🐸 Ephemeral Living » Vernal Pool Explorations

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☆ Understand » The Importance of Vernal Pools

Vernal pools can occur almost anywhere—in forests, fields, shrub swamps, marshes, or in gravel pits. They can be smaller than a tenth of an acre or larger than two acres. Essentially, vernal pools are wetlands that are or become isolated while containing water, are utilized by indicator species, and have wet-dry cycles that preclude permanent populations of fish ^[KL09]. In the Northeastern United States, these pools are most visible during the springtime. They are usually found in a natural or man-made depression that lacks a permanent outflow.

Due to their seasonal nature, vernal pools are not suitable for fish life. In permanent pools, rivers, and lakes, fish act as a predator for many invertebrate species and sometimes even prey upon eggs of amphibian species. Without fish predation, vernal pools serve as optimal breeding sites for a number of species, especially amphibians ^{([GJ93],[KL09])}. These amphibians usually spend the majority of their life cycle in adjacent uplands or even wetlands. Vernal pools are critical to the maintenance of the viable populations of these amphibians ^{([SJ00],[PE00])}.

Vernal pools are important for biodiversity, both locally and globally. For a species with a narrow distribution, a particular vernal pool might be the only place on earth where that animal is found. If that pool gets destroyed, then the species will get extinct. For a species with a broad distribution, individual vernal pools are essential for sustaining their local populations. The elimination of these pools might result in the extinction of that species in a particular area. For example, in Massachusetts, the delicate yet complex Fairy shrimp is known to a small number of pools, and the Spadefoot toad is known to be present only in 40 sites in the entire state.

Vernal pools serve as an important water source for all kinds of wildlife. They also make exceptional corridors in the overland passage of various amphibians and reptiles as they move from one wetland to another ^[KL09].

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▹ Vernal Pool (Wiki)

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☆ Know » Pool Key Species

Since there are no breeding populations of fish (mainly because of low oxygen level and periodic drying), vernal pools provide a safe environment for numerous amphibians and other species.

Among those species, some vertebrate and invertebrate species are totally dependent upon vernal pools for all or a portion of their lifecycle. Such animals are known as “obligate” or “direct indicator” species of vernal pools.

Other species might use vernal pools for various activities in their lifecycle but not all, and are able to successfully complete their life in other types of wetland habitats (such as permanent pools). Such species are called “facultative” vernal pool species (also known as “indirect indicators”).

In Massachusetts, for example, the vernal pool obligate species are the wood frog, the spadefoot toad, four species of salamanders (the spotted salamander, the blue-spotted salamander, the Jefferson salamander, and the marbled salamander), and two species of fairy shrimp. The facultative species include most of the other remaining frogs, few reptiles, fingernail clams, amphibious snails, insect larvae (dragonfly, damselfly, caddisfly larvae), and leeches. 

Discussion » What are some special strategies that vernal pools species use?

☒ Due to the seasonal nature of the pools, both animals and plants living there have some adaptation to help them survive in these challenging environments. There are three basic types of strategies:

- get off to a fast start,
- mature early or rapidly,
- live a prolonged period of time without water.

☒ Some amphibian species (e.g. wood frogs, mole salamanders) travel to vernal pools to lay their eggs shortly after the first spring showers. Other species, such as the fairy shrimp, leave eggs at the bottom of the pool, which can withstand drying out in the summer and even freezing in the winter.

☒ The larvae of vernal pool invertebrates and amphibians race against time and must grow quickly once they hatch from the egg in spring. As spring turns into summer, water evaporates and the pools gradually shrink in size and sometimes may disappear altogether. The larvae must then transform into their terrestrial adult selves before the pools dry up.

☒ For reasons yet unknown, an estimated 85% of the obligate amphibians return each year to breed in birth-pool, dismissing other suitable pools and navigating through man-made obstacles like roads, construction sites, golf courses, and other forms of human disturbances ^[CE04]. Note that 'site fidelity' for some of the species of vernal pools is a critical consideration when determining the protection of a species as a whole.

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▹ Amazing Animals that Use Vernal Pools

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☆ Track & Observe » Safe Pool Explorations

Before visiting a vernal pool, make sure to have read first both the EwA Wetland Etiquette and the EwA Casual Herping Rules so as to minimize your ecological footprint and disturbance in these fragile habitats.

Finding a Pool

First things first. For exploring a pool, well... you need a pool!

It is actually not too hard to find one. There may be one right in your backyard, or somewhere out of view on your property. Or maybe you spotted one while hiking, biking or walking in a wilderness area.

In the winter, when the pools are dry, they can sometimes be identified by the presence of dark, matted leaves within a depression in the ground. 

