Effort to keep oil spill at bay tips ecological balance

There’s a destructive liquid flowing into the Gulf of Mexico — and it’s not oil.

It’s the muddy fresh water of the Mississippi River, which has been released from southern Louisiana’s vast levee system and into estuaries in greater quantities than usual. The goal has been to use the rush of fresh water to keep sticky oil from reaching the sandy shores of the state.

The tactic has proved moderately successful in some areas, but the extra fresh water creates lower-than-normal salinity levels in Barataria Bay and Breton Sound, which flank the southeast portion of Louisiana that juts out into the gulf.

Some biologists are worried. Mass oyster deaths have been reported in those two areas, early evidence suggesting that the fresh water could be shaking up a delicate ecosystem and a struggling seafood industry — both already threatened by the largest offshore oil spill in U.S. history.

Though the extra flow of fresh water is a temporary measure, biologists are inundated with questions regarding the long-term effect on the area’s once-productive oyster beds and the complex web of animals, such as clams, acorn barnacles and tube worms.

“You’re removing part of the food chain,” said Ed Cake, an oyster biologist based in Mississippi.

Biologists also worry the dropping salinity levels could displace shrimp, speckled trout and southern flounder. The young of all three species live and grow in the tepid, nursery-like conditions of the bayous and inlets of Barataria Bay and Breton Sound.

But the principal concern is the oyster, one of the building blocks of marine life and a key indicator of environmental conditions.

“Oysters become that initial sentinel,” said Earl Melancon, a biological sciences professor at Nicholls State University, about 60 miles southwest of New Orleans. “You don’t know their impact until you look at their annual life cycle.”

On a recent morning, Melancon set out on a forensic mission in Barataria Bay. He was looking for dead oysters and wondering whether next year would see a crop. He knew dead mollusks had been found northeast of here, around Breton Sound.

“I’m fairly confident that what we’re seeing out there is a freshwater event that’s killing everything,” he said before the trip.

Much like a fisherman harvesting a catch, graduate student Dan O’Malley, his blue T-shirt sleeves rolled up to his shoulders, plunged a dredge into the 90-degree brownish green waters of the bay.

He pulled up a muddy heap of hard shells and plopped it onto a silver metal sheet.

“All right,” Melancon said, standing at the helm of the boat. “We got enough there for a sample.”

Oyster shells were wide open, the inner white mother of pearl layer exposed — a sign the oysters hadn’t been dead for long. Hooked mussels, which can tolerate lower salinity levels, were still alive and attached to some of the dead oysters. There was no oil in sight.

“To me, that’s an indication of freshwater mortality,” Melancon said. For the Louisiana native, the scene was heartbreaking. His family migrated here from Nova Scotia 240 years ago.

“Oysters and other animals can’t take this degree of heat and this salinity,” Melancon said.

Each sample yielded the same results.

“Are you finding anything alive?” Melancon asked Justin Sancho, another graduate student, at the next stop.

“No.”

When the water is warm, as the gulf is this time of year, oysters require a salinity of 5 to 15 parts per thousand. Any less and there’s not enough salt in the water for the larvae or adults to survive, or for spats (young oysters) to firmly attach to the beds below. The mollusks can handle fluctuating salinity levels, but only for so long.

Louisiana Gov. Bobby Jindal and the U.S. Army Corps of Engineers began flushing fresh water through Barataria Bay and Breton Sound on April 30, 10 days after the Deepwater Horizon oil rig explosion.

“The idea is that the oil is being moved about by current and wind, and anything that can affect that flow is a good thing,” said John Lopez, a coastal scientist and director of coastal sustainability for the Lake Pontchartrain Basin Foundation. “It worked. But it didn’t work perfectly, because otherwise we wouldn’t have had oil come onto shore.”

The water diversion was also seen as a solution that was relatively low-cost — nothing had to be built — and that didn’t require money from the federal government or BP, he said.

Oyster farmers began finding dead oysters in June. State officials are taking water and animal samples from a variety of bayous. Recent trips were made by staff from the Louisiana Department of Wildlife and Fisheries. Biologists such as Cake — hired by lawyers and seafood farmers — have also spent the last few weeks out on the water, taking samples.

The results, so far, have been bleak. “The bigger picture is that a whole community of animals that are allied with and related to and live amongst the oysters will be gone,” Cake said.

But there’s hope. As the scientists move a few miles away from the freshwater flow — and closer to the oil-tainted waters of the gulf — they brighten a bit.

About 10 miles north of the Louisiana town of Grand Isle, where oil rigs dot the horizon and white poles marking fishermen’s leases jut out of the sea, O’Malley plunged his dredge in the water again. Limp booms, set out to collect oil just in case some appeared, floated in the distance.

A student announced the salinity: 7 parts per thousand — just within the range oysters need to survive.

For the first time that day, they found some oysters with tightly closed shells. “I’m seeing some live oysters here,” Melancon said.

A student grabbed a hatchet and pried one open. Sancho, mud on his forehead, eyed the large lump of gray oyster meat.

“That’s a pretty one right there,” he said. “I’m tempted to scrape that one out and eat it.”

The students, wearing gloves, wrapped the oysters in aluminum foil and tucked them in plastic bags for analysis later.

nicole.santacruz@latimes.com

p.j.huffstutter@latimes.com