By PHILLIP WELDY / stewardship manager, Central Indiana Land Trust
When you’re walking in the woods in the spring, it’s clear that life is all around you. Giant trees tower above you. The birds sing with their melodious voices. At your feet, ephemeral flowers bloom in radiant hues of color. Surrounded by beauty, it’s easy to be captivated by the things readily available to our senses.
And if these things are all you notice during your time in the woods, it’s time well spent.
But nature has many secrets that aren’t apparent at first. It’s worth taking a closer look – even at that puddle along the trail.
One of the most unassuming habitats within our Indiana flatwoods are vernal pools. These are pools of water that fill in the spring and recede completely as the year goes on. They vary in size ranging from sizeable pond to small puddle.
But regardless of size, they can hold wonders. If you pause a bit, sometimes up to a minute for your eyes to adjust, you’ll start to see the life that dwells in these pools. They can be home to all sorts of species who need calm waters to complete a part of their life cycle. Many amphibians, insects, and other critters spend part of their lives in these seasonal pools.
When we think about creatures of the forest, crustaceans tend to be at the bottom of the list, if they even make the list. But there are several crustaceans that live in our woodlands. Many of them use vernal pools. One of these is fairy shrimp!
Fairy shrimp (Eubranchipus vernalis) are tiny freshwater crustations. At only 0.12 to 1.5 inches long, they live their entire life in these temporary pools of water. They’re classified in the order Anostraca, and their origins date back to fossils found from the Cambrian Period. That’s a lineage even older than fish.
You’ll know fairy shrimp by several characteristics, including their often bright-orange coloring. They can also be red, bronze, white, green, or blue. Their eyes are on raised stalks, and they swim “upside-down.”
But there’s a brief window to find them, because they are only active for a short period of time. They hatch as larvae in late winter or early spring, then spend up to two weeks in molting phases, then one to three weeks as a reproducing adult. Adult populations generally disappear by mid-May. That’s when water temperatures warm to the upper 60s and predation increases. Fairy shrimp make up just one part of a whole ecological web of life in a vernal pool—and their predators are dragonfly and salamander larvae.
The species’ entire existence is dependent on a disappearing pool of water, so it has adapted its life cycle to that fact. After the eggs are fertilized, they become fully developed embryos, known as cysts, which settle in the sediment at the bottom of the pool. They remain there throughout the year after the water has dried up. Because vernal pools are a fleeting habitat, embryo dormancy (rather than egg dormancy) is key to survival. With the cysts lying dormant, fairy shrimp can emerge immediately when conditions are right.
Of course, seasonal pools are always at risk of drying up before the shrimp can reproduce. But fairy shrimp have another evolutionary trick up their tiny sleeves. Only a portion of the total population of cysts hatch in a given year. That means a bank of unhatched shrimp can last several decades, ensuring survival.
Despite the seasonality of vernal pools, as long as the habitat lasts, fairy shrimp will likely survive. Which is another reason why wetlands are important and worth protecting. That goes even for the unassuming puddles in a forest.
So the next time you pass a pool of water on a hike (perhaps at a Central Indiana Land Trust nature preserve), be sure to take a moment to peer inside it. Whether or not you spy an elusive fairy shrimp, you might be surprised to see all the life that calls this fragile habitat home.
Headquartered in the Old Northside, Central Indiana Land Trust partners with conservation organizations statewide to preserve the best of Indiana’s natural areas, protecting plants and animals, so Hoosiers can experience the wonder of the state’s natural heritage. Find hiking destinations at conservingindiana.org.
