Dead clams tell many tales( Inventories of living and dead organ...)

Inventories of living and dead organisms could serve as a relatively fast, simple and inexpensive preliminary means of assessing human impact on ecosystems. The University of Chicago's Susan Kidwell explains how measuring the degree of live-dead mismatch could be used as an ecological tool in the Oct. 26 early online edition of the Proceedings of the National Academy of Sciences.

"We affect ecosystems in many different ways, but the effects of our actions are hard to pin down because we rarely have scientific data from before the onset of those impacts," said Kidwell, the William Rainey Harper Professor in Geophysical Sciences at Chicago.

Detailed ecological data, when they exist at all, often go back no more than 50 years. But scientists would prefer a deeper historical perspective that covers centuries or even a millennium. Live-dead studies can provide some of the needed perspective, according to Kidwell. In these studies, scientists collect data on the living organisms and the skeletal remains found in a specific ecosystem, then evaluate how closely they match.

"Death assemblages are what we call time-averaged. They're like time exposures," Kidwell said, "because skeletal remains can hang around for a long time. In fact, through radiocarbon and other dating methods we know that shells can persist within the upper few inches of the sea floor for decades and even millennia in some circumstances."

Scientists have conducted many such studies over the last several decades. Their initial motivation had nothing to do with documenting the ecological impact of humans. The goal instead was to determine to what extent natural processes altered the record that living organisms had left behind for potential fossilization.

Kidwell's research focuses on coastal and open-marine settings, where disruptions range from dredging and bottom-fishing to the chemical byproducts of urbanization and agriculture that flow
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