The Cahaba: A River of Riches- page 2 | Science | Smithsonian
The 190-mile-long Cahaba River is home to many rare species, some of which were thought to be extinct. The showy Cahaba lily (at Halfmile Shoals) thrives in clean, clear, rapidly flowing water. (Beth Maynor Young)

The Cahaba: A River of Riches

An unsung Alabama waterway is one of the most biologically diverse places in the nation, home to rare flora and fauna

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(Continued from page 1)

One May evening, Haddock paddled out to a shoal and settled in among the lilies. He waited through one night and into the next, until finally he saw something flitting from flower to flower. Luckily, the pollinator then flew close enough to Haddock for him to identify it as a sphinx moth—solving one of the Cahaba River's many long-standing mysteries.

Haddock is still plumbing the Cahaba's secrets. He pauses near an especially dense stand of lilies, clambers out of his canoe and picks his way over the rocks until he finds a Cahaba pebblesnail, no larger than a ball bearing.

Until a few years ago, this snail was thought to be extinct, just one more species lost to the wave of extinctions on Southeastern rivers. Plant and animal species took refuge in the region during the last ice age, when glaciers covered the north, then thrived and diversified for millennia in the region's wet, warm climate. But as rivers were dammed for hydropower and transportation over the past century, species began to blink out.

The region's lush rivers—which the eminent biologist and Alabama native E. O. Wilson calls an "aquatic treasure house"—continue to lose species. Alabama now leads the lower 48 in extinctions, due mostly to disappearances among its freshwater fauna: the Coosa River, which runs alongside the Cahaba a few dozen miles to the east, lost 34 species of snails—half its entire inventory—in the 50 years between 1914 and 1964. This is considered by many experts to be the largest recent extinction event of any kind in the United States.

The Cahaba, too, has suffered casualties. Because of water pollution and other stresses such as sediment from erosion, almost a quarter of its original complement of mussel species has disappeared, and snails and fish are thought to have experienced similar declines. But the Cahaba, only 190 miles long, has also held on to a remarkable number of its native plants and animals—including 13 species of snails found nowhere else in the world, among them the humble Cahaba pebblesnail. In 2004, a visiting Australian biologist discovered that the snail thought to be extinct was simply hiding on the underside of rocks, where no one had bothered to look.

Several years ago, a Georgia botanist named Jim Allison identified eight previously unknown flower species along the river, an almost unheard-of haul in contemporary North America. The plants grow on a rare type of magnesium-rich rocky soil. Further investigation turned up eight more species never before found in the state, including one not seen anywhere since the 1830s. The Cahaba River's allies feel certain that more biological treasures lie in the glades, oxbows and shoals—all just waiting for someone to study them.

Such discoveries—and rediscoveries—are worth celebrating, say Haddock and other biologists. Snails and mollusks may not inspire us like bald eagles or blue whales or, for that matter, the flashy Cahaba lily. But they form the bedrock of healthy ecosystems, maintaining water quality by eating algae, feeding ducks, fish, crayfish and turtles, and, through their sensitivity to pollution, serving as early indicators of environmental trouble. "For these river systems in the Southeast, they are the keystone species," says Paul Johnson, program supervisor of the Alabama Aquatic Biodiversity Center.

When local game warden Ricky LeCroix buzzes up to the shoal in his airboat to say hello, Haddock is holding a tiny endangered snail called a cylindrical lioplax—and is engaged in an earnest lecture on snail sex. Some snails are both male and female, Haddock explains. But since the lioplax has separate sexes, it must work harder to find a mate in order to reproduce.

"Yeah," drawls LeCroix. "And when you only move six inches a year, you sure can't play hard to get."

But the Cahaba is more than a museum of rare Southeastern river species. It also serves as a laboratory for their recovery, thanks to the recent demolition of the Marvel Slab, a road crossing built in the 1960s as a shortcut across the river for coal trucks. Though a row of small culverts allowed water to flow through the structure, it acted like a dam and changed the speed of the current, destroying snail and mussel habitats and blocking fish as they tried to swim upstream to spawning grounds.

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