For Love of Lakes

Lady Daphnia’s World

· · 72 · · Lady Daphnia’s World Atsomepointyouareseeingsointenselythatyoubecome whatyousee,youmergeintothedropofwateruntilthe“you” disappears.Thehowandwhysandwhereforesdisappeartoo.Yet whenyouemergeyouaresomehowreplenished. PADNA HEJMADI I sidle up to the edge of cattails, settle myself on the bottom of the canoe, and leanoverthesidetogetmyfaceasclosetothewaterasIcan.Iampushingthe season by coming in early May. Populations of the creatures I seek normally peak in June, when the water has warmed. Aquarium aficionados and students know my quarry as waterfleas or daphnia. Lake biologists know them as cladocera (cla-da’-ser-a), tiny kin of lobsters and crayfish. I know them as fascinating creatures in lakes that first endeared themselves to me in college days. I also know them as members of the plankton, that vast assemblage of algae, tiny animals, and bacteria freely suspended in lakes. In our world of mega and supersized, things as small as plankton don’t project much significance. Can objects so small really matter? Don’t doubt it for a moment. A lake without plankton would be like an orchestra without violins. A lake without plankton would be a lake without fish. Yet barriers to knowing the plankton are formidable. Nothing in our experience in a terrestrial world compares to plankton. Most plankters are very small, visible as specks of green or bits of movement. Worse, they are submerged, making them difficult to see regardless of size. · · 73 · · Daphniaaremastersatfilteringalgaefromalake. Waterfleas are among the largest of planktonic animals, and the largest waterfleas likely to be seen are a group known as daphnids. They can provide a window into the plankton world. This is my first search for daphnids in Diamond Lake. The lake is calm this morning and the water notably more clear than in my mind-bending visit in August eight months ago. My Secchi disc reveals water clarity at midlake at two and a half feet, over six times as clear as it was then. The greenish cast to the lake today reveals plankton, plankton everywhere , the vast majority are blue-green algae. Cladocerans would be difficult to find among the dense blue-greens. I will look for them instead in my favorite nook of the lake, a southwest bay that receives pleasantly clear water from a small inflowing creek. Lakes snuggle up to the land most intimately in small bays protected from prevailing winds. This is such a bay. Sheltered by the bay’s shape and strategically positioned cattail stands, inhabitants of its waters escape the pounding chaos delivered by waves and wind from nearly all directions. Daphnians should thrive in such quiet waters. Animated bits of life flit between plant stems. I scoop water quickly lady daphnia’s world lakescapes· · 74 · · with a bottle and peer in. Cladocera can be as large as small ants, and I recognize them in my jar by the jerky flealike way they propel themselves through the water. Counting them is difficult. All are in motion. I judge there to be ten. Most are young. A single large daphnian with pastel salmon tint ascends in slow hops. No matter how often I dip these bits of life from lakes and ponds, the fascination is lessened not one whit from the first. I am no different than my students when they first see these creatures with a bit of magnification. I can only guess at what incites our passions. Feathery legs flail inside an open chamber. Antennae stroke vigorously downward, propelling the creatures through the water in their characteristic hopping style. Explosive extensions of springlike legs kick others along the jar’s bottom. They appear much more complex inside than seems possible in an animal the size of a kernel of grain. Cladocera are disc-shaped with bundles of organs stuffed inside rigid taco shell-like coverings. The transparent shell displays a beating heart, a pulsing intestine, and babies repositioning themselves in a crowded brood chamber. A large single black eye in continual motion dominates the head. Who would expect these organs of ours inside such a grain of life? Maybe it’s the astonishing complexity in such a tiny package that captivates my students and me. “Oh, Dr. Nelson, come look at this! Is this the heart? It’s beating!” Zoologists may view the heart as merely an animated pump, but the irresistible pulsing mesmerizes my students. The rhythmic beat touches a deep chord in some psychological language, that our words—heartwarming, heartfelt, heart of the matter—reinforce. What must life be like for so small a creature submerged in...