Great Lakes Fish Food Disappearing

C H I C A G O, Feb. 5 -- A primary source of food for young fish isquickly disappearing from the Great Lakes, according to scientistswho fear it could jeopardize decades of progress in restoring fishpopulations.

Diporeia, half-inch-long shrimp-like crustaceans, already areextinct in Lake Erie and declining at alarming rates from lakesMichigan, Ontario and Huron — a phenomenon scientists suspect islinked to zebra mussels, a Black Sea native that arrived in thiscountry in the late 1980s.

"It's one of those issues that is just so scary because … wehave seen such recovery [of fish species] in the 30 years since theClean Water Act was passed," said John Gannon, science coordinatorat the U.S. Geological Survey's Great Lakes Science Center in AnnArbor, Mich. "We had this wonderful success story running and thenone of the main food sources starts to disappear."

Base of the Food Chain

The demise of diporeia could have dire consequences for manytypes of fish, scientists said. Many fish that eat diporeia in turnare eaten by larger fish such as salmon and lake trout. The problemhas not affected such sport fish, but whitefish, which arecommercially harvested, have suffered.

Exactly what is causing diporeia, which live on lake bottoms, todisappear remains a mystery.

One theory is that zebra mussels, thumbnail-sized mollusks thatarrived in the ballast water of oceangoing ships, are competingwith diporeia for the same food — and winning, said Marc Tuchman,an environmental scientist in the EPA's Great Lakes NationalProgram Office in Chicago. Both dine on bacteria and algae, but themussels multiply rapidly and can filter vast amounts of water.

There also is speculation that there is enough food but musselsare extracting from it a nutrient essential to diporeia, thatmussels introduced a pathogen lethal to diporeia, or that amucous-like substance excreted by mussels is killing diporeia, saidThomas Nalepa, a research biologist at the Great LakesEnvironmental Research Lab in Ann Arbor. The lab is part of theNational Oceanographic and Atmospheric Administration.