Peering Into The Pool

If you’ve been following wondermyway for a few years, you know that each spring I make a bee-line for vernal pools, those shallow, short-lived ponds that fill with snowmelt or spring rain for at least several weeks most years, have no major inlet or outlet, and most importantly, no fish. Without fish, reproductive success is more likely for some amphibians, crustaceans, and insects who depend upon these ephemeral water bodies for breeding.

There are four indicator species in Maine that define a vernal pool as significant. Since 2007, significant vernal pool habitat has been protected by law under Maine’s Natural Resources Protection Act (NRPA): “Significant Vernal Pool (SVP) habitat consists of a vernal pool depression and a portion of the critical terrestrial habitat within a 250-foot radius of the spring or fall high water mark of the depression. Any activity in, on, or over the SVP or the 250-foot critical terrestrial habitat zone must avoid unreasonable impacts to the significant vernal pool habitat and obtain approval from the Maine Department of Environmental Protection, either through Permit by Rule (a streamlined permitting process) or full individual NRPA permit.”

Those four indicator species that define such significance: Wood Frogs, Spotted Salamanders, Blue Spotted Salamanders, and Fairy Shrimp. The pool must contain 40 Wood Frog egg masses, or 20 Spotted Salamander Egg masses, or 10 Blue Spotted Salamander egg masses, or one Fairy Shrimp. I’ve yet to see a Blue Spotted Salamander or its eggs.

Some may see these ponds as oversized puddles, but let your eyes focus and suddenly you’ll realize that they are places teeming with life.

As you do, it might surprise you to spot lots of flying activity just above the pool’s surface. It’s actually Midges on the move, trying to get a date so that there will be even more Midges on the move. They look rather like mosquitoes, but don’t bite, so not to worry.

Male Midges have a longer, more slender body that the females, and they like to posture in attempts to interest one of the opposite gender. They’re actually fun to watch.

Of course, equally, ahem, fun to watch are the larval forms of Mosquitoes as they wriggle and wraggle through the water column, some even forming dense clusters.

If you do some container dipping at a vernal pool near you in order to take a closer look, I trust you won’t dump these onto the leaf litter rather than back into the water. As much as the females annoy us once they morph into that annoying flying insect that needs to suck mammal blood to gain proteins and nutrients for their eggs, they play an important part in the food web.

Especially for warblers such as this Yellow-rumped that was part of a flock that arrived in western Maine this week–just as it should have, being the end of April. It was spotted quite near one of the pools, so I suspect Mosquito Mash will soon be on the menu.

Back to those four indicator species for a significant vernal pool . . . it was this week that while looking close up at some Wood Frog eggs, I realized we had babies in the form of tadpoles.

I saw “we” because mom and dad Wood Frog do not hang around. Once they’ve canoodled and eggs have been fertilized and deposited, they exit the pool and return to their upland habitat, where they spend the next fifty weeks, so it’s up to us to watch over their young ones. Their metamorphosis, or change to adult form, will be completed by late June or earlier should temperatures rise and the pool begin to dry out.

I encourage you , dear readers, to do what I do and stare intently into the leaf litter to see if you can spot some tadpoles. And who knows what else you might discover.

While looking into another section of the pool, you might notice another type of egg mass, this one coated with a gelatinous mass that encompasses all of the eggs. Spotted Salamanders made their Big Night return to the pools about a week or so later than the Wood Frogs, so the embryos are still developing.

I find it fascinating to see the little forms take shape. It’s like looking into a mother’s womb without medical devices.

Okay, it’s time for you to peer into the pool again. This time you are looking for Fairy Shrimp, those tiny crustaceans that are about a half inch long, swim on their backs, and move eleven pairs of legs like a crew team in a rowing shell. Remember, I said one Fairy Shrimp makes a pool significant according to the State of Maine. How many do you see in this photo?

Those in the first Fairy Shrimp photo are males, but females are present as well. The way to identify a female is to look for her two brood sacs that are positioned just under her legs or appendages.

So here’s the thing. Fairy Shrimp have a short life span, but . . . their eggs must dry out and freeze before they can respond to environmental cues such as reflooding to hatch. One of the pools I’ve been frequenting lately I’d only discovered last year and it had no Fairy Shrimp. The other day when I approached with some volunteer docents from Greater Lovell Land Trust, one exclaimed within seconds of our arrival, “Fairy Shrimp.”

That got me thinking: how is it that we didn’t spot any last year, and this year we started seeing them everywhere. Also, in another pool where we’ve often spied a few, we’ve noticed they are in abundance. Previous to this week, I knew that the eggs, known as cysts, can remain dormant for years, but assumed that if the pool flooded each year, they all hatched. It didn’t make sense though that one pool suddenly has shrimp and the other has so many more than normal. It was time to do a little research, and what I learned from the Vermont Center for Ecostudies , is that only a small portion of cysts hatch each year, thus leaving plenty more for the future. And temperature plays a key role in hatching. So I thought about winter 2021 and how we didn’t have a lot of snow and the temperature was on the mild side. This past winter was much snowier (though not enough still in my book) and much chillier. My unscientific conclusion, based only on limited knowledge and observation, is that conditions weren’t conducive in 2021 at that one pool and so no shrimp hatched. I’m already looking forward to next year.

For your enjoyment I’ve included a video of a Fairy Shrimp moving through a pool this past week. Fairy Shrimp indicate unpolluted water, so finding one is significant. Finding so many . . . bliss.

When you are peering into the water for such a long time, other life forms make themselves known, such as Predacious Diving Beetle larvae, aka Water Tiger. Just like the adult this insect will morph into, it eats everything including tadpoles and insects, and even its siblings sometimes.

It wasn’t just the docents and I who had fun at the pools, but also a group of middle school students I have the immense honor to work with each Friday and yesterday they enjoyed documenting life at the pool that suddenly had Fairy Shrimp this year. Quiz yourself on ID of the species one student scooped up in this bug box. And rest assured that these critters were released back into the pool after being studied for a few minutes.

As I said, I’ve done a lot of scanning this week, including on a couple of solo trips, and it was on one of these that I made one of my favorite discoveries: a Caddisfly larvae. In larval form, Caddisflies are resourceful architects who repurpose their surroundings to create their homes. Sometimes I find them constructed of hemlock needles topped with a maple flowers, and a friend sent a photo today of one she found who had built its house of grains of sand. My find . . . in the pool that suddenly had Fairy Shrimp this year: a mobile home built of leaves. It was so well camouflaged that only the movement made me realize what was before my eyes.

Larval Caddisflies eat various types of detritus, including bits of leaves, algae, and miscellaneous organic matter so they, too, are important as they break down what is in the pool.

If it wasn’t that I need to eventually find my way home and make dinner, I’d probably still be out there. But yikes, it’s 7:00pm, and I haven’t even started dinner, and my guy will be home from work soon, so I’d better get going.

If you are looking for me in the next few weeks, however, I’ll be the one with hands on bent knees as I hunch over the pool. Join me and we can peer in together.