In the state of Michigan, vernal pools are critical for the reproductive success of natal amphibian and insect species. These seasonal wetlands, devoid of fish, provide the perfect habitat for breeding frogs, toads, and salamanders. Vernal pools are composed of shallow depressions that only contain water for part of the year – usually in the early spring.
Because these pools only contain water for part of the year, predatory fish species cannot establish permanent populations, which is critically important for invertebrate species reproduction. Often occurring in grasslands or forests, vernal ponds are accessible to a variety of breeding amphibian species such as the tiger salamander (Ambystoma tigrinum), spotted salamander (Ambystoma maculatum), blue-spotted salamander (Ambystoma laterale), and wood frog (Lithobates sylvaticus). Water quality and chemistry play a large part in what particular species can thrive in individual ponds.
To determine a seasonal wetland’s health, land managers conduct vernal pond surveys. Every spring, before the period of summer drought and when the ponds are teaming with life, these pools are surveyed for specific indicator species. An indicator species is one that tells biologists if an ecosystem is healthy or not. Oftentimes the most “picky” when it comes to livable environmental conditions, these species indicate that an ecosystem is thriving if they are present.
Throughout the month of March, I was fortunate enough to go along on some of these vernal pond surveys. Equipped with waders, nets, and headlamps, every night from about 8:30pm – 11:30pm we herped. “Herping” is the informal biological verb for “searching for amphibians or reptiles”.
Herping at night is preferred, as it is easier to spotlight salamanders and egg masses in all of the muck and leaf litter at the bottom of a pond without the sun’s reflection and glare. Another reason that surveying is done at night is because this is when frogs and toads are at their loudest – and identifying a frog by their call is just as important as finding and seeing one with your own two eyes.
Wood Frog (Lithobates sylvaticus)
The four main indicator species that we looked for were wood frogs, spotted salamanders, blue-spotted salamanders, and fairy shrimp. While fairy shrimp don’t necessarily fall under the herptiles category, they are important invertebrates that also use vernal pools for reproduction.
Fairy shrimp are crustaceans that live a short life cycle solely in seasonal wetlands. Vernal pool fairy shrimp are federally threatened, so finding this species in local ponds is of utmost interest to conservation groups. We did not find any fairy shrimp when I was out with surveyors but finding three of the other indicator species implies that fairy shrimp would also thrive there.
Spotted Salamander (Ambystoma maculatum)
Surveying vernal pools is important to not only measure the health of an ecosystem, but also the health of our amphibian populations. Amphibians are critical to the environment, and also science as a whole. Amphibians have a lot to teach us about evolutionary processes, and survivability in extreme environments.
Amphibians have been around for over 350 million years and have survived dinosaurs, meteors, pollution, and humans alike. Amphibians are also integral prey and predator species in the food web; controlling insect populations and providing a food source for larger predators like birds and opossums. Aside from all of the above, amphibian and invertebrate species are a beautiful piece to our diverse ecosystems, and it is up to us to ensure that they continue to thrive.
