At the bottom of the lake shrimp-like creatures, microscopic plankton, tiny fish, crustaceans, and invertebrates, work together to form an intricate food chain that supports the Great Lakes fishery. The star of the biological drama is a tiny shrimp-like creature called Diporeia. But this began to change in the early 1990s, after transoceanic freighters imported zebra and quagga mussels from the Caspian Sea.
In no time the foreign mussels took over the stage, gave Diporeia its walking papers, and rewrote the biological script for these freshwater seas. The disappearance of Diporeia was terribly significant: The six-legged amphipods with an orange hue on their shrimp-like bodies accounted for up to 70 percent of the living biomass on the bottoms of healthy lakes.
A one-time population decline in an isolated pocket of one lake did not constitute a crisis. But sampling revealed signs of an alarming trend: Diporeia were vanishing from entire regions of Lake Michigan. It is said that population density of quagga mussels reaching 16,000 mussels per square meter. Tom Nalepa, a biologist for the National Oceanic and Atmospheric Administration, said that there is a tremendous shift in the living biomass taking place on the bottom of Lake Michigan.
It is told that the sudden decline of Diporeia began shortly after zebra mussels started colonizing the near-shore areas of Lake Michigan in 1990. The arrival of the quagga mussel two years later accelerated the demise of Diporeia. The virtual elimination of Diporeia sent shock waves up the Great Lakes food chain. Commercial fishing operations and sport anglers felt the repercussions across much of the Great Lakes.
