Fairies in the Forest

What is swimming in that vernal pool

By Julie Reiff

Vernal pools, the depressions in the land that collect rain and snowmelt this time of year, are a kind of mud-season miracle. They only last a few months, but in that time they provide food, shelter, breeding ground, and of course water, to a variety of creatures. They even help purify and recharge ground water.

What I find most remarkable are the fairy shrimp that depend on these temporary pools. We have two species in New England: Vernal Fairy Shrimp (Eubranchipus vernalis) and the Knob-lipped Fairy Shrimp (E. bundyi), which is more common up here in the north. They eat the algae and plankton, helping preserve water quality, and prefer the larger pools that form in undisturbed woods this time of year.

Knobbedlip Fairy Shrimp (Eubranchipus bundyi ). Photo by Steven Wang on iNaturalist — Knobbed-lip Fairy Shrimp *(Eubranchipus bundyi)* swim on their backs. Photo by Steven Wang on iNaturalist

To hatch, fairy shrimp need the right conditions of temperature, light, and oxygen. Vernal pools are not reliable places either. Some years they dry out before shrimp have time to mature. In others, excess rain or flooding might keep the pool from drying out, which the shrimp require to complete their life cycle.

In an amazing adaptation, only a portion of the fertilized eggs will hatch in a given season. In extreme conditions, that might be as little as 3 percent. The eggs themselves might persist in the leaf litter at the bottom of a pool for decades or possibly centuries. Remember sea monkeys? These are their fresh water cousins.

To hatch, fairy shrimp need the right conditions of temperature, light, and oxygen. Vernal pools are not reliable places either. Some years they dry out before shrimp have time to mature.

Salamanders and dragonfly larvae feed on the shrimp. So do ducks and other waterfowl, but in doing so, they stomp around and collect the sturdy eggs on their legs and feathers, carrying them to other pools and helping the species to thrive.

In the next few weeks, keep an eye out if you walk in the woods. If you’re lucky you might come across a vernal pool, and if you’re even luckier, you might get to witness a mud-season miracle.

There is a Vernal Pool walk at 1 pm on Sunday, April 27 (after the pancake breakfast at Gemini). I can’t guarantee we’ll see fairy shrimp, but I can promise we’ll find interesting creatures. I’m keeping an eye on several pools, and we’ll visit the one that looks most promising that day. Closer to the date, we’ll share the specific location with those who’ve registered.