Saturday, on a near 50-degree sunny morning, I joined a guided walk led by MassAudubon to explore the vernal pools at Ashumet Holly in Falmouth.  A vernal pool is a unique temporary wetland that fills with water in the autumn or winter due to rainfall, snow melt and rising groundwater and remains ponded through the spring and sometimes into early summer.  What makes vernal pools different from an ordinary pond is that vernal pools dry completely by the middle or the end of summer, preventing fish from establishing permanent populations.  The absence of fish is critical to the reproductive success of many amphibian and invertebrate species that rely the absence of these predators to breed.

Although we did not find any fairy shrimp in the four ponds we investigated, the organizer had a fairy shrimp (Eubranchipus vernalis) in a small container for us to see.  Reminiscent of a large sea monkey, this species of fairy shrimp is a freshwater crustacean that specializes in vernal pool life, and is considered an indicator species of vernal pools in Massachusetts.  These 1/2 inch to 1 1/2 inch long creatures have stalked compound eyes, two sets of antennae, and 11 pairs of swimming legs (see photo below).  One of the fairy shrimp’s unique adaptations to survival in a temporary pond is that their eggs can survive in the mud and dry out with the pool, hatching the following year in the spring when the pools refills.  Additionally, although this dormant period typically only lasts between 6 to 10 months, eggs have been successfully hatched in a laboratory after 15 years.  This means that if there are a number of successive dry years, fairy shrimp can still re-emerge years later when conditions are right.

The spotted salamander (Ambystoma maculatum) is a mole salamander common to the eastern United States. This relatively large salamander can grow up to 9 inches long, and has distinctive yellow spots (see photo below).  “Mole salamander” refers to the fact that these animals spend most of their life underground, coming to the surface only to forage after a rain or to breed in the spring.  Spotted salamanders are one of the many amphibian species that rely on the fish (i.e. predator) free vernal pools to reproduce. Spotted salamanders produce large jelly-like egg masses of 100 or more eggs and attach them to grasses or branches in the pool.  An example of a spotted salamander egg mass is shown in the photo below.

Another vernal pool species that most people hear, but few get to see, is the spring peeper (Pseudacris crucifer).  This relatively small brown tree frog gathers in and around vernal pools this time of year making loud, high-pitched peeping call to attract mates.  The faster and louder the males sing, the greater their chances are of attracting a mate.  Although peepers often have a distinctive “X” marking on their backs, the individual we found (pictured below) was a dark enough brown that the “X” was obscured.

One final vernal pool amphibian that we were unable to find at Ashumet Holly that morning, despite MassAudubon’s ongoing re-introduction effort, was the eastern spadefoot toad (Scaphiopus holbrookii).  Although they are relatively common throughout much of their range, they are listed as threatened in Massachusetts due to heavy development and wetland loss.  The spadefoot toad can grow up to 3 inches long, range from yellow to brown in color, and has a unique vertically oriented pupil.  Like the spotted salamander, the spadefoot toad spends most of it’s life underground, emerging only in the spring to congregate at vernal pools to breed.  They are well adapted for burrowing, and the “spadefoot” name refers to a hardened black “spade” on their rear feet, which help them dig (see bottom photo).