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Research Team Measures Physical, Chemical and Biological Activity in Lake Michigan
The waters of Lake Michigan just off the Wisconsin coast near Milwaukee are a busy place. There are boats that are part of industry. There are boats for fun, such as sailboats and motor boats. People swim. People fish.
There are also important activities happening in the water at a microscopic level. We can't see that activity. We usually don't think about.
Oceanographers Russell Cuhel, J. Val Klump and Carmen Aguilar, however, are very interested in what goes on in the water. This particular stretch of the lake is important to them because of the kinds of physical, biological and chemical activity that happens there. It is due to runoff, pollution and treated sewage coming into the lake from nearby Milwaukee. These things, called inputs have an effect on the lake. They also interact with things like light and temperature.
The three researchers work the University of Wisconsin-Milwaukee School of Freshwater Sciences. They regularly take water samples from locations in the Milwaukee Harbor. They also go out into the open waters of Lake Michigan near Milwaukee.
From their samples, they discover clues about the lake. These clues can be things like how fast algae and bacteria grow. Other clues are chemicals in the water, such as dissolved oxygen and carbon dioxide.
These clues help build a picture of how ecosystem changes affect the lake and the shores around it. These changes can be naturally occurring or caused by people. That's important because the physical, chemical and biological activity in the waters of this area of Lake Michigan can actually help eliminate some pollutants. This area of the lake also is important to grow baby fish such as yellow perch.
Mapping the Nearshore Food Web
Every environment has what’s known as a food web. It’s like a map that shows which animals eat (and are eaten by) other animals. Food webs can be very delicate. For example, on a beautiful summer evening, you might wish that all the mosquitoes in the world would stop biting your arms and just go away. In one way, it’s a nice thought. But it also might mean that the spiders in your backyard, who trap and eat those mosquitoes in their webs, might starve to death.
Taking away a piece of a food web can have an impact on all the web’s other parts. Adding a new and unexpected piece to the web also can have an impact to the whole web. That’s what’s happening in the waters near the shore of Lake Michigan. In the last few years, a new type of fish called the round goby has moved into this area.
Round goby breed quickly and eat a lot. That’s two reasons that scientists are worried. Gobies could be having an effect on the other fish that swim and feed in the lake. Harvey Bootsma and John Janssen have spent the last few years studying the food web near Lake Michigan’s shoreline. They are professors at the University of Wisconsin-Milwaukee’s School of Freshwater Sciences. Their work is funded by University of Wisconsin Sea Grant. Not surprisingly, they’re spending a lot of time focusing on the round goby.
“When we dive to do our research, there will be at least a hundred swimming around us, watching us work,” said Bootsma. “Numerically, they’re clearly dominant in the nearshore zone.”
Since May 2010, Bootsma and Janssen have been visiting two specific sites in the Wisconsin nearshore waters of Lake Michigan. One is sandy and the other rocky. They’re taking water samples from three different depths at each site. Each reveals something different about the nearshore food web.
Bootsma and Janssen are also working with research teams in Indiana and Illinois. They want to know if the gobies are having an impact in those states, too.
Other scientists have done research that suggests gobies really like to eat quagga mussels. Quagga mussels are a small, striped clam that has also moved into Lake Michigan. Bootsma and Janssen’s research is showing that when gobies grow to 10 centimeters and up they eat quagga mussels. By analyzing chemicals in the gobies’ body tissues they’ve discovered something interesting.
“The mussels are actually a side dish,” Bootsma said. “Most gobies, and especially the younger ones, are actually subsisting on other types of food.”
What are the gobies munching on? Tiny organisms that live in the green Cladophora algae that you’ll often see on the surface of the shallower waters of Lake Michigan.
Some scientists have thought the algae were a food-web “dead end. In other words, they thought it wasn’t a source of food for animals or fish. Now Bootsma and Janssen are worried the large numbers of gobies may be eating all the organisms in the algae. That takes food away from fish like yellow perch and spot-tail shiner.
Bootsma and Janssen are also trying to discover if other Lake Michigan fish like trout and salmon eat gobies. After looking at hundreds of samples for months, Bootsma and Janssen plan to study even more sites on Lake Michigan. Is what they found so far happening in other nearshore places? “We’re interested in learning if the patterns around Milwaukee County are typical of the whole lake,” explained Bootsma.
If they are, Bootsma and Janssen’s work could help to determine how many different types of fish Lake Michigan’s food web can support. That would also help determine what other fish could be added. That is called stocking fish. It would balance out the food web. Stay tuned.