Vernal Pools

It’s just near midnight on an early April evening and the dripping of the rain has finally let up while the quacking of wood frogs can still be heard in the background. We are walking along the slick black pavement, with small rivulets flowing along the roads edge – my flashlight held low, and shining ten feet ahead, slowly sweeping the width of the road, back and forth, looking for any bump in the road. Ah - there’s one! No… Just that same stick that I saw on previous passes. We meet at the half-way mark of our section and report our tallies. After recording another 2 wood frogs and 1 spotted salamander and with traffic non-existent, we decide to call it a night. 

We are part of a small group participating in an event called “Big Night”: the annual mass movement of terrestrial amphibians from their foraging grounds in the surrounding forests to their natal vernal pools for breeding. They usually move during the first rainy evening in Spring above 40F. Both salamanders and wood frogs move slowly across the roadway, sometimes stopping for minutes. We moved them across if they were in imminent danger. At this road crossing, we have seen maximums of 400 wood frogs (with approximately 20-30 casualties from cars), 32 spotted salamanders, and 6 blue-spotted salamanders on separate nights.

 

Vernal pools are unique wetland habitats that typically fill with fall and spring rains and dry out by summer. They can be as small as 100 sq ft, or as large as several acres in size, and are typically 2-3’ deep. Salamanders and wood frogs have adapted their breeding life cycle to use these pools since fish can’t survive in these conditions, providing protection for their eggs and larvae. The adults will only spend a few days in the vernal pool to mate, deposit eggs, and then head back into the surrounding woodlands. 

The most common salamander using vernal pools in Massachusetts is the spotted salamander. As adults, they are 6-10” long, as round as your finger, and a purply-brown-black color with pea size yellow spots in two rows. Their eggs are laid in fist-size clumps of up to 100 eggs, surrounded by an opaque or transparent gelatinous outer layer, and often attached to underwater plants or branches. They require that the pool does not dry out for at least 2-3 months to complete their metamorphose from an egg to larva to a juvenile salamander when they leave the water. 

Spotted Salamander and egg masses

The adult wood frogs are 2-3” and are brown with a dark eye mask. Their egg mass size is similar to salamanders but have up to 1500 eggs. The egg mass has an outside appearance of a bunch of grapes. They are also attached to underwater plant or branches and develop from an egg to larva (tadpole) and leave the water as a froglet.

Wood Frog and egg mass

In 2000, Massachusetts started a state-wide program to certify and map vernal pools by finding isolated water bodies on aerial photographs. Nearly 30,000 pools were identified. They are labeled “potential,” since it is not known if these pools contain fish or support species such as spotted salamanders, wood frogs, fairy shrimp, or a host of other species. The State not only recognized these pools as valuable environmental resources, but also the surrounding woodlands. The amphibians that develop here will travel as far as 800’ from the vernal pool into the uplands and subsequently, most return to the same pool to breed. 

Certification can be done by professionals or citizen scientists. It requires providing information on the pool location, its size, and showing evidence that obligate vernal pool species are breeding by having photographs of egg masses, larvae, or juveniles, or even audio recordings of calling wood frogs.

Certifying a Vernal Pool

This information can then be entered online at the State’s Natural Heritage and Endangered Species Program (NHESP) database, with further review by a state biologist for accuracy, and then certification if complete. 

 

Why certify the vernal pools on my land that already has a conservation restriction? 
 
There are several reasons to do this: 

• Landowner outreach – Experiencing the wonder of nature. Knowing that your land is protecting something special. Seeing the soft blue transparent salamander egg masses or a fairy shrimp swimming upside down through the pool. 

• Not all vernal pools were detected by the state mapping effort. Some of them were hidden under tree cover and others were too small, preventing identification during the aerial photograph review process. 

• Some Conservation Commissions have more stringent bylaws for certified vernal pools to not only protect them from being filled, but also protecting some of the upland habitat surrounding them to provide at least a minimal amount of uplands for them to survive.

• Observations of Jefferson or marbled salamanders should be reported to the NHESP, as land-protection efforts for these species are dependent on knowing where local populations occur.

Fairy Shrimp (< 1.5") can also be found in some Vernal Pools
(swimming upside down)

• MA-Forestry-BMP-Manual specifies: 

• No machinery can operate in a certified vernal pool at any time of the year 

• Filter strips are required for certified vernal pools. Filter strips extend 50 feet back from the bank. Within these buffer strips, no more than 50% of the basal area may be cut at any one time 

• Additional guidelines: Apply required certified vernal pool BMPs to potential vernal pools functioning as vernal pool habitat. Avoid making ruts deeper than 6 inches within 200 feet of a vernal pool. If filled with water, these can trick amphibians into laying eggs in them.