R.I. Shellfish Offer Clue to Health of Chesapeake

Newell calculated that at their current numbers, the bay's oysters would need a year to filter its entire volume.

But without enough shellfish around, Newell must rely on computer models to estimate the impact. "This is all educated arm-waving, because you can't go back in time," he said.

That historical view is what Altieri and Witman gained in Rhode Island. Ironically, the pair were investigating an unusual boom in blue mussels in 2001 that local watermen called "a once-in-20-years occurrence," Witman said. The nine reefs they studied covered the equivalent of 229 football fields. Lying open in rows, the creatures gleamed blue-black and red, attracting crabs, sea stars and fish that eat them and live in the reefs. Snorkeling over them, the ecologists could see the reefs through 20 feet of water in a bay where average visibility is about four feet.

Altieri calculated that the reefs were processing the bay's entire water volume once every 20 days, even though they covered less than 1 percent of the bay floor.

Then one day in August, the men saw sea stars and crabs in the reefs climbing higher, searching for oxygen. Altieri noted that dissolved oxygen in the water had plummeted.

Within days, a hypoxic episode triggered by warm weather, low wind and the usual nutrients contributed to fish kills and beach closures around the bay. Two months later, mussels lay scattered like broken pottery on the bay floor, silted over and empty, more than 4 billion of them. Their filtering capacity had dropped by 75 percent.

One reef died entirely. A year later, seven of the other eight were mostly dead, too.

"The magnitude of mortality that hypoxia could cause . . . had never been documented" in the Narragansett, Witman said. "We had the ability to look at effects on individual species and the entire ecosystem." The damage from that one event, they estimated, could take more than a decade to undo.

The study has stocked the arsenals of the Chesapeake's oyster restoration advocates. Virginia and Maryland have spent tens of millions of dollars on oyster restoration and billions on bay cleanup over the past three decades, but they have not significantly curtailed oyster harvests. Meanwhile, the beleaguered industry has turned to a mechanized process called "power dredging" to maximize skimpy harvests, further threatening the oyster population. Some have proposed introducing a disease-resistant Asian species, but environmentalists argue that could have unintended consequences for the bay's battered ecosystem.

"It's very compelling," Maryland's Newell said of the Narragansett report. "The more examples like that we have, maybe we can get people" -- he paused for a short laugh -- "to actually change policies."