Earlier this year in April, my wife and I took part in a Vernal Pool volunteer training workshop that enlists citizen scientists to help a monitoring program underway by Michigan State University and the Michigan Natural Features Inventory (MNFI).  This was, in part, inspired by the woodlands around our neighborhood that frequently have temporary pools throughout the year.   I have photographed around them for years, but didn’t know much about them as complete ecosystems.  Many people probably just see them as small ponds, or even puddles — and more likely as mosquito breeding grounds.  They don’t realize the changes they undergo throughout the year.  So this workshop and enlistment in the volunteer work is an effort to learn more about their importance and the wildlife that depend on them.

I waited until this time of the year to post about this as it marks the completion of my 3 required surveys for this season.   I wanted to have the perspective from start to finish for at least one season.

Why Vernal Pools are important

A vernal pool is defined as a small, shallow depression that contains water for only part of the year.   They are a type of wetland that fills between late fall and spring, then ends up dry or mostly dry by late summer.   Occasionally they will contain water throughout the year in very wet seasons, but to be defined as vernal, they eventually need to temporarily dry up.   This is particularly important to some key species that inhabit them, which I’ll describe in the next paragraphs.   It is also why vernal pools do not support any breeding fish populations because they eventually run out of water.   This lack of fish is also key to the survival of the indicator species in vernal pools.

In Michigan, as of today, wetlands are only subject to protections by state law if the area is more than 5 acres, within 500 feet of a lake or stream, or 1000 feet to a Great Lake.   Nationwide in the US and worldwide, of course, wetlands are recognized for their critical importance to surrounding water quality, climate, and ecosystems.   Vernal pools, though a type of wetland, typically being much smaller, are not offered any of these protections in Michigan.   As such, their cyclical nature and changing use by a variety of species may result in a failure to be identified.   This spells trouble in preserving these key habitats from development.   And, of course, climate change is playing a key role on vernal pools by impacting rainfall patterns, snow accumulations, and drought periods.

Vernal Pool Indicator Species

Many of the species that live in, and rely upon, vernal pools, have evolved in ways to create adaptations to the pool’s variable and temporary nature.   The species that depend on vernal pools are called indicator species.   They utilize these habitats for the reproduction and development of their young and rely upon a lack of fish predators.   Indicator species may vary from region to region.   In Michigan, there are four:

• Wood frog (Rana sylvatica)
• Spotted salamander (Ambystoma maculatum)
• Blue-spotted salamander (Ambystoma laterale)
• Fairy shrimp (Branchiopoda or Anostraca)

This doesn’t mean these are the only species found in vernal pools, far from it.    Vernal pools are vibrant examples of biodiversity and provide vital support the surrounding food chain.   It just means these particular species have evolved in a way that their life cycle exploits this temporary wetland that is free of fish.   These pools are known to be key habitats in support of rare Michigan species such as the small-mouthed salamander, blandings and spotted turtles.

With the exception of the fairy shrimp, the wood frogs and salamanders can breed in other wetland environments.  However, their survival rate is much better where their eggs and young do not have the threat of fish.   With amphibians in worldwide decline, their survival depends on the most favorable conditions possible.  

Fairy shrimp can only occur in waters that are free of fish.   Their eggs actually require drying, flooding, and potentially freezing to hatch in a process called cryptobiosis.   Many people may remember ads for “sea-monkeys” in the back of magazines or comic books.  Those are hybridized brine shrimp.  Fairy shrimp are similar because their eggs can completely dry out or freeze, and then hatch in water. The shrimp play a vital role in these habitats.  They are important in the food chain and filter bacteria, phytoplankton, and detritus.  Fairy shrimp are also a sensitive indicator of water quality and a key identifier of a vernal pool.   If there are fairy shrimp there, it is certainly a vernal pool.

Below is a video of a fairy shrimp we collected during our workshop.   It’s size was about the width of a fingernail.   As this was just a general pool sampling, you can see there are a lot of other “critters” swimming around in there also.   I would invite anyone to do this in a pond near your house with a white container.  You will be amazed at the amount of life present.  Each species playing their role in the ecosystem.

Enter Citizen Scientists

The challenge in Michigan right now is accumulating the data and resources to work on vernal pools.   A Vernal Pools Work Group was formed in 2011 to develop an approach to studying them statewide.  This group consists of a cross-functional team of state ecological experts and others wishing to be involved in vernal pool conservation efforts.   Key objectives were to identify conservation needs, evaluate mapping methodologies, and develop a volunteer program, to name a few.   The training program I attended was an outcome of the efforts of this work group.   It was a very well done 6-hour workshop put on by the leaders of this effort; Yu Man Lee, Daria Hyde, & Phyllis Higman with support by David Clipner of the Leslie Science and Nature Center in Ann Arbor, Michigan.

Once you learn about vernal pools and the variety of species you are likely to encounter, you are taken out in the field to put those identification skills into practice at an existing vernal pool. While I have occasionally encountered salamanders and wood frogs while out photographing, I never knew much about the fairy shrimp that inhabit these critical freshwater pools.   Let me tell you, it was like being a kid all over again discovering some new, little critter in the woods.

An objective of the training is to have people qualified to begin their own monitoring of vernal pools in their own areas, map them out, and contribute to the overall data resource on pools throughout the state.   As I mentioned in the intro, a volunteer’s effort involves mapping out and visiting your monitored sites 3 times a year (early spring, late spring, and late summer).   This is to document how the pool is changing, documenting the species that are there, particularly the indicator species.   Ideally, this will lead to better protections than they have now when fed into a central collection site for all Michigan’s vernal pools.

“Anything else you’re interested in is not going to happen if you can’t breathe the air and drink the water. Don’t sit this one out. Do something. You are by accident of fate alive at an absolutely critical moment in the history of our planet.”  ~ Carl Sagan 

“Our” vernal pools

For my first year, I wanted to start out rather small and close to home on wetlands that I suspected may fit the criteria for being vernal pools.   These are within Sterling Heights’ Clinton River Park property and really have no protections other than they are owned by the city.    I started out in the early Spring with the initial mapping and survey completion.   During the training, you are requested to draw out and measure the size of the pool that you are reporting on.   Easier said than done with rather large, dense areas.   Fortunately this year, the Vernal Pool Monitoring team began piloting use of the ArcGIS Collector app in their surveys and I was the first guinea pig.   The app allows you to use GPS tracking on your phone to walk the perimeter of the pool, which then calculates the area.  Quite handy for something so irregularly shaped.

The larger pool here ended up measuring 2.395 acres, which would have been quite difficult for me to measure manually.   The smaller sister pool is only 0.384 acres, but both are sizable pools to monitor.   I soon learned these were not so small to start with, just very close to home.

The rest of the survey involves measuring water temperatures, documenting the number of trees in the pools and on the perimeter, the type of substrate within the pools, and 2 pages worth of other data points.   The cool part was I found 2 indicator species present in both of them, wood frogs and fairy shrimp. I will never forget the one morning I visited the smaller pool to find numerous wood frogs all doing their mating calls.  

UPDATE for 2021: The Michigan Vernal Pools partnership created a new website and data hub here. It is a great resource full of training materials, an introduction to the new app Survey123 (replacing the ArcGIS data collector mentioned in this post) for data collection, and a map of all the vernal pools recorded in Michigan.