Oil Spill to Slowly Poison Alabama Marsh?

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Salt Marsh

Photograph by Chris Combs, National Geographic

Oil from the Gulf of Mexico spill is making a "real mess" out of sensitive salt marshes, such as this state-owned reserve pictured July 3, 2010, near Grand Bay, Alabama, one scientist says.

That's because the oil may slowly poison marshes that are critical nurseries for the majority of the Gulf's marine life, including shrimp and commercial fish, according to William Finch, a senior fellow with the Washington, D.C.-based nonprofit the Ocean Foundation.

(See related pictures: "Heavy Oil Seeping Into Louisiana Marshes.")

What's more, marsh ecosystems have less resistance to oil, which—once it's carried inland with the tide—tends to stick around longer in the low-lying wetlands, said Finch, a longtime Alabama conservationist.

"You're not going to see sudden death in this marsh—you're going to see things so screwed up that the marsh will die over the next year or two."

—Christine Dell'Amore

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Marsh "Cows"

Photograph by Chris Combs, National Geographic

The "cows" of the wetland, marsh periwinkle snails (pictured near the oily surface July 3) graze marsh plants at a fast rate, Finch said.

In normal circumstances, the plants can handle the onslaught because they also grow fast, and because predators such as crabs keep the snails in check, he said. (Learn about the marine food chain.)

But the oil may both slow the plants' productivity and wipe out a generation of crabs, creating an explosion of snails that eat away the remaining marsh, he explained.

"What we can predict is some serious loss of marsh that will be blamed on the snail," Finch said. "But ... the snail is doing what the snail has always done—it's the fact that the oil has knocked out the two other pieces of the ecosystem: The ability for the marsh to grow fast enough and the major predator of the snails."

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Slash Pine Savanna

Photograph by Chris Combs, National Geographic

The slash pine savanna that abuts Grand Bay marsh (pictured, with a golden canna, on July 3) is now a rarity. Human development and a loss of natural fires—which helped create favorable conditions for savanna plants—have dramatically reduced the ecosystems, Finch said.

Many types of unusual native plants abound in such savannas, such as cannas and giant iris in saltier areas, and insect-devouring carnivorous plants such as butterworts, sundews, and pitcher plants in freshwater areas. (See carnivorous-plant pictures in National Geographic magazine.)

"When you see grasses waving like that, and they're native grasses, something's good," Finch said as he stood in the waist-deep meadow.

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Oil-Producing Plants

Photograph by Chris Combs, National Geographic

Although massive amounts of oil exposure can be detrimental to marsh plants (pictured: a Grand Bay marsh on July 3), the plants also naturally produce oil in small quantities, Finch noted.

"There's almost no component of oil that can't [naturally] be found in this marsh," he said, including oil ingredients phenol and benzene.

Plants probably produce the toxic compounds to discourage predators from gnawing on them too much. And marsh microbes win out because they eat—or break down—the oil that the plants create. (Read how nature is cleaning up the Gulf oil spill.)

"The trouble is," Finch said, that if there's an influx of heavy oil, the oil-eating microbes might go haywire, sucking up all the oxygen and possibly creating an oxygen-deprived zone. (See "Gulf Oil Spill a 'Dead Zone in the Making'?")

It's also much harder to remove the oil from coastal marshes, since some management techniques—such as controlled burns—are more challenging in those environments, Texas Tech University ecotoxicologist Ron Kendall said on May 12.

"Once it gets in there," he said, "we're not getting it out."

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Sailfin Mollies

Photograph by Chris Combs, National Geographic

"Stunning" neon-colored fish (including these male electric-blue sailfin mollies, pictured July 3) court and spawn in the shallow pools of Grand Bay's salt marshes, Finch said.

"Even from here you can see this shine that comes from fish," he said as he watched the courtship "dances" in July. "It's really astonishing" how the males can turn the colors on and off to impress females.

(Related: "Male Fish Punish Unruly Females—And Benefit, Study Says.")

Such pools are "areas that I worry so much about," Finch added, "because they are so heavily utilized" by fish during mating and spawning.

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Fiddler Crab

Photograph by Chris Combs, National Geographic

One of the "most productive marshes you'll run into in the Gulf," the marshes of Grand Bay are home to a "frenzy of life": shorebirds, dancing fish, snails, and crabs, among others, Finch said.

"When the water descends, you'll see literally tens of thousands of crabs that march across these flats—it's unbelievable."

Yet Finch worries about the 2011 crops of several species of crabs (pictured, a fiddler crab on July 3). The feisty little crustaceans have "been really hit hard by this oil out in the Gulf, because all crabs reproduce and grow in the Gulf of Mexico and then come back on shore," he said.

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Marsh Tracks

Photograph by Chris Combs, National Geographic

Though the Gulf oil spill is a disaster for the marshes, these ecosystems have already been disappearing fast due to human activities, Finch said on the Nature Conservancy blog.

"Some marsh is filled outright, some choked with runoff and waste. The rest is squeezed—between the houses competing for a picture window view and the seas that have been rising steadily—about a foot in the last century," he wrote. (Read how coastal areas are being destroyed.)