Article posted Wednesday, March 25, 2015 2:30pm

In addition to the loss of Diporeia, a major food source for fish in Lake Michigan, there are other challenges to the Great Lakes ecosystem, including the arrival of zebra mussels about 1980 and quagga mussels in the 1990s. These invasive species hitchhiked from overseas in ballast of ocean-crossing cargo ships. As filter feeders, the mussels began to remove single-celled algae, the favored food of Diporeia. The diminished population of algae increased the clarity of Lake Michigan and encouraged growth of extensive strands of filamentous algae such as Cladophora . Phosphorus run-off from land and the enhanced excretion of phosphorus by quagga mussels also stimulated this growth. To further complicate lake ecology, the Round Goby, native to the Black Sea of Russia, showed up in the Great Lakes. These rather ugly, big-eyed fish measure 4 to 10 inches long and eat both fish eggs and the few Diporeia left in Lake Michigan. Its scientific name, Neogobius melanostomus, means “new little fish” with “black mouth.” Bass fishermen in Green Bay often hook more gobies than bass. What does the future hold for Lake Michigan ecology? Diporeia, a favorite food of whitefish and other fish, is disappearing. Zebra mussels that helped clear the lake of Diporeia food are now showing up in the stomachs of area fish. Meanwhile, gobies also eat zebra mussels and growth of Cladophora clogs our shorelines. What is happening in Lake Michigan is basically a competition between native and invasive aquatic species in order to reach some kind of ecological equilibrium. This is a classic biological back and forth that will take years to resolve, but it is important to keep in mind that food supply will ultimately determine which species is the fittest. (Science Daily, April 11, 2013; Aquatic Invasions, Jan. 11, 2011, p. 175-194; The New York Times, May 26, 2011; Science Daily, April 17, 2011; Purdue Univ. News, May 28, 2008)