Fairy Shrimp

Last weekend while looking for amphibian egg masses in the wetlands, we found an abundance of water springtails. This past weekend we were looking for egg masses again and it still seems a little early because we didn’t find any. Not to worry because we saw a fascinating creature called a fairy shrimp.

These translucent crustaceans are related to lobsters and crabs. One of the first things I noticed is that they swim upside down! They have 11 pairs of legs waving back and forth toward the surface and I was hoping for others to join this one to perform a lovely, synchronized swimming display. Next time I will try playing some music to inspire them.

In addition to propulsion and dance routines, their legs somehow function as gills allowing them to absorb oxygen in the water and breathe! That’s not all. Their magical legs also help to filter food from the water or scrape food from surfaces.

They live in temporary habitats that only fill with water for part of the year called vernal pools. Since their aquatic habitat is a seasonal or ephemeral arrangement, they have a short life span.

So, they are among the first eggs to hatch out in early spring or late winter. This ensures they can complete their lifecycle and lay their eggs before the habitat dries up. The shrimp in the photo is a female and you can see the brood pouch which holds eggs, located directly behind the legs. The fairy shrimp eggs are called cysts. It’s okay if the pool dries up because the eggs can survive, sometimes years, until the rain returns. They can even survive freezing winter temperatures. In addition, I found a page on the U.S. Fish and Wildlife Services (USFWS) website that says the cysts can withstand being ingested by animals! Even more fascinating, the cysts can be “then deposited in new habitats when the animal urinates (USFWS).” Wow! The bottom line is that “fairy” signifies that these are magical creatures.

How else do fairy shrimp cysts get dispersed through the landscape? The USFWS writes, “Aquatic birds are the most likely agents of dispersal of vernal pool fairy shrimp. Large mammals are also known to act as distributors by wallowing in dirt, getting cysts caught in their fur and transporting the cysts to another wallow.”

Being adapted to surviving the temporal nature of vernal pools has another advantage. These pools are generally not connected to permanent streams or lakes that could allow in predatory fish. The water here in the wetlands does drop significantly because there is only an occasional rain shower during the summer months here in the Willamette Valley. There is always a little water at the Adkinson Bridge, which supports small fish, bullfrogs, turtles, and other animals that could potentially prey upon fairy shrimp. I think the water disappears, and the land dries out in the upper part of the wetlands where the fairy shrimp were found.

That said, fairy shrimp are a part of the food chain. We flushed out some wood ducks when wading back into the upper part of the wetlands, and I’m sure they found a few fairy shrimp to nibble on.

Oregon is home to 14 species of fairy shrimp. This one has blue tips on its tail. Check out the short video below to watch them swim. Nature is an inexhaustible source of wonder. I look forward to seeing you out there.

Resource
Vernal Pool Fairy Shrimp (Branchinecta Lynchi) | U.S. Fish & Wildlife Service. https://www.fws.gov/species/vernal-pool-fairy-shrimp-branchinecta-lynchi. Accessed 26 Jan. 2025.

Water Springtails

While looking for frog eggs with the habitat committee, I noticed all these tiny specs floating on the water. They were unidentifiable as you looked at them on the surface. You could only observe that they ever so slightly jumped around as you waded through them. They were sprinkled everywhere on the surface but also formed dense rafts as they congregated on blades of grass on top of the water. I put my macro lens on my phone camera to get a closer look at this mystery and hopefully figure out what they were. The first photo is the fixed 10x lens, and in the second photo, I zoomed to 2x on my phone. The photos revealed a wrinkled, gray creature with pink legs! Based on how they hopped in every direction, someone in the group wondered if they were a species of springtails. I submitted the photo to iNaturalist and it suggested that they were water springtails (Poduridae). Looking up photos, I found them to closely match Podura aquatica.

In my research, I found out that they eat decaying organic material, so it makes sense that they were hanging out of these blades of grass. So they are one of the many necessary decomposers that help break down vegetation to return nutrients to the environment and keep the water clean. I hope that their presence indicates a healthy, thriving wetlands ecosystem.

It was fascinating to see so many, and I wondered what prompted them to want to hatch out in great numbers now.

I also discovered that springtails are not insects. Biologists have classified them as part of the class Collembola, not Insecta. They are both hexapods (6 legs), but the key difference that prompted this distinction is springtails have internal mouthparts, unlike insects which have external mouthparts. I am still researching this, but I thought I would pass it along for your curiosity.

Pacific Treefrog Eggs

On Sunday, members of the habitat committee at the arboretum went looking for amphibian egg masses. We waded around in the wetlands for a couple of hours and weren’t able to find any out there yet. The water level is fairly high at the moment from all of the recent rain, so we weren’t able to survey all of the locations that we wanted. Also, there are heaps of fallen tree limbs clogging the area from last year’s ice storm. That said, we were able to find egg masses of the Pacific Treefrog in the shallow pools around the parking lot. It will be interesting to see how viable these eggs are this early in the year and when they might hatch during the cold, winter weather. As friendly reminder to help protect these creatures, please remember to keep your dogs and children out of the shallow pools found throughout the arboretum like around the parking lot and the area known as The Seeps along the road that goes above the wetlands. Thank you. As the evening approached, the males started vocalizing their beautiful choral croaks, music to my ears. Spring is on its way!