( Fish kills foul odors and closed beach...)'Dead zone' summer killed billions of ocean state mussels

Fish kills, foul odors and closed beaches hit Rhode Island's Narragansett Bay during the summer of 2001. The culprit was hypoxia, or oxygen depletion, which literally suffocates sea life. While some evidence of this "dead zone" could be seen on the bay's surface, Brown University ecologists went underwater and discovered a massive mussel die-off.

In a survey of nine mussel reefs located in the central bay, researchers found one reef completely wiped out. Of the remaining eight, seven were severely depleted. The ecologists estimate that the number of mussels that died was roughly 4.5 billion, or about 80 percent of the reefs' population.

Just one month before hypoxia hit, researchers surveyed the same reefs and saw acres of healthy, densely packed mussels blanketing the estuary floor.

"What we saw was a local extinction," said Andrew Altieri, a new Ph.D. graduate from Brown University's Department of Ecology and Evolutionary Biology. "The mussel population was devastated. If the magnitude of this die-off was visible from the surface, there would've been public alarm."

Altieri conducted the surveys with Jon Witman, a marine ecologist and an associate professor in the Department of Ecology and Evolutionary Biology. In a report on their research, published in Ecology, Altieri and Witman show that mussel die-off had a lasting effect.

In fall 2002, one year after the die-off, the pair found that only one of the nine reefs was recovering. Altieri and Witman wondered how the loss of so many mussels, which filter minute algae called phytoplankton from the water, might affect the bay's ecosystem.

So Altieri calculated the filtering capacity of mussels in the reefs, before and after the hypoxic event. They found that the healthy mussels could filter the equivalent of the entire volume of Narragansett Bay in just 20 days. But within weeks of the die-off, that filtering capacity dropped by 75 percent.

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Source:Brown University

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