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Going Green: Habitat in harm's way

Marshes, methane and hypoxia are chief worries in the Gulf

By Lisa Duchene
August 01, 2010

No one knows how 60,000 barrels of oil gushing daily into the Gulf of Mexico will affect future supplies of Gulf white and brown shrimp, blue crab, red snapper, oysters, redfish, mullet and dozens of other species.

Venice, La., shrimper Berlin Moreau had a bleak outlook on June 28, or Day 70 of the disaster. Unable to fish, Moreau was working for British Petroleum, towing a red boom from 
his trawler.

The bottom line, Moreau said from the docks - where the stink of oil had replaced the fresh, salty scent of the sea - was that oil was destroying Gulf seafood, but to what extent was anybody's guess.

"It's in all depths of the water," he said. "No doubt, it will get in the marsh and that's going to hurt wildlife right there. [The marsh] is all the breeding grounds."

Destruction of critical marsh habitat and high levels of methane potentially trapped in deep water that create oxygen-depleted dead zones were the chief concerns of scientists as of early July. Still, they noted reasons for optimism: For instance, the wipeout of any one year-class of a Gulf seafood species is unlikely.

Scientists say the disaster is unprecedented in scope and scale. So much is unknown, including distribution of oil in Gulf fish habitats, effects of oil on reproductive abilities of fish and shellfish and toxicity of the dispersants used. Three key areas that scientists are focusing on are methane, low-oxygen zones and damaged marshland.

 

Methane buildup

A troubling indicator of impacts to the Gulf ecosystem is invisible. The gusher is releasing huge amounts of methane into the water column, according to research conducted by Samantha Joye, an oceanographer at the University of Georgia. Gas represents about 40 percent of the hydrocarbons found in the reservoir tapped by the Deepwater Horizon rig, according to Joye. Methane comprises most of that gas.

Microbial breakdown of methane can rob the water of oxygen and initial research indicates methane may be trapped in deep water. Methane concentrations were very high at depths greater than 3,000 feet in an area ranging 
from 1,600 feet from the blowout to eight miles away. This was found during research conducted in mid-June by David Valentine from the University of California at Santa Barbara and John Kessler from Texas A&M University.

 

Low-oxygen zones

Scientists are predicting this year's Dead Zone in the Gulf - an area of oxygen-depletion caused by decaying algal blooms triggered by excess nutrients - to measure 6,500 to 7,800 square 
miles, about the size of New Jersey. The BP oil gusher could increase the zone, decrease it or have no effect, say scientists.

Researchers from Dauphin Island Sea Lab in Alabama have found a low-oxygen zone off the coast that has persisted for more than a month. For a 40-mile stretch around Dauphin Island, researchers from the Sea Lab measured low oxygen levels from 40 miles offshore to within one or two miles of the shoreline. Fish that could swim away appear to be pushed up against the shore, leaving dead plankton and sea stars behind in the zone.

"There is growing concern within the scientific community that use of dispersants at depth may have trapped the toxic substances within the Gulf of Mexico where they threaten the 
existing populations and could pose a long-term issue for the food web upon which we sit at the top," according to a press release from the 
Sea Lab.

"It's not little local pockets," says Monty Graham, senior marine scientist at the Marine Lab and assistant professor at the University of South Alabama, who is tracking the zone.

"It's over a regional scale. It wouldn't surprise me if there were a band of low oxygen over that entire area between the Mississippi River and Apalachicola, Fla.," adds Graham.

 

Marshes disappearing

Louisiana's wetlands and bayous, which are rich wildlife habitats , are already 
disappearing at the rate of 25 to 35 square miles per year since the levees and canals aimed at preventing flooding 
of the Mississippi no longer deliver needed nutrients and sediments to the marshes. Myron Fischer, a marine scientist and director of the Louisiana Department of Wildlife and Fisheries Research Laboratory at Grand Isle, La., said on Day 72 in late June that the oil had come 13 to 15 miles up 
into the northern reaches of Barataria Bay.

"It's in the grass. It's in the mangroves. Biologists are making daily runs. They're reporting that the mangroves are dead and dying. The grass is bent and dying," says Fischer.

Grasses hold wetlands in place. Losing them means losing the marsh to open water, and wetlands hold 10 to 15 times the number of animals as open water.

"My gut feel right now," says Dr. Larry McKinney, executive director of the Harte Research Institute for Gulf of Mexico Studies in Corpus Christi, Texas, "is that we will see a significant increase in productivity as [wetlands loss] happens (for a year or two) - basically, the wetlands are eating itself as large areas convert to open water and release stored nutrients. This will be followed by a sharp and long-term decline to some lower productivity level."

But Edward Chesney, an oceanographer who specializes in fisheries with Louisiana Universities Marine Consortium, argues the opposite view.

"We've been losing marsh for a long period of time," says Chesney, and the Gulf has still sustained a high level of fish and shellfish production.

Chesney remains optimistic. "One of the things that's good about the system we have down here," he says, "is that some of our most productive species that are important economically and ecologically are short-lived. They should be able to recover very quickly if the habitats they need to sustain their 
production aren't damaged too badly."

So far, a hopeful sign is that effects, while large, are not expected to be Gulf-wide. The damage so far is not "system-wide," said Steve Murawski, director of scientific programs and chief science advisor for the National Marine Fisheries Service. Fish metabolize and clear oil quickly, he adds. NMFS vessels have been sampling swordfish, yellowfin tuna and bluefin tuna eggs and larvae for oil contamination. Bluefin tuna spawn April to June in an area south of the well in 
an arc over to the Florida coast.

Chesney does not think a whole year class of any Gulf 
seafood will be lost, but that recruitment and abundance is likely to decline.

"I don't know," says Chesney. "There's nobody on the planet who knows, because we don't know the extent of the damage so far and we don't know how this is all going to turn out."

 

 

Contributing Editor Lisa Duchene lives in Bellefonte, Pa.

 


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