shrimp reside entirely in the pool unless otherwise unintentionally distributed by other species of wildlife such as waterfowl, frogs, snakes or humans. Fairy shrimp lay their eggs in the vernal pool and after fertilization, the eggs fall to the floor of the pool and enter a period of diapause. When vernal pools dry each summer, the eggs are nestled into the debris that coats the dried up depression in the forest. Contrary to most other species that inhabit the vernal pool, the dry period is especially important for the shrimp. Some pools that don’t experience a dry period will often show no sign of Vernal Fairy Shrimp life, however the following year when the pool fills, it will be teaming with life. The fairy shrimp hatch shortly after the pools thaw from winter ice and begin the egg producing and laying processes all over again. It is believed that adult fairy shrimp only live for several weeks before water temperatures reach about 60 degrees and mole salamander larvae begin to feed on the shrimp. This little crustacean has quite a complex life cycle, with most people completely unaware of their existence.
Additionally it is extremely important to keep out of these fragile areas, even when they are dry during the summer months. Many of the species that inhabit the pools breathe through their skin, transferring every pollutant directly into their body. Please do not wade or allow your pets to wade through these pools. This is another reason why we require all dogs to be leashed and under your control at all times.
- Aaron Culotta
Black Rock Forest
P.S. For more information:
For great additional detail regarding the importance of vernal pools, check out this wonderful article, "Out There: Big Night" in the Highlands Current (a Philipstown newspaper) about local volunteers assisting amphibians crossing roadways to reach Vernal Pools in the spring.