A Great Lakes mystery: The case of the disappeari...( WEST LAFAYETTE Ind. - Throughout the...)

WEST LAFAYETTE, Ind. - Throughout the overlooked depths of Lake Michigan and other Great Lakes, a small but important animal is rapidly disappearing.

Until recently, the animal - a shrimplike, energy-dense creature called Diporeia - was a major food source for commercially important species like lake whitefish and many prey fish upon which salmon, trout and walleye rely.

Scientists are employing new research methods in a quest to explain their population freefall, which threatens to negatively affect the Lakes' ecosystems and $4 billion sport fishing industry, said Purdue University researcher Marisol Seplveda.

"We want to narrow down likely causes for this decline," said Seplveda, an assistant professor of forestry and natural resources. "It may help us halt the animal's further disappearance."

Seplveda has begun to identify substances involved in Diporeia metabolism, the set of chemical reactions that maintain life and allow organisms to respond to stress. Differences in levels of these metabolites between individuals and populations in various regions of the lakes may point toward the stressor or stressors responsible for their decline, she said.

In the same biological class as krill and shrimp, these rice grain-sized crustaceans dwell on lake bottoms and feed on descending algal plankton. Their bodies contain 30 percent to 40 percent lipids like fats and oils, making them a vital energy and nutrient source for the entire food web.

They are already gone from many large areas of lakes Michigan, Huron, Erie and Ontario, said collaborating researcher Tom Nalepa. In Lake Michigan, there are almost no Diporeia found at depths shallower than 90 meters. Just 15 years ago, their density often exceeded 10,000 animals per square meter at such depths, said Nalepa, a research biologist with the Great Lakes Environmental Research Laboratory.

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