The Lake Where You Live

We know about the annual migration of loons, of ducks and other waterfowl, of monarch butterflies, even the movements of fish within out lakes at different times of year.

But there’s another migration that occurs in our lakes that you probably didn’t know about. I didn’t either until I attended a meeting of lake advocates in Watersmeet, Michigan, on August 2. There Erick Elgin, a limnologist and water resources educator with Michigan State University Extension, described the migration of Daphnia from deep water to the surface every 24 hours.

Daphnia, commonly called water fleas, are tiny crustaceans that float about in the water as part of lakes’ zooplankton community. They are an essential food source for young fish, and that at least partly explains why their migratory behavior evolved.

Daphnia are called water fleas because their herky-jerky up-and-down motion in the water is reminiscent of the leaping ability of the fleas that can infest dogs. They propel themselves with a pair of appendages that function a little bit like oars.

These little creatures, no more than an eighth-inch in diameter and usually smaller than that, spend the daylight hours near the bottom of the lake, as far down as 50 feet. At night they propel themselves to the surface where they feed on the tiny algae that spent the day making food from the sun (photosynthesis) and multiplying. 

Fifty vertical feet is a long way for a tiny organism to travel, and yet they persist. So, why do they do it? Elgin explained that fish feed by sight, and if the Daphnia were near the surface during the day, fish would spot and eat them. But down in the depths where it’s dark even in the daylight hours, the fish can’t find them so easily.

That doesn’t mean none of the Daphnia get eaten. For one thing, Elgin reported, the light of a full moon, when the critters are at the surface, is enough to illuminate them so that fish can have a feast. Despite their daily evasive action, Daphnia are important to lake food webs.

Elgin also explained how Daphnia reproduce in two ways: through females cloning themselves and pushing out identical, fully formed offspring, and by mating with males to produce eggs that sink to the lake bottom to hatch later.

These are interesting creatures. They are small but not microscopic. If you were to collect a jar of water from your lake, you could well see Daphnia in it as white specks. If those specks were hopping about erratically, you could be pretty sure you have captured water fleas.

The meeting where Elgin and others spoke was a first, sponsored mainly by the Invasive Species Control Coalition of Watersmeet, a diverse partnership organized to help prevent and control invasive species’ spread among inland lakes in its area of Upper Michigan. Among about 75 attendees were a number of people from lakes in Wisconsin and border waters.

I hope the coalition does this again next year. It was a great place to meet other lake advocates and share concerns and success stories. 

Ted Rulseh is a writer, author and lake advocate who lives on Birch Lake in Oneida County. His new book, “Ripple Effects,” has been released by UW Press. You can learn about it by visiting his website at https://thelakeguy.net.