Here are a few characteristics that may help you notice dry pools ^[MM16]:

• Check for a flat topography with variability, especially depressions in the landscape. Areas with several or a chain of depressions have increased value as vernal pool habitat.

• Evidence of vernal pool hydrology:

1. Leaves darkened by water stains or a film of sediment. You may need to brush away recently fallen leaves to reveal the stained layer
2. Siltation marks or water stains on surrounding trees or vegetation
3. Trees with buttressed or stilt roots
4. Sphagnum moss around the edge of a depression
5. Wetland plants growing in a dry depression

Some pools refill in fall or early winter from groundwater or rainfall. Pools may be evident from a distance in a leafless landscape. Look for pools in late fall and into winter prior to significant snowfall. The silvery sheen of a frozen pool surface may indicate a vernal pool. Note the location of these pools for a spring follow-up visit.

If you don't know of any pools, then areas marked as wetlands on the topographic maps are good places to start.

For instance, below is a map of an area and its pond where we spend a lot of time monitoring phenology and mapping biodiversity.  The little blue plant icons (2 sets of them) on the map indicate wet areas (other than the obvious pond), and we can count here 5 certified vernal pools (5 blue crosses).

Wherever you live, you can search the internet with keywords such as ‘vernal pool’ ‘map’. For instance, in Massachusetts, where we run live vernal pool events, such a search returns multiple hits including the Natural Heritage Endangered Species Programs (NHESP) Massachusetts Aerial Photo Survey which indicates potential Potential Vernal Pools locations. You can also check with your local conservation commission for information about the known pools which are on public land.

Exploring the Pool

So, you found a pool, and -say- you know it's not certified. Then, is that pool that you're looking at indeed a vernal pool? That's where 'investigation' comes into the picture. 

After finding a potential vernal pool, record the date, time of the day, and the exact location of the pool (you can use Google map or other GPS phone app or device). Since vernal pools change seasonally, that kind of information will help you find that pool again throughout the seasons to experience the natural cycle of these wonderful habitats.

☒ Describe the habitat in your own words.

Is it an isolated body of water? Vernal pools are almost always completely or partially surrounded by forests, woodlands, or savannas ^[CE04]. This characteristic sets them apart from pools in open landscapes which harbor species of emergent marsh, wet meadow, wet prairie, and so forth.

Try to measure the pool area using a measuring tape.“A picture is worth a thousand words” Take detailed photographs (if the vernal pool is large, take a panorama or multiple shots from different angles).

This kind of data is useful when sharing information on social platforms such as iNaturalist, or when certifying the pool so as to have it protected.

☒ Explore the Critters!

This is the fun part. A small net is perfect to capture invertebrates and vertebrate larvae. Swipe your net through the water randomly (yet cautiously and following proper herping etiquette so as to avoid harming any of the critter and hidden wildlife). Dump slowly the content in your shallow container along with some water.

Interestingly, you will find various critters by netting at the water surface (e.g. fairy shrimps, water striders, mosquito larvae, backswimmers, water boatman etc.) and in the leaf litter (e.g. chironomid midge, mayfly larvae, daphnia etc.)

 

Take notes, draw a rough sketch and take photographs of the specimen you're describing. Use a ruler for scale reference (as shown in the salamander pic above). After observation, make sure to return them to the pool along with the water (again following proper herping etiquette).

☒ Watch out for egg masses

Amphibian egg masses can be found by looking for them at the water surface or attached to vegetation or fallen logs below the surface.

You can cast a shadow on the surface to eliminate reflections (or wear polarized sunglasses). Using a hand lens help having a better view of the masses. Do not remove the egg masses from their attachment sites. Never ever transfer egg masses between pools.

Again, take notes, make a rough sketch and take photographs.  

☒ Remain alert -all your senses open

Depending on the time of the year, you might hear the mating chorus of wood frogs or the loud peeping of the spring peeper. Record your auditory observation with your phone.

The smell of the mucky soil in those pools is quite unique and part of the experience too! Describe your olfactory experience for future references. 

Beware of deep water, muddy bottom pools, submerged objects, and drop-offs.

Have the lowest impact possible, and always keep in mind how fragile the vernal pool ecosystem is. A recent study found that widely used repellents are lethal for salamanders. Do not wear DEET and any harmful chemicals that make most of the insect repellents and sunscreen if you intend to enter the water and sample. Never enter a pool wearing clothes or shoes that are coated with permethrin. Permethrin equates to death for many pool species. Have someone ponding for you (and don't touch any critter), or plan to come back later free of those chemicals. The pool inhabitants will thank you!

☒ Share your findings

At the end of the activity, gather together in a quiet place, take out your notes and share your experience and findings with your team members. Use your hands-on experience to educate others, your friends and family, neighbors, schools, and the community.

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▹ EwA's Casual Herping Rules