A Great Lakes mystery: The case of the disappeari...(r feeders with an overlapping diet - lar...)

"We don't know why Diporeia are responding so negatively to the mussels," he said.

Seplveda is looking into another possible contributor to Diporeia's decline: water pollutants like pesticides, polychlorinated biphenyls (PCBs), flame retardants or others.

Detailed in a study to be published in print and online next month in the journal Aquatic Toxicology, Seplveda measured Diporeia's response to a common pollutant and also began to identify differences between declining populations in Lake Michigan and those native to Lake Superior, the only Great Lake where populations remain stable. The latter comparison found the groups shared only 5 percent of their total metabolites, suggesting that animals from the two lakes are biologically quite different, Seplveda said.

"The answer to Diporeia decline may be found in these variations," she said.

Seplveda and University of Michigan researcher Tomas Hook were awarded a four-year, $560,000 grant by the Great Lakes Fishery Trust in January of this year to further investigate possible causes for Diporeia's decline. Both researchers are co-principal investigators of the project.

"We are casting a wide net to basically address a number of hypotheses at the same time," said Hook, a fisheries ecologist hired by Purdue who will begin work there this July.

In Seplveda's study, she and her team contrasted levels of metabolites between a group of control animals and that of an atrazine-exposed population of laboratory-reared Diporeia. They found that animals subjected to atrazine, a commonly used pesticide present in minute levels in Lake Michigan, significantly increased or decreased bodily production of five identifiable chemicals. These included an insect pheromone, a fatty ac
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