HOUMA, La.—Oysters are dying in their beds in the brackish marshes of southern Louisiana, but the culprit isn’t oil spilling from the Gulf. It is, at least in part, fresh water.
In April, soon after the oil spill started, Louisiana officials started opening gates along the levees of the Mississippi River, letting massive amounts of river water pour through man-made channels and into coastal marshes. It was a gambit—similar to opening a fire hose—to keep the encroaching oil at bay.
By most accounts, the strategy succeeded in minimizing the amount of oil that entered the fertile and lucrative estuaries. But oyster farmers and scientists say it appears to have had one major side effect: the deaths of large numbers of oysters, water-filterers whose simplicity and sensitivity makes them early indicators of environmental influences that ultimately could hit other marsh dwellers too.
State officials say it’s unclear to what extent the fresh water releases are responsible for killing oysters.
The oyster deaths in Louisiana—which produces more than a third of U.S. oysters, more than any other state—are just the latest reminder that efforts to protect this delicate ecosystem from the oil spill could produce environmental damage of their own. Louisiana and federal officials have quarreled over an ongoing state project to build large sand berms to fend off incoming oil, with some federal officials fearful that they could actually intensify erosion. And chemicals, known as dispersants, sprayed on the oil in the Gulf to break up oil slicks might contribute to underwater oil plumes that could harm marine life, some scientists say.
Some marshes have been so inundated with fresh water that their salinity has plummeted to levels oysters can’t easily survive, some scientists say. Deprived, at least temporarily, of the salty water they need, large numbers of the two-shelled crop that has defined this region’s economy and culture for generations are dying off—even in parts of the Louisiana coast that appear to have been untouched by the spilled oil itself.
Full-strength seawater typically contains roughly 35 parts salt per thousand parts water, scientists say. Some of the southern Louisiana waters most productive for oysters contain 15 or more parts salt per thousand parts water, said Earl Melancon, a biologist at Nicholls State University in Thibodaux, La.
But in recent weeks, Mr. Melancon said, some waters in the vicinity of southern Louisiana’s Barataria Bay have been found to have salinity levels below five parts salt per thousand parts water. Even the hardiest oysters, he said, have trouble surviving in that.
“They’re dead, and they’re dead because of fresh water,” said Nick Collins, 38, an oysterman in Golden Meadow, La., citing government measurements of reduced salinity levels in the area.
Over the century that Mr. Collins’s family has been growing and harvesting oysters in Snail Bay, near Barataria Bay, innumerable hurricanes have sunk some of his family’s boats and ripped apart their houses, he said. But no natural storm ever decimated the Collins Oyster Co.’s about 2,000 acres of oyster beds as much as the river water unleashed in recent weeks by state officials appears to have done. Mr. Collins surveyed some of his family’s oyster grounds on Friday and found cluster after cluster of empty shells flapping apart—meaning the animal inside was dead.
Wholesale oyster prices at P&J Oyster Co. have risen about 20% since the oil spill started and they are likely to rise further, said Al Sunseri, president of the longtime New Orleans oyster processor and distributor. “It’s Economics 101,” he said, citing the laws of supply and demand.
Patrick Banks, the biologist at the Louisiana Department of Wildlife and Fisheries who oversees the state’s oyster fishery, said his office recently tested the waters in one of the most productive parts of Barataria Bay and found that roughly 60% of the oysters had died. In other areas of the bay, he said, the mortality level was around 10%.One die-off a few weeks ago was so extensive that visible masses of oyster meat were floating on the bay’s surface. “It looked like a fish kill,” said Mr. Banks, explaining the kill occurred “so fast and was so large that the predators that normally would eat up the oyster meat just couldn’t keep up.”
He blamed the deaths on the combination of summer heat and the salinity drop triggered by the opening of the fresh-water channels, known as “diversions”—a decision made by officials in another state office who were attempting environmental triage. “The state took the measure to try to protect the interior marshes,” Mr. Banks said. “These are just some of the effects of that.”
A spokesman for the Louisiana Coastal Protection and Restoration Authority, the state entity that oversaw both the berm construction and the river-water release, said it is “obvious” that the state’s fresh-water releases reduced salinity in the oyster beds.
But he said those intentional releases were just one of several factors contributing to the salinity drop; others included rain and the natural flow of the river. Linking a specific number of oyster deaths to the fresh-water releases will be difficult, he said.
The authority’s chairman, Garret Graves, said in a written statement that state officials “are currently evaluating all of the adverse effects associated with the oil spill and that BP PLC “is expected to pay” for all spill-related damage.
A BP spokeswoman said the company is “committed to paying all legitimate claims” but declined to say whether the oyster deaths are among them.
In an underlying irony, the channels that ferried the river water into the marshes, apparently killing oysters, were built over the years largely at the oyster industry’s behest.
Decades ago, the construction of levees along the Mississippi River effectively stopped the river from flooding adjacent land. But that meant the river’s fresh water no longer inundated the marshes each spring, annual rite of ecological renewal. That sent the salinity in many marshes too high, threatening oysters.
After years of wrangling between the state and the oyster industry, officials built the channels as a way to restore some of the fresh water into the marshes.
This spring, when the oil spill happened, state officials saw the channels as a tool to help keep out the oil.
Mr. Melancon, the Nicholls State biologist, is attempting to measure the extent of oyster deaths from the fresh-water diversions. “Have these diversions created more harm than good?” he asked. “I am not going to be the person to make that determination. But it certainly has harmed the oyster industry more than the oil.”