CHICAGO — Lake Michigan is home of 300-pound sturgeon, but it's also the habitat of numerous animals that are as small as your fingernail and look like aliens.
In fact, the sturgeon — the lake's largest inhabitant — couldn't survive without the tiniest organisms.
"Even the biggest fishes, whether it is a sturgeon or perch or trout, feeds directly or indirectly on the smallest organisms," said Phil Willink, senior research biologist at the Shedd Aquarium. "All are interconnected through the Lake Michigan food web. Without the smaller organisms, there would be no larger ones, the tiniest creatures form the foundation of the food web. And they look really cool under the microscope."
Here are a handful of Lake Michigan's smallest organisms, with descriptions from Willink. And, as Willink said: "When we see drops in numbers of these tiniest creatures, there is often a decline in fishes soon afterward."
"A single invasive zebra/quagga mussel is the size of a fingernail. A solitary individual has a negligible impact on the ecosystem. But zebra/quagga mussels are present in such enormous numbers that they are effectively pulling biomass out of the water column and concentrating it along the bottom of Lake Michigan. These small organisms are fundamentally changing how some near-shore ecosystems are functioning, forcing scientists to rethink how certain processes drive the biological aspects of Lake Michigan."
"Most people are familiar with these as pill bugs or sow bugs in their gardens or backyards. The ones in Lake Michigan are the same size, but different species. They are not particularly good swimmers, tending to crawl around in small spaces along the bottom of the lake, eating decaying plants and other critters even smaller than themselves. Fishes love to crunch them down."
"There are native and invasive amphipods in Lake Michigan, and there is the usual concern that the invasives are replacing the natives. That said, as far as I can tell, fishes are equally happy to eat either of them. More interestingly, amphipods live in tiny places, scooting from cover to cover. They eat decaying matter and other critters even smaller than themselves. This habitat perfectly describes the spaces between shells in a quagga mussel colony. Unexpectedly, we may actually have more amphipods today along the Chicago lakefront than we did prior to the quagga mussel invasion. Since some fishes love to eat amphipods, there may actually be more food for fishes that live along the bottom than there used to be. A similar argument can be made for isopods, but amphipods are much more abundant than isopods."
"Water mites are extremely tiny, smaller than a pinhead. Most people have no idea they even exist. Although they are fairly common, they are not usually abundant, so they probably do not play a huge role in the food web. Even though they are not ecological heavyweights, they are great fun to watch under a microscope. This is because they are distant cousins to terrestrial mites and ticks, and even more distant cousins to spiders and such. So they are like extremely miniature spiders crawling around on the bottom of Lake Michigan looking for even tinier prey. (Please note that a picky scientist would tell you that they are definitely not spiders! Just really distant relatives.) And apparently they are quite voracious … for their size."