> > Oysters to go?

Of all the factors contributing to the collapse of coastal ecosystems, overfishing appears to be the worst-and not only the industrial fishing of the 20th century. Humans have been overfishing for centuries, says professor of geophysical sciences Susan Kidwell. The problem is, we have a taste for the sea's most important creatures: top predators like cod and water-filterers like oysters.

"The removal of so much of the higher portions of the food chain fundamentally transforms the residual ecosystem," says Kidwell, one of 18 marine ecologists, geologists, paleontologists, and archaeologists who published a study in the July 27 Science. Until now, ecologists have blamed culprits such as pollution, global warming, and invasive species for the collapse. But these only exacerbate problems caused by long-term damage to the food web. Agricultural-nutrient runoff, for example, is linked to the increased incidence of red tides-low-oxygen waters discolored by blooms of often deadly microorganisms.

"Sediment cores indicate [red tides] are naturally common in many estuaries," Kidwell says. "The ecosystem, because it has been degraded through overfishing, is unable to handle those nutrient inputs, whereas in the past it was able to."

In addition to enacting pollution controls, the researchers suggest restoring key organisms to shades of their former glory to let the food web do some of the work in restoring balance.- S.A.S.

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